1
MICHAEL OKONKWO C.
PG/M. Sc/09/51723
THE EFFECT OF 4-ACYL SUBSTITUENTS ON THE INFRARED STRETCHING
FREQUENCIES OF SOME 1-PHENYL -3- METHYL -4- ACYLPYRAZOL -5-ONES
AND THEIR MAGNESIUM (II) ,COBALT(II), COPPER (II) AND ZINC (II)
CHELATES.
PURE AND INDUSTRIAL CHEMISTRY
A THESIS SUBMITTED TO THE DEPARTMENT OF PURE AND INDUSTRIAL
CHEMISTRY, FACULTY OF SOCIAL SCIENCES, UNIVERSITY OF NIGERIA, NSUKKA
Webmaster
Digitally Signed by Webmaster’s Name
DN : CN = Webmaster’s name O= University of Nigeria, Nsukka
OU = Innovation Centre
MARCH, 2011
2
THE EFFECT OF 4-ACYL SUBSTITUENTS ON THE INFRARED STRETCHING FREQUENCIES OF SOME 1-
PHENYL -3- METHYL -4- ACYLPYRAZOL -5-ONES AND THEIR MAGNESIUM (II) ,COBALT(II), COPPER (II) AND
ZINC (II) CHELATES.
BY
OKPAREKE OBINNA CHIBUEZE
PG/MSC/06/42054
DEPARTMENT OF PURE AND INDUSUTRIAL CHEMISTRY
UNIVERSITY OF NIGERIA, NSUKKA
MARCH 2011
3
TITLE PAGE
THE EFFECT OF 4-ACYL SUBSTITUENTS ON THE
INFRARED STRETCHING FREQUENCIES OF SOME 1-
PHENYL -3- METHYL -4- ACYLPYRAZOL -5-ONES AND
THEIR MAGNESIUM (II) ,COBALT(II), COPPER (II) AND
ZINC (II) CHELATES.
BY
OKPAREKE OBINNA CHIBUEZE
PG/MSC/06/42054
BEING A RESEARCH PROJECT SUBMITTED TO THE DEPARTMENT OF
PURE AND INDUSUTRIAL CHEMISTRY, UNIVERSITY OF NIGERIA,
NSUKKA IN PARTIAL FUFILLMENT FOR THE AWARD OF MASTER OF
SCIENCE DEGREE IN PHYSICAL CHEMISTRY
4
CERTIFICATION
I hereby certify that Okpareke Obinna Chibueze , a postgraduate
student in the department of pure and industrial chemistry with
registration number PG/MSc/06/42054 has satisfactorily
completed the requirements for course and research work for the
award of a degree of masters in physical chemistry, The work
embodied in the research work is original and has not been
submitted in part or full for the award of any other diploma or
degree in this or any other university.
Prof. E. C Okafor Dr P.O Ukoha
Supervisor Head of Department.
5
ACKNOLEDGEMENT
Iam immensely grateful to my supervisor Prof E.C Okafor for his fatherly guidance and
assistance during the course of this work. I also wish to express my profound gratitude to
Dr C.O.B Okoye and the department of Pure and Industrial chemistry for giving me
graduate assistanship at a time this research work was almost coming to a halt. My
appreciation and gratitude also goes to Mr J.N Asegbeloyin for his immeasurable
assistance during the course of this work,Dr P.O Ukoha for always listening and
providing advice whenever I came calling with my research problems, Mr F.O Ukoha of
S.E.D.I Enugu ,J.I Ugwu; E.I Mborji,and S.I Odoh for their technical assistance.
I also express my gratitude to my colleagues and friends ,Mrs Ijeoma, Chizoba,Toluhi,
Mrs Ibekwe ,Felix ,Solo Okereke,Atiga, Helen, Mr Ujah,Mr Ayuk, Iyke Odoh and
Chijioke olelewe for their encouragement and support. My gratitude also to my uncle
Architect Chidi Onwuka for his financial and moral support during this work and Mr T,O
Ujam of the University of Waikato Newzealand for his assistance in carrying out the
analysis, To my parents Mr and Mrs S.N Okpareke and my siblings for their support and
understanding and finally to God Almighty for his infinite mercy.
6
DEDICATION
To a very special friend, Evelyn Fuludu for urging me on.
7
ABSTRACT
The divalent metal chelates of Mg,Co,Cu and Zn with 4-acetyl (hpmap), 4-
benzoyl(hpmbp),4-butyryl(hpmbup),4-capyroyl(hpmcp),4-propiony
(hpmprp) and 4-palmitoyl(hpmpp) derivatives of 1-phenyl -3-methyl
pyrazol-5-one have been synthesized and characterized by UV ,IR, and
conductivity measurements. It is shown that the ligands behaved like
bidentate enols, all forming neutral chelates with the metal ions , bonding
through oxygen of the enolic hydroxyl group and /or the oxygen atom of
the carbonyl group of the ligands keto-enol tautomer. The i.r spectra of the
ligands and their chelates have been measured between 4000cm-1
and
400cm-1
and assignments proposed for observed frequencies. The effect of 4-
acyl substituents on the carbonyl stretching frequencies of the complexes
was also investigated and the results showed that there was an increase in the
carbonyl stretching frequency bands as the length of the alkyl substituent
increased for magnesium (II),cobalt(II) and copper (II) chelates and the
reverse trend was observed for zinc (II) chelates.The infrared carbonyl and
metal oxygen stretching frequencies of the transition metal chelates were
also compared with the Irving and Williams stability order for transition
metal complexes(Cu > Ni >Co >Mn >Zn) and it was observed that the
magnitude of the M-O stretching frequencies followed closely the Irving
Williams stability order while the C=O stretching frequencies did not. This
+has been attributed to electronic and steric effects.
8
TABLE OF CONTENTS
Title page …………………………………………………………………………….. ii
Certification …………………………………………………………………….. iii
Acknowledgement ……………………………………………………………….. iv
Dedication …………………………………………………………………. v
Abstract ……………………………………………………………………… vi
List of figures ……………………………………………………………… xi
List of tables ……………………………………………………………………. xiii
Abbreviations ………………………………………………………………… xiv
CHAPTER ONE
1.0 Introduction ……………………………………………………… 1
CHAPTER TWO
2.0 Literature review ……………………………………………………………… 4
2.10 Concept of Chelation ………………………………………………………….. 4
2.11 Metal chelate complexes …………………………………………………………. 5
2.12 Ion –pair complexes …………………………………………………………….. 5
2.13 Additive complexes ……………………………………………………………….. 5
9
2.20 Chelation with β-diketones ……………………………………………………… 6
2.30 Chelation with 4-acylpyrazolones ………………………………………………… 8
2.40 Stability of metal chelates ………………………………………………….... 10
2.41 Nature of the chelating agent …………………………………………………..10
2.42 The size of the chelate ring ……………………………………………… 11
2.43 The nature of the central metal …………………………………………….. 11
2.44 The nature of the metal-ligand bond ……………………………………….. 11
2.50 Previous work done with β-diketones …………………………………… 12
2.51 Physical properties and structure elucidation ……………………………… 13
2.52 Isolation and spectroscopic studies …………………………………………. 15
2.60 Previous work on metal chelates of β-diketones ………………………………..17
2.61 The chemistry of magnesium …………………………………………………...17
2.62 Review of previous work done on magnesium chelates of β-diketones ………..19
2.70 Chemistry of cobalt ………………………………………………………19
2.71 Review of previous work done on cobalt chelates of β-diketones …………….23
2.80 The chemistry of copper ………………………………………………………..24
2.81 Previous work done on copper chelates of β-diketones …………………………26
2.90 The chemistry of zinc …………………………………………………………… 28
2.91 Previous work done on zinc chelates of β-diketones ……………………………...29
10
2.92 Spectroscopic techniques used in the study of ligands and metal complexes …… 30
2.93 Ultraviolet spectroscopy ……………………………………………………… 30
2.94 Infrared spectroscopy ………………………………………………………… 31
CHAPTER THREE
3.0 Experimental …………………………………………………………. 33
3.1 Laboratory apparatus and equipments ……………………………………….. 33
3.2 Laboratory reagents ……………………………………………………………. 33
3.3 Synthesis of 1-phenyl-3-methyl-4-acylpyrazol-5-ones …………………………35
3.31 Synthesis of 1-phenyl-3-methyl-4-acetylpyrazol-5-ones (HPMAP) …………… 35
3.32 Synthesis of 1-phenyl-3-methyl-4-benzoylpyrazol-5-ones (HPMBP) …………… 35
3.33 Synthesis of 1-phenyl-3-methyl-4-propionylpyrazol-5-ones (HPMPRP) ……… 36
3.34 Synthesis of 1-phenyl-3-methyl-4-butyrylpyrazol-5-ones (HPMBUP) ………… 36
3.35 Synthesis of 1-phenyl-3-methyl-4-hexanoylpyrazol-5-ones (HPMCP) …………. 36
3.36 Synthesis of 1-phenyl-3-methyl-4-palmitoylpyrazol-5-ones (HPMPP) ………… 36
3.40 Synthesis of 1-phenyl-3-methyl-4-acyllpyrazolonates …………………… 36
3.41 Synthesis of 1-phenyl-3-methyl-4-acetyl-5-pyrazolonato magnesium II complex 36
3.42 Synthesis of 1-phenyl-3-methyl-4-acetyl-5-pyrazolonato copper II complex ……37
3.43 Synthesis of 1-phenyl-3-methyl-4-acetyl-5-pyrazolonato cobalt II complex …… 38
3.44 Synthesis of 1-phenyl-3-methyl-4-acetyl-5-pyrazolonato zinc II complex …… 39
11
3.45 Preparation of 3M hydrochloric acid solution ……………………………………39
3.50 Physical and spectroscopic analysis …………………………………………… 42
3.51 Melting point determination …………………………………………….. 42
3.52 Conductivity measurement ………………………………………....... 42
3.53 Electronic spectra measurement ……………………………………………... 42
3.54 Infrared spectra measurement …………………………………………… 42
CHAPTER FOUR
4.0 Results and Discussion …………………………………………………. 43
4.10 Structure of ligands and complexes ……………………………………… 43
4.20 Physical data ………………………………………………………………….. 45
4.30 Conductivity Measurement ………………………………………………… 48
4.40 Solubility survey of ligands and complexes ………………………………… 49
4.50 Electronic spectra of ligands and complexes ………………………………….. 51
4.60 Infrared spectra of ligands and complexes …………………………………… 53
4.70 The effect of 4-acyl substituents on the infrared carbonyl stretching frequency of
metal(II) chelates of some 1-phenyl-3-methyl 4-acylpyrazolone ……………………...64
4.80 Conclusion ……………………………………………………………… 69
References ……………………………………………………………….. 71
Appendices .......................................................................................... 86
12
LIST OF FIGURES
Figure 1: Tautomeric forms of a typical β-diketone…………………………………… 6
Figure 2: Zinc (II) acetylacetonate ……………………………………………………. 7
Figure 3: Copper (II)ethylenediammine ……………………………………………… 7
Figure 4: 1-phenyl-3-methyl-4-acylpyrazolone ………………………………………. 8
Figure 5: Tautomeric forms of the 4-acylpyrazolone ……………………………………9
Figure 6: Intramolecular hydrogen bonding in the forms of the ligand ………………….9
Figure 7: Copper (II) chelate of 4-trifloroacetyl pyrazolone ……………………… 10
Figure 8: Tautomeric forms trifloroacetyl pyrazol-5-one ………………………… . 14
Figure 9: Reaction scheme for the synthesis of 1-phenyl-3-methyl-4-acylpyrazolones and
their metal complex. …………………………………………………………… 41
Figure 10: Tautomeric forms of the ligand ………………………………………….. 43
Figure 11: Structure of the metal complex ………………………………………….. 44
Figure 12: Plot of infrared carbonyl stretching frequency against molecular weight of
ligands ………………………………………………………………………………… 65
Figure 13: Plot of infrared carbonyl stretching frequency against molecular weight for Mg
(II) chelates …………………………………………………………………………….. 66
Figure 14: Plot of infrared carbonyl stretching frequency against molecular weight for Co
(II) chelates ………………………………………………………………………….... 66
Figure 15: Plot of infrared carbonyl stretching frequency against molecular weight for Cu
(II) chelates …………………………………………………………………………… 66
13
Figure 16: Plot of infrared carbonyl stretching frequency against molecular weight for Zn
(II) chelates ……………………………………………………………………………. 67
Figure 17: Plot of infrared metal-oxygen stretching frequency against molecular weight
for Mg (II) chelates ………………………………………………………………… 67
Figure 18: Plot of infrared metal-oxygen stretching frequency against molecular weight
for Co (II) chelates ……………………………………………………………………..68
Figure 19: Plot of infrared metal-oxygen stretching frequency against molecular weight
for Cu (II) chelates ……………………………………………………………………. 68
Figure 20: Plot of infrared metal-oxygen stretching frequency against molecular weight
for Zn (II) chelates …………………………………………………………………… 69
14
LIST OF TABLES
Table 1: Physical data for some 4-acylpyrazolones ……………………………………45
Table 2: Some physical data for Mg (II), Co (II),Cu (II) and Zn (II) complexes of some 1-
phenyl -3-methyl-4-acylpyrazolon-5 ………………………………………………….46
Table 3: Conductivity data. …………………………………………………………… 48
Table 4: Solubility data for the ligands and metal complexes. ……………………… 49
Table 5: Electronic spectral data for the ligands and their metal complexes ………… 52
Table 6: Infrared spectral data for the ligands and their metal complexes …………….. 53
Table 7: Infrared carbonyl and metal-oxygen stretching frequencies of the ligands and
their metal complexes …………………………………………………………………. 63
15
ABBREVIATIONS
HPMP: 1-Phenyl -3-methyl -4-acyl pyrazol-5-one
HPMAP: 1-Phenyl-3-methyl-4-acetyl pyrazol-5-one
HPMBP: 1-Phenyl-3-methyl-4-benzoyl pyrazol-5-one
HPMBUP: 1-Phenyl-3-methyl-4-butyryl pyrazol-5-one
HPMCP: 1-Phenyl-3-methyl-4-capyroyl pyrazol-5-one
HPMPRP: 1-Phenyl-3-methyl-4-propionyl pyrazol-5-one
HPMPP: 1-Phenyl-3-methyl-4-palmitoyl pyrazol-5-one
HTTA: Thenoyltrifluoroacetylacetone
DMSO: Dimethylsulphoxide
DMF: Dimethylformamide
TBP: Tris-n-butylphosphate
TOPO: Triocitylphosphineoxide
MIBK: Methylisobutylketone
EDTA: Ethylenediamminetetraacetate
THF: Tetrahydrofuran
16
CHAPTER ONE
1.0 INTRODUCTION
There has been a lot of interest in the chemistry and stereochemistry of metal
complexes in recent years because of its growing applications in both biological and chemical
processes. The chemistry of these groups of compounds was first proposed in 18931
by a
Swiss chemist, Alfred Werner who used his coordination theory of primary and secondary
valences to account for the phenomenon by which apparently all stable saturated molecules
combine to form molecular complexes.2,3
Werner showed that the properties of many
complexes formed by various transition metals could be explained by the postulate that the
metal atoms have a ligancy of six or four, with the attached groups arranged about the central
atom at the corners of a circumscribed regular octahedron or tetrahedron.4 Almost every
kind of metal atom can serve as a central atom in a complex , although some metals like the
transition metals do so more readily than others.5 When a metal atom coordinates with two or
more donor groups of a single ligand called the chelating agent , a chelate is formed. One of
the significant features of these chelating agents is that whereas complex formation may
involve more than one intermediate step, Chelation is a one step process. 6,7
Since Urbain,s work on the structure and reactivity of β-diketones in 1896,
8 these
groups of chelating agents have been of utmost importance to chemist and research workers
alike. These β-diketones are ligands bearing two carbonyl groups separated by a methylene
group. The intervening methylene group bears an active hydrogen atom.9.
The acidity of the
hydrogen atom is caused by the electron withdrawing powers of the two carbonyl groups that
flank them. Owning to electronic and field effects , the hydrogen atoms are capable of
migrating to any of the carbonyl groups giving rise to tautomers.10
1-phenyl -3-methyl -4-acyl pyrazolone , a typical β-diketone whose synthesis was first
described by Jensen, 11,12
has gained considerable popularity in recent years.13-15
The
17
structural features of these keto-enol tautomerides attracted the attention of research workers
like Okafor 16-19
and Uzokwu 20-22
who synthesized and characterized a good number of their
metal Chelates. Research into these group of β-diketones has been stimulated by their
potential application in the extraction of metal ions from acid solutions. 23-24
Some other
workers have used the 4-chloroacetyl and 4-triflouroacetyl derivatives of this ligand for the
spectrophotometric determination and extraction of trace elements from aqueous solution.
Mirza and others synthesized the benzoyl derivative of 1-phenyl-3-methyl-4-acyl- Pyrazolone
and used it in the extraction and separation of thorium from titanium, uranium and the rare
earths,27
while Hassany and Quereshi reported the extraction of group IB, IIB and III- IVA
elements using the 4-trichloroacetyl derivative of the pyrazolone moeity. Okafor 16,19,28
has
equally used the triflouro derivative in the isolation of a good number of metal chelates.
Apart from the application of these groups of compounds in qualitative and
quantitative analysis , 4-acyl pyrazolones have found application in medicine, as strong active
ingredients in analgesic 29-30
and in chromatography for the construction of mixed ligand
resins for trapping toxic metals.30
The antipyrene and some other derivatives have been found
to exhibit some biological and pharmacological properties.25,29,31
They have equally found
use in antihistamines, antipyretines, antirhematics and antiinflamatory drugs.32-33
Some
derivatives of this compound containing azo groups have also been used as antifungal and
antiparasitic agents. Recently, several pyridoxine and pyrollo- pyrazole derivatives of the
pyrazole moiety have been synthesized and reported to be useful as inhibitors of
phosphodiestrate(iv) and tumour narcosis factor.35-38
They have also been applied in the
treatment of asthma, arthritis and septic shock.35
The acyl hydrazine compounds of
pyrazolone have been found to serve as inhibitors for many enzymes and an excellent
component of many chemotherapeutic drugs for the treatment of cancer.39
Some other
derivatives have been used as corrosion inhibitors for steel in hydrochloric acid solution.40
To date, a lot of research work has appeared in literature on the structure, reactivity and
18
spectral properties of 4-acyl pyrazolones and their derivatives11-40
. This project investigates
the effect of the 4-acyl substituents on the carbonyl and metal-oxygen stretching frequencies
of some 4-acyl pyrazolones and their Mg(II) ,Co(II), Cu(II) and Zn(II) chelates.
19
CHAPTER TWO
2.0: LITERATURE REVIEW
2.10 Concept of Chelation
Chelate complexes of many metal atoms are known 41-43
and with a given chelating agent, the
properties of the complexes change from one metal atom to another. There is a great
uncertainty, that a chelating agent will react with or extract a particular metal specifically in
the presence of other metals, although chelating agents exhibit varying level of selectivity,
depending on the reacting conditions. Chelation is the formation of a ring containing a metal
atom by a multidentate ligand.44
This is said to occur when a ligand with more than one pair
of unshared electrons per molecule donates them to a metal atom,45,46
and the metal to which
electrons are donated must have available orbitals for bond formation with the chelating
agents. These unpaired electrons may be donated by coordinating groups,47,48
Like OR, OH, -
NH2, =N, or SH of the multidentate ligand. These functional groups must be well positioned
in the molecule, so as to allow a favorable chelate ring formation with the central metal atom.
Chelation is always influenced by stearic factors .49-50
Irving and Co-workers have shown
that substitution of a methyl group in the 2-position of 8-hydroxy quinoline prevented the
formation of a tris complex will Al(III), though complexes were formed with larger ions such
as Cr(II) and Fe(III).
During the formation of metal chelates, three classes of metal complexes species are
possible. They are metal chelate complexes, Ion pair complexes and additive complexes. All
these complexes are neutral compounds and there is a possibility of having two of these
complexes in solution at the same time. The formation of these complexes is governed by
certain ionic forces which are related to both the charge, the radius of the metal ion and the
relative tendencies of various metals to form bonds with electron donors. 51-52
20
2.11 Metal Chelate Complexes
These are chelates synthesized by the treatment of a cationic aquometal complex with
a chelating agent which is normally a weak acid. The reaction scheme involves the transfer of
the chelating agent from the organic phase to the aqueous phase and the subsequent
dissociation into proton and a conjugate base of the weak acid. The next step is the
displacement of the water molecule attached to the metal ion by anionic conjugate base group
in a ratio that gives a neutral metal chelate complex. The overall reaction involves bond
breakage and formation of new metal-ligand bonds. These chelates are hydrophobic and
dissolve preferentially in the organic phase53
. The interaction in this kind of complex was
described as short range, since the ions are adjacent to one another and the solvent shell of
each dissociated ion is broken.54
2.12 Ion-Pair metal complexes
Ion-pair complexes are formed as a result of long range electrostatic force of
attraction, thus it is not always necessary that the two interacting ions are close to each other.
These ion-pair complexes are not chelates. The formation of ion-pair metal complexes are in
two stages, the first stage involves the formation of the cation-metal complex in which the
aquo-ligands are substituted by anions in solution. The second stage is the attraction of this
cationic metal complex by an anionic group such that their charges are neutralized. No
covalent bond is formed between the two oppositely charged species because they are held
together by a strong electrostatic force of attraction.
2.13 Additive Complexes
These are metal chelates or ion-pair complexes with additional organic reagents, with
a lone pair of electrons at least, coordinated to the metal as a ligand solvents like TBP,
MIBK, TOPO,57,58
ethanol, DMSO can form additives complexes. Here the organic solvent is
21
acting as a reagent to displace water molecules attached to the metal complexes to from a
hydrophobic additive complexes. An additive complex involving the chelating agent can also
take place when the metals coordination number and geometry of the ligand is favorable and
the concentration of the reagent is high. 59
Another class of additive complexes are formed
when the pH of the solution is high and the metal undergoes hydrolysis. 60-61
They have a
molecular formular of MLn(OH)x where M= metal, L=anion of the ligand.
2.2 Chelation with β-Diketones
1,3 -diketones are bidentate ligands coordinating through oxygen atoms. They are weak acids
with characteristic keto-enol equilibra as show in (fig 1) below.
R
R C
O
C H R C H R 1C
O
R C
O
C
O
R 11
K eto form
R C C
O
R
O
R 11C
R C
O H
C R C
R C C R 1 C
O
R 11 R C
O
C R 1 C R 11
O H
O H
Enol Form s
O H
Fig:1 Tautomeric forms of a typical β-diketone
The presence of at least one proton on the methylene carbon atom results in keto-enol
tautomerism in these 1.3 diketones. These chelating agents can form a six membered chelate
22
ring with a large number of metals by losing one proton, for example acetyl acetone forms a
six membered chelate ring with zinc atom as shown below.
H3C
HC
H3C
C O
OC CO
O C
Zn
CH3
CH3
CH
Fig 2: Zinc (II) acetylacetonate
Ethylene diammine also complexes with copper (II) ion through the unshared pair of
electrons possessed by the nitrogen atoms in the ligand.
H2C
H2N
NH2
CH2
Cu
H2C
H2N
Cu
CH2
NH2
2+
Fig 3: Copper (II) ethylenediamine
Also included in these important class of chelating agents are HTTA, dibenzoyl methane and
the derivatives of the 4-acyl pyrazol- 5-ones. Some research workers like Lempick, and
Samuelson62
investigated the tetrakis rare earth chelates of the benzoyl trifluroacetone and
showed the possibility of laser activity in the compounds. Hinckley63
on the other hand
demonstrated the possibility of having larger isotopic shifts in solutions containing some
rare earth -diketonates, while Uzoukwu and others elucidated the chemistry and structure
of Uranium (vi) and Fe (iii) chelates of 2-thenoyl triflouroaccetone (HTTA) and concluded
they formed neutral complexes in both aqeous and acidic solutions.64
However most of the
work reported in literature on the β-diketones has been on the extraction and concentration of
metal ions 65-67
.
23
2.3 Chelation with 4-acylpyrazolones
The 4-acyl pyrazolones are members of the 1,3-diketone family. They contain both
Nitrogen and Oxygen atoms and form coordination complexes of the Six membered chelate
ring with metal ions through the oxygen atoms in them. Their chemical properties are
determined by the presence of hydrogen on the methylene carbon atom sandwiched between
the two carbonyl groups of the 1,3-diketone as shown in figure 4 below.
CH3 C O
R
O
N
C6H
5
H
N
Where R= Acetyl, benzoyl ,butyryl, Hexanoyl, palmitoyl etc
Fig 4: 1- phenyl -3-methyl -4-acyl pyrazol-5-one.
The two carbonyl groups are not isolated from one another. Due to the migration of the
methylene proton ,four structural isomers are possible as shown in the figure 5a-d.
24
C H3 C O
R
O
N
C6H
5
N
C H3 C O
R
O
N
C6H
5
N
O
C
RH
N
C6H
5
H
C H3
O
C
R
N
C6H
5
C H3
NH
O H
O
N
(a) (b)
(c)(d)
Keto form s
Enol form s
Fig 5: Tautomeric forms of the 4-acyl pyrazolone ligand.
The Enol form, Fig 5 (c) is more favourable in non-polar solvents than the keto form. Due to
conjugation and intramolcular hydrogen bonding, the enol form is stabilized relative to the
keto form. 18,68,
O
C
R
N
C6H
5
CH3
O
N
H
Fig 6 Intram olecular hydrogen bonding in the enol form s of the ligand
25
On Investigating the 4-triflouroacetyl derivative of this ligand Okafor 19
revealed that the
enolic form was more stable than the keto form and obtained experimental evidence that the
stability of the enol forms of the 4-acylpyrazolones was as a result of electronic and stearic
factors. Thus under appropriate experimental conditions the labile enolic proton of the 4-acyl
pyrazolones can be replaced by a metal ion giving a six membered chelate ring with the metal
atom at the centre, bound to an oxygen atom of the chelating agent and accepts a lone-pair of
electron donated by the oxygen of the other carbonyl group. An example is the copper (II)
complex of 4-triflouroacetyl pyrazolone shown in the figure 7.
O
ON
C6H
5
C
C
N
N
CO
O
Cu
CH3
F3
CCH
3
C6H
5
F3
Fig 7: Copper (II) chelate of 4-trifloroacetyl pyrazolone-5-one
Due to Chelation, the electron system of the 1,3-dicarbonyl group bonded to the metal is
delocalized 69,70
.
2.4 Stability of Metal Chelates
The stability of metal chelates is determined by certain factors which include, the nature
of the chelating agent, the size of the chelate ring, the nature of the central metal and the
nature of the metal ligand bond 71,72
.
2.41 Nature of the Chelating Agent
Calvin and Merit, 73,74,75
Confirmed the influential nature of the chelating agent when
they carried out studies on a series of –diketones. Acetylacetone with the pKa of 9.7 forms
more stable complexes than thenoyltriflouoroacetylacetone with pKa of 6.2. This is because
26
of the more basic nature of acetylacetone. On the other hand ,Sidgwick 76
, in 1941 pointed out
that the affinity of a ligand towards a metal atom depends on the donor atom of the ligand.
Most often, these are oxygen, nitrogen or sulphur. Oxygen and nitrogen are known to have
similar affinities for metallic ions and form stable chelates.
2.42 The Size of the Chelate Ring
Investigations have shown that for a chelate ring with minimum strain to be formed,
the bond angles of the participating atoms should be as close as possible to the normal
covalent bond angles. Application of the Baeyer strain theory shows that the five and six
membered ring compounds will be more favored among chelate compounds. But all other
factors being equal, a five-membered chelate ring will be somewhat more stable than its six
membered chelate ring analog. In general, the stability of metal chelates has been said to
increase in the order of four membered < six member ≤ five membered and chelates having
more than six members are not stable except those metal ions that tend to form linear
complexes such as Silver (I) and Mercury (II)77,78
.
2.43 The Nature of the Central Metal
There is reasonable evidence that with the transition metals, there is a gradual change
in the nature of the chelate bond, from essential ionic to covalent as the atomic mass of the
transition metal increases.79
Also the tendency towards covalent character increases with
increase in oxidation state of a transition metal. When there are two or more transition metals
having the same oxidation state, covalency increases with increase in the number of d
electrons.
2.44 The Nature of the Metal-ligand bond
There has been an attempt to classify metals based on their affinity for oxygen,
nitrogen, sulphur or a combination of these atoms.79
In the metal ligand bond, both electrons
27
utilized in the bonding are donated by an atom of the ligand. The stereochemistry and
coordination number of a metal chelate is closely related to the nature of the metal to ligand
bond. 80, 81
Most chelates with metal ligand bonds known to be covalent are observed to be
quite stable, though stereochemical factors relative to the metal to chelate itself do have
influence on the chelate stability. Substitution in the sensitive position of the chelating agent
gives a different effect. The derivatives of 8-quinolinol substituted in the second position for
example, gives less stable complexes than does 8-quinolinol itself. This has been attributed to
stearic hindrance to chelate formation caused by the substituent group.82, 83
2.5 Previous Work Done with β- Diketones
Before Jensen’s work on the 4-acylpyrazolones, 11,12
-diketones such as Acetyl
acetone and their derivatives have been used as analytical reagents for radiochemical work.
85 Recently Uzoukwu and co-workers used derivatives of ethylenediammine and 2-
thenolytriflouroacetone 64
in the extraction and concentration of different metal ions in
solution. Various studies have indicated 1-phenyl-3-methyl-4-acyl pyrazolones as powerful
analytical reagents 11-16
for a variety of metal ions. In comparism to other types of –
diketones, 4-acylpyrazolones have some advantages such as strong acidity, high chemical
stability, hydrophobicity of their chelates, 88
ability to form chelates with high distribution
ratio even in strong acid solutions, relatively low cost of synthesis and their ability to last for
a very long time. In view of this, a good number of publications11-18
describing various 4-
acyl-pyrazalones have appeared in literature and the properties of these compounds and their
chelates have been extensively studied 13,14,23,28,64,65,82
. A good number of the derivatives of
the 4-acyl-pyrazolones have been synthesized.
28
2.51 Physical Properties and Structure Elucidation
The structure elucidation of 4-acylpyrazol-5-ones presents some difficulty due to the
fact that they are potentially tautomeric heterocycles17
. Four tautomeric forms have been
found to be possible. (Fig 5) However it has been reported that the enol tautomer is more
stable than the keto tautomer in non polar solvents. Okafor 17-19
In 1980 and 1981 reported
that the 4-acylpyrazol-5-ones are practically insoluble in water but exhibit high solubility in
most organic solvents. Akama and others 89-91
in their systematic study of alkyl substituted 4-
acyl derivatives of 3-methyl -1-phenyl-pyrazol-5-ones reported that due to its slightly lower
pKa value (lower than 4.0) the 4-benzoyl derivative proved to be more efficient in the
extraction of metal ions than the 4-propionyl and 4-lauroyl derivatives which had pKa values
of about 4.2. These showed that the acid dissociation constant was insensitive to the nature of
the carbonyl group79
. Uzokwu92
equally reported that the pKa value of the corresponding 4-
triflouroacetyl and 4-trichloroacetyl derivatives are lower than the other derivatives and has
been proved to be even more efficient analytical reagents for the determination of metal ions.
Okafor in 1982 19
investigated and reviewed the triflouroacetyl derivative of the 1-phenyl-
3-methyl-4-acyl pyrazol-5-ones and observed that only the enol form of the ligand was
capable of existing in stable form.
29
N
N
C
O
CH3
Cf3
C6H
5
C O
C N
N
C
O
CH3
Cf3
C6H
5
C
C
C
H
O
(I) (II)
N
N
C
O
CH3
Cf3
C6H
5
C
C N
N
C
CH3
Cf3
C6H
5
C
C
C
H
(III)
O H
O
O H
(IV )
H
Fig 8 :Tautomeric forms of 4-triflouroacetyl pyrazol-5-one
The results of his investigation revealed that only one form of the triflouro acetyl derivative
of the 4-acyl pyrazolone existed even when recrystalized from different solvents. He
concluded that the forms obtained from recrystallization from ethanol and water were the
same as revealed by detailed infrared and proton Nmr studies, only that the former contained
one molecule of water of crystallization. This observation refuted the claims of Hasany and
Quereshi 24
who reported that by Jensen’s method, 12
they obtained two forms of the 4-
triflouro-1 phenyl-3-methylpyrazo-5-one when recrystalized from different solvents, (ethanol
and benzene). The enol form being yellowish and the keto form colorless. He went further to
explain that the probability of the form (I) existing is very slim due to the presence of
electron withdrawing groups (C=O, C-N and CF3 which are withdrawing negative charge
from the carbon atom carrying the negative charge. Finally he suggested the possibility of
(II), (III) and (IV) existing and isolable with structure (IV) most likely to be isolated in stable
30
form, this he attributed to the electron releasing nature of C6H5 which counter balances the
electron withdrawing properties of –CF3 group, thus the hydroxyl proton in the structure (IV)
will be more labile than the hydroxyl proton in the structure (III).
2.52 Isolation and Spectroscopic Studies
Uzoukwu and Duddeck 86
in 1998 studied the spectroscopic properties of the metal
complexes of the 4-adipoyl and 4-sebacoyl bis 1-phenyl-3-methyl pyrazolones and using the
analytical and UV spectral data showed that some of the metals formed hydrated complexes
with the chelating agents. They represented these complexes with the general formular
ML.XH20 where M=metal ion, L is 4-acyl bis (1-phenyl methyl pyrazolones) dianion and
x=0,1,11/2
or 2. Molar conductivity measurements of 104M solutions of the complexes, in
DMF recorded values in the 2-5 Ω1cm
2 mol
1 range indicating that all the complexes are
neutral. The infrared spectral data of the metal complexes showed some broad bands at 3150-
3410 cm-1
, indicative of water molecules of the hydrated complexes 87
. The carbonyl
vibrational frequencies which occurred at 1626cm-1
(H2SP) and 1632cm-1
(H2Adp) shifted to
the lower region in the IR spectra of the metal complexes indicating the involvement of C-O
bond in chelation with the metal ion. They assigned the Unique absorption frequencies
appearing below 500cm-1
in the IR spectrum of the metal (II) chelates to asymmetric
stretching frequency vibration of the metal oxygen bonds 88
.
Apart from the works of Uzokwu and Duddeck 86-88
Okafor93
synthesized the rare
earth chelates of 1-phenyl-3-metltyl 4-Benzoyl pyrazol-5-one and studied their spectral
properties. He observed from the electronic spectra, that contrary to general rule, that there
was no bathochromic shift on chelation to a metal as obeyed by other diketonates. The
ligands and complexes had virtually identical absorption maxima, indicating that the π -
bonding system in each ligand anion was almost intact, only the s-orbital of the oxygen atoms
(one orbital being non-bonding and the other having lost a proton) are substantially involved
31
in bonding with the metal ions. Thus there was little or negligible π -electron interaction
amongst the three chelate rings. He also observed from the IR spectral data of both the
complexes and the ligands that there were similarities and a few marked changes in
absorption bands. The main changes observed in the spectra of the ligands when complexed
included the disappearance of the OH-O absorption band centered at 2600cm-1
and the shift
of the C=O stretching frequency from 1640cm-1
in the ligand to 1608cm-1
(vas C=O). The
absence of absorption peaks between 1800cm-1
and 1608cm-1
in all the trischelates was taken
as an evidence of six oxygen atoms of the -diketonate being bonded directly to the rare
earth ion.The manganese (II) and Zinc (II) Complexes of some 1-phenyl-3-meltyl-4-acyl
pyrazolones have been studied and the UV spectral data of both the Mn(ii) and Zn(II)
complexes in chloroform showed absorption bands near 252nm and 286nm, ascribed to π- π*
Intra ligand transition. The IR spectral properties were also studied and it was stated that the
bathochromic shifts in the vas C=O of the metal complexes which occurred at 10-20Cm-1
from the ligand was an evidence that the C=O group of the free ligand was involved in the
Chelation process. It was also observed that the stability of both the CO-M and C=O bonding
systems did not follow any particular trend with respect to the nature of the 4-acyl
substituent. However the absorption bands observed for the 4-trichloroacetyl pyrazolone
complexes of both metals were relatively higher, vas C-O (Mn 1620cm-1
, Zn 618cm-1
) and
vas C O-M (Mn 470cm-1
, and Zn 488cm-1
) than those for the alkyl substituted 4-acyl
derivatives and this was attributed to differences in the nature of the electronic and stearic
interactions between these different groups [94]
.
The complexes of the acetyl, propionyl Butyryl triflouroacetyl and capyroyl with
lanthanides,uranyl, monovalent and divalent metals have been synthesized by Okafor and
others 16,18,19,25,41
and spectroscopic studies carried out on them. They reported a general
formula LaA3 XH2O.YC2H5OH for lanthanide chelates of the 4-acylpyrazolones , where La
is the lanthanide, A is the 4-acyl-pyrazolone anion, X=2 and Y=0 or ½ ,while the other group
32
of metals gave complexes of composition MAn. XH2O where n is charge of the metal M and
X=O, 1, or 2. The results of their investigation also showed that the magnitude of the M-O
stretching frequencies for the transition metals followed very closely the Irving-Williams
stability order 18,79,96
Cu>Ni>Zn>Co>Mn. Some other workers, 23, 24,25
have synthesized other
derivatives of the pyrazole moiety and confirmed that their formula corresponds to the one
reported by Okafor above.
2.60 Previous Works Done on Metal Chelates of β-diketones
2.61 The Chemistry of Magnesium
Compounds of magnesium have been known from ancient times, though nothing was known
of their chemical nature until the seventeenth century 97
. Magnesium like its heavier
congeners Ca, Sr and Ba, occurs in crystal rocks mainly as the insoluble carbonates, sulphates
and silicates. Estimates of its total abundance depend sensitively on the geochemical model
used. Large land masses such as Dolomites in Italy consist predominantly of the magnesium
limestone mineral dolomite [MgCa(CO3)2] and there are substantial deposits of magnesite
(MgCO3) epsomite (MgSO4.7H2O) and other evaporites such as carnalite (K2MgCl4.6H2O)
and langbeinite [(K2Mg2(SO4)3].98
Silicates are represented by the common basaltic mineral
olivine [(Mg,Fe)2SiO4] and by soapstone (talc) Mg3Si4O10(OH)2] and Micas. Magnesium is
produced on a large scale either by electrolysis or by silicothermal reduction. The
electrolytic process uses ester fused anhydrous MgCl2 at 7500C or partly hydrated MgCl2
from sea water at a slightly lower temperature. The silicothermal process uses calcined
dolomite and ferrosilicon alloy under reduced pressure at 11500C.
2(MgO.CaO) + FeSi 2Mg + Ca2SiO4 + Fe
Magnesium like other group 2 metals are not noted for their ability to form complexes. The
factors favoring complex formation are small highly charged ions with suitable empty
33
orbitals of low energy which can be used for bonding.2 Mg usually forms complexes in
solution with oxygen-donor ligands ,(EDTA). It also forms a few halide complexes such as
[Net4]2 [MgCl4] and a very important complex called chlorophyll where magnesium is at the
centre of a flat heterocyclic organic porphyrin ring system , in which four nitrogen atoms are
bonded to the magnesium .(99)
Chlorophyll is the green pigment in plant which is responsible
for photosynthesis. Organometallic compounds of magnesium have also been isolated, the
grignard reagents are the most important organometallic compounds of Mg and are probably
the most extensively used of all organometallic reagents. Grignard reagents contain a variety
of chemical species inter linked by mobile equilibrium whose position depends critically on
at least five factors: 100
(i) the stearic and electronic nature of the alkyl (aryl) group R (ii) the
nature of the halogen X (size, electron-donor power etc) (iii) the nature of the solvent (Et2O,
THF, benzene etc) (iv) The concentration and (v) the temperature of the species present. It
may also depend on the presence of trace impurities such as H2O or O2.101
Grignard reagents
are normally prepared by the slow addition of the organic halide to a stirred suspension of
magnesium turnings in the appropriate solvent and with rigorous exclusion of air and
moisture. The reaction which usually begins slowly after an induction period can be initiated
by addition of a small crystal of iodine and this penetrates the protective layer of oxide
(hydroxide) on the surface of the metal. The order of reactivity of RX is I>Br >Cl and alkyl
>aryl.102
. They have been applied in the synthesis of alcohols, aldehydes, ketones ,carboxylic
acids, esters and amides and are probably the most versatile reagents for constructing C-C
bonds by carbonion (free-radical) mechanism103
A related class of compounds, the alky-
magnesium alkoxides can also be formed by the reaction of MgR2 with an alcohol or ketone
or by reaction of Mg metal with the appropriate alcohol and alkyl chlorides in
methylcyclohexane solvent104-105
.
34
4M gEt2 + 4ButO H (E tM gDBut)4 +4C
2H
6
2M gM e2 + 2ph
2CO
Et2O
(M e M gO CM ph2
.E t2O )
2
2.62 Review of Previous Works Done on Magnesium Chelates of β-diketones.
Majority of the works reported on the Mg(II) complexes of 1,3-diketones are based on
the concentration and extraction of metals using 4-acylpyrazolone ligands 106-107
. Bukowky
and others reported the extraction of Mg(II) Ion from neutral solution by an 1so-arylalcohol
solution of HPMBP 106
. The extraction was quantitative when oxygen containing solvents
were used and the medium weakly alkaline.68
Mirza 107
in 1970, reported the preparation of 28
Mg in a nuclear reactor and stated a procedure for extraction of micro amounts of 28
Mg from
a mixture of radioactive materials. There are also reports on the structure and IR spectral
studies of magnesium complexes of 4-acyl pyrazolones in literature. Okafor26
has reported
the synthesis and infrared spectral studies of the magnesium chelate of 1-phenyl-3-methyl-4-
trifluoroacetyl pyrazolones. He observed from analytical results that the complex has the
molecular formula M(PMTFP)2. 2H2O( where M=Magnesium and PMTFP is the ligand
anion) with negligible molar conductance values in DMF solution showing that the complex
was neutral. He also reported that the Benzoyl derivative of the 4-acylpyrazolone gave a
white colored complex with magnesium (96)
and used proton NMR spectral studies to deduce
the number of associated water. The infrared spectral data showed a shift in the carbonyl
stretching frequency from 1640cm-1
in the ligand to 1635cm-1
in the metal complex showing
that there was complexation through the C=O of the chelate ring.
2.70 Chemistry of Cobalt
Cobalt is a very tough metal with high tensile strength. it is relatively unreactive in
H2O, H2 or N2, though it reacts with steam forming CoO. It is oxidized when heated in air and
burns at white heat to CO3O4. Co dissolves slowly in dilute acid but rendered passive by
35
concentrated HNO3. It combines readily with halogens and at elevated temperature with S, C,
P, As and Sn.2 The most common oxidation states of cobalt are the +II and+ III, [Co(H2O)6]
2+
and Co(H2O)6]3+
are both known but the later is a strong oxidizing agent and in aqueous
solution, it is acidic. The +Ill oxidation state is the most prolific oxidation state of cobalt,
providing a variety of kinetically inert complexes. These complexes are virtually low spin
octahedral complexes. A major stabilizing influence being the high CFSE associated with the
t2g6
configuration, the maximum possible for any dx configuration. Even [Co(H2O)6]
3+ is a
low spin complex, but it is such a strong oxidizing agent that it is unstable in aqueous
solution as mentioned earlier. Only a few simple salt hydrates such as the blue Co2(SO4)3
.18H2O and MCo(SO4)2 .12H2O (M=K, Rb, Cs, NH4) which contain the hexa aquo ion and
CoF3. 3½H2O can be isolated.109
As a result of the kinetically inert nature of cobalt (III)
complexes, they are prepared by addition of the ligands to an aqueous solution of cobalt (II)
salt and the cobalt (II) complex formed is oxidized by some convenient oxidant in the
presence of a catalyst such as active charcoal 110
. Compounds of cobalt (III) formed with N-
donor ligand like the NO2 ion are (Na3[Co(NO2)6]), orange sodium cobaltinitrite which is
used in aqueous solution for the quantitative precipitation of K+ as K3(Co(NO2)6] in classical
analysis. Treatment of this compound with flourine yields K3(CoF6) whose anion is notable
not only as the only hexa halogeno complex of cobalt(III) but also for being high spin and
hence paramagnetic, with a magnetic moment at room temperature of nearly 5.8BM. The
complexes of cobalt (III) with O-donor ligands are generally less stable than those of with N-
donors, although the dark green Co(acac)2 and M3[Co(C2O4)3 and M3[Co(C2O4)3] complexes
formed from the chelating ligands acetylacetonate and oxalate are stable. Other caboxylate
complexes such as those of acetate are however less stable but are involved in the catalysis of
a number of oxidation reactions by Co11
carboxylates.112
The chemistry of cobalt(III)
complexes is similar to those of chromium(III) but a noticeable difference between the two is
the smaller susceptibility of the former to hydrolysis, though limited hydrolysis leading to
36
polynuclear cobaltammines with bridging OH-groups. Other common bridging groups are
NH2-, NH3
2- and NO2
- and singly, doubly and triply bridged species are known such as
the bright b lue [(NH3)
5 Co-NH
2-Co(NH
3)
5]5+
garnet red- [NH3)
4Co
O H
O HCo (NH
3)
4]4+ and red [(NH
3)
3O H
O H
Co Co
NH2
(NH3)
3]3+
But the most interesting of the poly nuclear complexes are those containing O-O bridges,113
for example, the brown [NH35 Co-O2-Co(NH3)5]4+
green paramagnetic [(NH3)5 Co-O2-Co(NH3)5]5-
, red [(NH3)4 Co(µ-NH2)-µ-O2) Co(NH3)4]4-
and
brown[(NH3)4 Co(µ-NH2)-µ-O2) Co(NH3)4]3+
The +II oxidation state of cobalt gives rise to simple salts with all the common anions and
they are readily obtained as hydrates from aqueous solutions. The cobalt (II) carboxylates
such as the red acetate, Co(O2CMe)2 .4H2O are known.They are monomeric and in some
cases the carboxylate ligands are unidentate 114
. The acetate is employed in the production of
catalyst used in certain organic oxidations and also as a drying agent in oil based paints and
varnishes115
. Many of the hydrated salts and their aqueous solutions contain the octahedral
pink [Co(H2O)6]2+
, ion and bidentate N-donor ligands such as en, bipy, phen and
octahedral cationic complexes [Co[L-L)3]3+
which are much more stable to oxidation than is
hexamine [Co(NH3)6]2+
acetyl Acetonate (Acac) yields the orange [Co(acac)2H2O)2] which
has the trans octahedral structure and can be dehydrated to Co(acac)2.This attains octahedral
coordination by forming the tetrameric species. [Co(acac)2]4]. Tetrahedral complexes are also
common being formed more readily with cobalt(II) than with the cation of any other truly
transition element (excluding ZnII). Thus in aqueous solutions containing [Co(H2O)6]
2+ and in
acetic acid the tetrahedral [Co(O2CMe)4]2-
occurs. Anionic complexes [CoX4]2-
are formed
with the unidentate ligands X=Cl, Br, I, SCN and OH and a whole series of complexes
[CoL2X2] (L=ligand with group 15 donor atom X=halide, NCS) has been prepared in which
37
both stereochemistries are found116
. The most obvious distinction between the octahedral and
tetrahedral compounds is that in general, the former are pink to violet in colour whereas the
later are blue as exemplified by the well known equilibrium.
[Co(H2O )
6]2+ + 4C l
-[CoC l
4]2 + 6H
20
-
pink blue
Square planar complexes of cobalt(II) are also well documented and including
[Co(phthalocyanine)] and [Co(CN)4]- as well as [Co(salen)] and complexes with other Schiff
bases.117
These complexes are a invariably low spin with magnetic moments at room
temperature in the range of 2.1-2.9BM. Indicating the presence of an unpaired electron. They
are primarily of interest because of their oxygen-carrying properties, The uptake of dioxygen
which bonds in the bent configuration C o O
O
is accompanied by the attachment of a
solvent molecule trans to the O2 and the retention of the single unpaired electron. There is
fairly general agreement, based on electron spin resonance evidence, that electron transfer
from metal to O2 occurs just as in the bridged complexes producing a situation close to the
extreme represented by low-spin CoIII
attached to a super oxide ion O2-. The opposite
extreme represented by CoII-O2, implies that the unpaired electron resides on the metal with
the dioxygen being rendered diamagnetic by the consequent spin pair. However, the extent of
the electron transfer is probably determined by the nature of the ligand trans to the O2118
.
The five coordinate OH compounds which have been characterized included [CoBr-
NC2H4NMe2)3]+
which is a high spin with 3 unpaired electrons and is trigonal bipyramidal
(imposed by “tripod” ligand) and [Co(CN)5]3-
which is a low spin with an unpaired electron
and is square pyramidal. The absence of a simple hexacyano complex is significant as it
seems to be generally the case that ligands such as CN- which are expected to induce spin
paring favor a coordination number 4 for CoII rather than 6; The planar [CoCdiars)2(ClO4) is
38
a further illustration of this.Presumably Jahn-Teller distortion, which is anticipated for the
low spin t2g6 and eg
1 configuration is largely responsible.
119
2.71 Previous Work Done on Cobalt with β-diketones.
Recently, Pamar and Teraiya in (2009)
120 synthesized and characterized the cobalt complexes
of some 5-pyrazolone based Schiff-base ligands and observed that the OH stretching
frequencies of the free ligands is displaced to the 3350cm-1
- 2800cm-1
region due to the
internal hydrogen bonding of the OH with N=C.They also assigned displacement of the C-O
stretch (1305-1320cm-1
) of the ligand to a higher (1310-1330cm-1
) in the complex to the
participation of the 5-OH of the pyrazolone in chelation. The far infrared spectra of the metal
chelates showed bands at 490-500cm-1
and 400-415cm-1
, indicative of the Co-N vibration of
azomethine nitrogen consistent with octahedral geometry.
The cobalt complexes of 4- adipoyl and 4-sebacoyl derivatives of bis (1-phenyl-3-methyl
pyrazolone have been characterized by Uzoukwu and others 122
and assigned electronic data
values of max =244nm for 4-adipoyl and 250nm for the 4-sebacoyl derivatives. They
ascribed the sharp infrared peaks occurring at 448cm-1
for the 4-adipoly derivative and
474cm-1
for the 4-sebacoyl derivative to the Co-O asymmetric stretching frequency. They
concluded that cobalt (II) ion formed a dimeric complex Co(SP)2 with the 4-sebacoyl
derivative and a monomeric complex with the 4-adipoyl derivative. The cobalt (II) complexes
of some other derivatives of the 4-acyl pyrazolones have been synthesized,87
and the
microanalytical data on the complexes showed that the mode of interaction between Co2+
and
the ligands is in the mole ratio of 1:2. These complexes are bischelates, associated with two
molecules of water of crystallization from the aqueous medium. Okafor has also worked on
the cobalt (II) complexes of benzoyl (96)
, and triflouro acetyl 28
derivatives of the 4-acyl
pyrazolones and characcterised them by elemental, electronic ,infrared spectral, proton and
carbon 13 NMR spectral studies. Some other workers 121,122
have equally studied the
39
synthesis and characterization of Cu (II) complexes of some other non pyrazolone based
derivative of the -diketone family.
2.80: The chemistry of copper
The name copper and the symbol Cu are derived from eascyprium (Later cuprum) since it
was from Cyprus that the Romans first obtained the copper metal. It is a very strong and
stable metal, Unreactive with hydrogen, but the reddish brown precipitate obtained when
aqueous CuSO4 is reduced by hypophosphoric acid (H3PO2) is largely CuH. They form two
oxides Cu2O (yellow or red) and CuO (black) when the metal is heated in air or O2, Cu2O
being favoured by high temperature .125
Copper is also attacked by sulphur and halogens to
form Cus, the more stable Cu2S, CuCl2 and CuBr2 etc. The reactions of copper metal are
generally assisted by the presence of air. Non-oxidizing acids have little effect but Conc
H2SO4, and Conc HNO3 can dissolve the metal 126
.
Copper exists in two common oxidation states, the +1 (cuprous) and +2 (cupric)
oxidation states. Because the oxidation potential for the Cu+/Cu
2+ half reactions is less
negative than for Cu/Cu+ half reactions, any oxidizing agent strong enough to oxidize copper
to copper atom is also able to oxidize the copper(I) to copper (II) ion.
Cu(S )
Cu+(aq)
+ e -E
o= 0.52v
Cu+ (aq) Cu2+ -E
o0.15(aq)
+ ev = 0.15v
Cu(I) forms diamagnetic compounds coordinated to polarized ligands easily in aqueous
solution. Cu(1) Ion is very unstable with respect to disproportionation.
2Cu(I) Cu(II) + Cus
Nevertheless, CuI
can be stabilized either in compound of very low solubility or by
complexing with ligands having π-acceptor character. Its solutions in MeCN are stable and
40
electrochemical oxidation of the metal in this solvent provides a convenient preparative route
127. Tetrahedral complexes such as (Cu(CN)4]
3- [Cu(py)4]
+ and [Cu(L-L)2 e.g L-L=bipy,
phenl) are known, but lower coordination numbers are possible such as in linear (CuCl2)-
formed when CuCl is dissolved in hydrochloric acid and in K[(Cu(CN)2] which solid
contains a trigonal, almost planar Cu(CN)2 units linked in polymeric chain.The + (II)
oxidation state of copper provides by far the most familiar and extensive chemistry of copper,
forming simple salts with most anions except CN and I- which instead, form covalent Cu
I
compounds which are insoluble in water. The salts are predominantly water-soluble, the blue
color of their solutions arising from the [Cu(H2O))6]2+
ions and they frequently crystallize as
hydrates 128
. The most common coordination number of copper(II) are 4,5 and 6, but regular
geometries are rare and the distinction between square-planar and tetragonally distorted
octahedral coordination is generally not easily made. The reason for this is ascribed to the
Jahn- Teller effect arising from the unequal occupation of the eg pair of orbitals (dz2 and dx
2-
y2) when a d
9 ion is subjected to an octahedral crystal field. Occasionally as in solid KAlCuF6
for instance, this results in a compression of the octahedron ie “2+4” coordination (2 short
and 4 long bonds).129
The usual result however is an elongation of the octahedron ie “4+2”
coordination. (4 short and 2 long bonds) as is expected if the metals dz2 orbital is filled and
its dx2-y
2 is half filled. In its most extreme form, it is equivalent to the complete loss of the
axial ligand leaving a square planar complex. A few 5-coordinate complexes of copper (II)
such as [Cu(bip)3]+ in its perchlorate has been described as square pyramidal or distorted
octahedral130
. The Macro cyclic N-donor, phthalocyanine forms a square-planar complex and
its substituted derivatives are used to produce a range of blue to green pigments, which are
thermally stable to over 5000C and are widely used in inks, paints and plastics. In alkaline
solutions biuret, HN(CONH2)2 reacts with copper(II) sulfate to give a characteristic violet
color due to the formation of the complexes (Cu2(µ-OH)2 (NH CoNH CoNH)4)2-
. This is the
basis for the biuret test in which an excess of NaOH solution is added to the unknown
41
material together with a little CuSO4 solution, a violet color indicates the presence of protein
or other compounds containing a peptide linkage.
Copper(II) also forms stable complexes with O-donor ligands. In addition to the hexaquo Ion,
the square planar -diketonates such as [Cu(acac)2] (which can be precipitated from
aqueous solution and recrystalized from non aqueous solvents) and tatrate complexes used in
fehling’s test are well known. 131
2.81:Previous work on the Copper Chelates of β-diketones
Most of the work done on the copper complexes of 4-acyl pyrazolones were on the extraction
and concentration of the metal from aqueous and acidic solution. 23,24,132,133,134
Zolotov others
133 extracted a number of copper chelates from aqueous solutions and deduced from micro
analytical data that the mode of interaction between Cu2+
and 4-acyl pyrazolones is in the
metal ligand mole ratio of 1:2 and reported the formation of dirty green complexes.
Hassany24
reported the extraction of copper complexes with similar metal ligand composition
and concluded that all the complexes were hydrophobic and are soluble in chloroform,
dioxane ,DMF and DMSO. Akama and others23
also extracted copper(II) ions from aqueous
solutions and reported that the formation of a stable and hydrophobic metal complex were
one of the properties responsible for the efficient extraction of Cu2+
ions from aqueous and
acidic solutions. The thermal decomposition of copper complexes of some-1-phenyl-3-
methyl-4-acyl pyrazolones in air were studied in 1995 and it was reported that the melting
point of the complexes decreases linearly in increasing molecular weight 137
In the last two decades, a lot of information have appeared in literature on the spectroscopic
properties of copper(II) complexes of 1-phenyl-3-methal-4-acyl pyrazones-5-ones and their
derivatives. The Cu(II) complexes of 4-adipoyl and 4-sebacoyl derivatives of bis (1-phenyl-3-
methyl pyrazol-5-one) have been synthesized and characterized 87
. The spectral data obtained
42
showed that the Cu(II) chelate of the 4-adipoyl derivative (H2Adp) existed as a -diketone
while the 4-sebacoyl derivative(H2SP) existed keto-enol tautomer. Though subsequently the
4-adipoyl derivative underwent rearrangement to the ketoenol tautomer.
Okafor 96
synthesized the copper(II) complex of 1-phenyl-3-methyl-4-benzoyl
pyrazolone, characterized it by infrared spectral studies and reported a 471cm-1
M-O
stretching frequency band for the complex. Uzoukwu and others138,139
in 1992 studied the
electronic and vibration properties of a series of copper complexes of some 1-phenyl -3-
methyl 4-acyl pyrazolone-5 and observed that the complexes in chloroform had two bands in
the UV region near 251nm (E2500) and 294nm (E 2000). Each of these bands suffered a
bathochromic shift by 1-5nm with respect to identical bands in the UV spectrum of the ligand
and these he ascribed to intra ligand -* transitions. They concluded that the -bonding
system of the ligand is almost intact in the ligand anion of the complex, thus making it
possible for the Cu2+
to form a bond with the ligand by the displacement of the proton of
the OH group of the ketoenol tautomer of the 4-acyl pyrazolone by the Cu2+
Ion. Some other
workers140
corroborated this assertion using infrared evidence which showed a
bathochromic shift of the asymmetric stretching frequencies of the C=O group of the ligand
on complex formation. The infrared data further suggested that the stability of the Cu-O
bond in the complexes decreases with increase in carbon chain of the 4-acyl substituent while
the reverse is the case for the Cu-O of the Cu=O-Cu bonding system. Hence a magnetic
moment of between 1.175-1:82B.M at 298K was suggested for all the complexes.
2.90: Chemistry of Zinc
Zinc occurs in nature in the form of zinc sulphide (which is known as Zinc blende and
ZnCO3 (Calamine). It is a silvery solid with blush lustre when freshly formed. Zinc tarnishes
quickly in moist air and combines with oxygen, sulphur, phosphorus and the halogen on
being heated. Zinc dissolves in non oxidizing acids to liberate hydrogen and oxidizing acids
43
to form a variety of oxides 141
. In view of the stability of the filled d shell, the Zinc element
shows a few of the characteristic properties of the transition metals despite their position in
the d block of the periodic table. Thus Zinc show similarities with the main group metal
magnesium, many of their compounds being isomorphous and displays the class-a
characteristics of complexing readily with O-donor ligands. 142
On the other hand Zinc has a
much greater tendency than magnesium to form covalent compounds, and it resembles the
transition metals in forming stable complexes not only with O-donor ligand but with N- and
S-donor ligand and with halides and CN-143
Most compounds of Zn2+
are diamagnetic and
like those of Mg11
are colorless.The almost invariable oxidation state of Zinc is + 2 and it
forms salts of different compounds in form of oxides, halides and chacogenides.144
Salts of
other anions are also known, oxo salts are often isomorphous with those of Mg11
but with
lower thermal stabilities. The carbonates, nitrates and sulphates all decompose to the oxides
on heating. Several zinc salts such as the nitrates, perchloates and sulfates are very soluble in
water and form mostly one hydrate salts. [Zn (H2O)6]2+
is probably the predominant aquo
specie in solutions of Zinc salts. Aqueous solutions are appreciably hydrolyzed to species
such as [M(OH)(H2O)x]+ and M2(OH)(H2O)x]
3+ and a basic salt such as ZnCO3.2H2O
Zn(OH)2 . 2H2O can be precipitated. Distillation of Zinc acetate under reduced pressure
yields a crystalline basic acetate [Zn4O(OCO Me)6]. The molecular structure of this
compound consist of an oxygen atom surrounded by a tetrahedron of Zn atoms bridged across
each edge by acetates. It is isomorphous with the basic acetate of beryllium but in contrast,
the Zn2+
compounds hydrolyses rapidly in water. The coordination chemistry of Zinc(II)
although less extensive than for preceding transition metals is still appreciable. It does not
form stable flouro complexes but with the other halides it forms complex anions [MX3]- and
[MX4]2-.
Tetrahedral complexes are the most common type and are formed with a variety of
O-donor ligands, more stable ones with N-donor ligands such as NH3 and amines. Some of
the apparently 3-coordinate complexes have higher coordination numbers because of the
44
aquation or association but no doubt because the ligand is bulky. 2- coordinated Zn occurs in
[ZnN.(CMe3)[SiMe3]2, the first homoleptic Zinc amide to be structurally characterized 145,146
.
Complexes of higher coordination numbers are often in equilibrium with the
tetrahedral form and may be isolated by increasing the ligand concentration or by adding
large counter ions e.g [M(NH3)6]2+
, [M(en)3]2+
or [M(bipy)3]2+
.With acetylacetone, Zinc
achieves both 5 and 6 coordination by trimerizing to [Zn(acac)2]3. Five coordination is also
found in adducts such as the distorted trigonal bipyramidal [Zn(acac)2 (H2O)] and [Zn
(glycinate)2 H2O)2] while the hydrazinium sulfate (N2H5)2 Zn(SO4)2 contains 6-coordinated
Zinc. This is isomorphous with Cr(II) compounds and in the crystalline form consists of
chains of ZnII bridged by SO4
2- Ions with each Zn
2+ additionally coordinated to two trans
N2H5+ ions. The Zinc porphyrin complex [Zn(porph) THF] (porph=Meso-tetraphenyl
tetrabenzo porphyrin) is approximately square pyramidal with THF at its apex. Being
somewhat flexible, the porphyrin is distorted into a saddle shape, and displaced above its
mean plane . 147
Compounds with coordination numbers higher than 6 are rare and in some
cases are known to involve chelating NO3- ions which not only have a small bite but may also
be coordinated asymmetrically so that the coordination number is not well defined1.
2.91:Previous Work Done on Zinc(11) Chelates of β-diketones
A good number of publications have appeared in literature on the Zn(II) chelates of
the 4-acyl pyrazolones and their derivatives18,28,87,94,96
Uzoukwu in 1992 synthesized some
derivatives of the 4-acyl pyrazolones and used them in extraction of Zn(II) ions from acid
media.94
The spectroscopic data obtained from UV, IR and HNMR analysis showed that the
stability of both CO-M and C=O bonding system did not follow any trend, with respect to
the nature of the 4-acyl substituent; unlike in similar reports14, 138
. However he observed that
the aryl substituted 4-acyl derivatives had higher νas C=O than those of the alkyl substituted
4-acyl derivatives. The Zn(II)complex of 4-benzoyl pyrazolone has also been synthesized96
45
and micro analytical data predicted a molecular formula of Zn(PMBP)2 .YC2H5 indicative of
the presence of coordinated solvent molecules . Careful interaction of the protons signals in
the proton Nmr spectra revealed one molecule of C2H5OH associated with the molecules of
the metal complex. Ozaki and other148
reported the solvent extraction of Zinc with 1-(2-
chloro phenyl) 3-methyl-4-aryl pyrazolone, while Umetani and Matsui 149,150
reported the
procedure for extracting micro amounts of Zn(II) and cadmium with 4-Benzoyl -3-methyl-1-
phenyl-5-pyrazolone and Quaternary Ammonium salts dissolved in organic solvents. They
also reported the liquid- liquid distribution of 4-acyl-3-methyl-1-phenyl 5-pyrazolon and their
Zinc complexes and stated that the extraction was quantitative when oxygen containing
solvents were used and the medium weakly alkaline.151
2.92: SPECTROSCOPIC TECHNIQUES USED IN THE STUDY OF LIGANDS AND
METAL COMPLEXES
2.93 Ultraviolet/ Electronic Spectroscopy
Electronic spectra of metal ions and complexes are observed in the visible and
Ultraviolet regions of the electromagnetic spectra.152
This type of absorption
spectroscopy shows the particular wavelengths of light absorbed, that is the particular
amount of energy required to promote an electron from one energy level to a higher
energy . The visible and ultraviolet spectra of compounds are associated with
transitions in electronic energy levels. The transitions are generally between a
bonding or lone pair orbital and an unfilled non-bonding or anti-bonding orbital. The
wave length of the absorption is the measure of the separation of the energy levels of
the orbitals concerned 153
. The highest energy separation is found when electrons in
bonds are excited, giving rise to absorption in the 120-20nm (1nm=10-
7cm=10Ǻ=1mµ) range. This range known as the vacuum Ultraviolet, (since air must
be excluded from the instrument) is both difficult to measure and relatively
46
uninformative. Above 200nm, however excitation of electrons from p, d , -orbitals
and particularly, -conjugated systems gives rise to readily measured and informative
spectra. The interpretation of the spectra provides a most useful tool for the
description and understanding of the energy levels present.
2.94: Infrared Spectroscopy
The infrared radiation refers broadly to that part of the electromagnetic spectrum
between the visible microwave regions and the far infrared regions of the electromagnetic
spectrum. Of greatest practical use to the chemist is the limited portion between 4000cm-1
at
high frequency end to 400cm-1
at the low frequency end, though there has been some
interest in the near IR (14,290-4000cm-1
) and the far IR regions (700-200cm-1
). 154
The infrared spectrophotometer consists of a source of infrared light, emitting radiation
throughout the whole frequency range of the instrument. This light is split into two beams of
equal intensity, and one beam is arranged to pass through the sample to be examined. If the
frequency of vibration of the sample molecule falls within the range of the instrument, the
molecule may absorb energy of this frequency from the light. The spectrum is therefore,
scanned by comparing the intensity of the two beams after one has passed through the sample
to be examined. The wavelength range, above which the comparism is made, is spread out in
the usual way with a prism or grating. The whole operation is done automatically in such a
way that the usual finished spectrum consists of a chart showing downward peaks,
corresponding to absorption plotted against wavelength or frequency to allow for variations
in the spectrometer. Spectras are often calibrated against accurately known band of the
spectrum of polystyrene, the peaks of one or more of these bands being superimposed on the
spectrum which is to be taken.[154]
Compounds may be examined in the vapor phase, as pure
liquids in solution and in the solid state. These molecules can absorb radiation energy from
the region stated above and convert them into molecular vibrations resulting in energy
47
vibrations patterns known as the infrared spectrum.155
Some structural groups of atoms give
rise to vibrations bands at or near the same frequency regardless of the structure of the
molecules. The theoretical number of fundamental vibrations (absorption frequencies) will
seldomly be observed because overtones (multiples of a given frequency) and combination
tones (sum of two other vibrations) increase the number of bands whereas other phenomena
reduce the number of bands156
. The following will reduce the theoretical number of bands:
a. Fundamental frequencies that fall outside of the 4000-400cm-1
region
b. Fundamental bands that are too weak to be observed
c. Fundamental vibrations that are so close that they coalesce
d. The occurrence of a degenerate bands from several absorptions of the same frequency
in higher symmetrical molecules.
e. The failure of certain fundamental vibration to appear in the IR because of the lack
of changes in molecular dipole.
Essentially, these properties help a chemist in obtaining some usefull structural
information by simple inspection and reference to generalized chart of characteristic
group frequencies 153
48
CHAPTER THREE
3.0 EXPERIMENTAL
3.1 Laboratory Apparati/ Equipment
(1) One litre 3-necked quick fit flask
(2) One litre sized electro heating mantle
(3) Fisher Johns melting point apparatus
(4) Reflux condensers
(5) Fractionating adaptors
(6) 3600C quick fit thermometer
(7) Gallenkamp mechanical stirrer
(8) EB 3A Vacum pump
(9) Dessicators
10. Seperatory and dropping funnels
11. Electronic metler balance
12. (Water bath) electric thermostated
13. IR spectrophotometer
14. Jenway 6405 Uv spectrophotometer
15. Jenway Conductivity meter
16. Wat-Horytont Electric stirrer
3.2: Reagents
Most of the reagents used were of analytical grade and were used without further
purification.
(1) 1-phenyl-3-methyl-pyrazolon-5-from Fluka
(2) Dioxane manufactured by Hopkins and Williams
49
(3) Anhydrous calcium hydroxide from BDH
(4) Calcium chloride from BDH
(5) Phosphorus pentachloride from BDH
(6) Acetyl chloride from sigma Aldrich
(7) Hexanoyl chloride from sigma Aldrich
(8) Benzoyl chloride form sigma Aldrich
(9) Butyryl chloride from sigma Aldrich
(10) Palmitoyl chloride from Fluka
(11) Magnesium acetate from Fluka
(13) Zinc acetate from Merck
(14) Copper Acetate, from Merck
(15) Cobalt (II) Chloride from Merck
(16) Hydrochloric acid Manufactured by sigma-Aldrich
(17) 95% ethanol from sigma-Aldrich
(18) Methanol from sigma-Aldrich
(20) N-Hexane manufactured BDH
(21) Acetone manufacture by Sigma-Aldrich
(22) Benzene manufactured by BDH
(23) Diethyl ether manufactured by BDH
50
(24) Dimethyl formaide (DMF) from Fluka
(25) Tetra hydro furan (THF) from East Anglia Chemicals
(26) Dimethylsulfoxide (DMSO) from BDH
3.30 Synthesis of 1-phenyl-3-methyl-4-acyl pyrazol-5-ones
3.31 Synthesis of 1-phenyl-3-methyl-4-Acetyl pyrazol-5-one (HPMAP)
The synthesis was carried out using a modified Jensen’s method11
. 8.5g 1-phenyl-3-
methyl-pyrazol-5-one (HPMP) was dissolved in 100cm3 of dioxane in a 1 litre three
necked flask fitted with an electric stirrer and a reflux condenser by warming. The
dioxane solution was allowed to cool to room temperature before 10g of Ca(OH)2 was
added and the mixture stirred, No heat was applied 3.5cm3 of acetyl chloride from a quick
fit dropping funnel was added dropwise within 3 minutes. The reaction was exothermic,
the reaction mixture was stirred for I hour without applying any heat and the resulting
orange mixture was then poured into a chilled 3M HCl (500cm3) solution with vigorous
stirring. The reaction mixture was later kept in a refrigerator until pinkish crystals
separated. They were filtered off, washed with water and recrystallized from aqueous
ethanol to give white crystals. The crystals were dried in air and stored in a desiccator.
3.32 Synthesis of 1-phenyl-3-methyl-4-Benzoyl pyrazol-5-one (HPMBP)
7.5g 1-phenyl-3-methyl-pyrazol-5-one (HPMP) was dissolved in 100cm3 of dioxane
in a I litre three necked flask fitted with an electric stirrer and a reflux condenser by
warming. The Dioxane solution was allowed to cool to room temperature before 10g of
Ca(OH)2 was added. The mixture was stirred with no application of heat before 5cm3 of
benzoyl chloride from a quick fit dropping funnel was added dropwise within 3 minutes.
The reaction mixture became a thick yellow paste and the temperature increased during
the first few minutes. Stirring of the mixture was continued with low heat application for
51
1 hour. The resulting orange mixture was poured into chilled 3M HCL (300cm3) with
stirring to decompose the calcium complex. Stirring was continued until an orange brown
solid precipitated from the solution. This was filtered off, washed with water and
recrystallized from aqueous ethanol to give white crystals.
3.33 Synthesis of 1-phenyl-3-methyl-4-Propionyl pyrazol-5-one (HPMPRP)
The synthesis was carried out as described above for HPMBP from 7.5g HPMP and
4cm3 of propionyl chloride.
3.34 Synthesis of 1-phenyl-3-methyl-4-Butyryl pyrazol-5-one (HPMBUP)
The synthesis was carried out as described for HPMBP from 8.5g of HPMP and
5.2cm3 of butyryl chloride.
3.35 :Synthesis of 1-phenyl-3-melthyl-4-Hexanoyl pyazol-5-one
The synthesis was carried out as described for HPMBP synthesis using 8.5g of HPMP
and 7cm3 of capyroyl chloride.
3.36:Synthesis of 1-phenyl-3-methyl-4-palmitoyl-pyazol-5-one (HPMPP)
The synthesis was carried out as described for HPMBP synthesis from 8.5g of HPMP
and 15cm3 of palmitoyl chloride.
3.40: Synthesis of metal-1-phenyl-3-methyl-4-acyl-pyrazolonates
3.41: Synthesis of 1-phenyl-3-methyl-4-actyl-5-pyrazolonato magnesium II Complex
Mg(PMAP)2. 2H2O
2.1623g 1-phenyl-3-methyl-4-acetyl-pyrazolone-5 (about10mM) was dissolved in
25ml 95% ethanol by warming at a temperature of 450C In a 100cm
3 beaker. This was
added to a solution of the magnesium (II) Acetate containing 5mM, 1.072g in 20cm3 of
52
distilled water drop wise with stirring until the complex precipitated out of solution.The
dirty white precipitate was filtered under suction and washed with aqueous ethanol (I/I),
dried in air and stored in a desiccator over fused calcium chloride. The method above was
used for the synthesis of 1-phenyl-3-methyl-4 butyryl pyrazolonato magnesium (II)
complex Mg(PMBUP)2 from 1.027g of 1-phenyl-3-methyl 4-butyryl pyrazolone and
2.144g of magnesium acetate Mg(CH3COO)2; for the synthesis of 1-phenyl 3-methyl-4-
Benzoyl pyrazolonato magnesium (II) complex, Mg(PMBP)2.2H2O from 2.783gof
HPMBP and 1.027g of Mg(CH3COO)2; for the synthesis of 1-phenyl 3-methyl-4-
propionyl pyrazolonato magnesium (II) complex dihydrate Mg (PMPRP)2 2H2O using
2.303g of HPMPRP and 1.027g of Mg (CH3COO)3; for the synthesis of 1-phenyl-3-
methyl-4-capyroyl-5-pyrazolonato magnesium (II) complex dihydrate from 2.723g of
HPMCP and 1.0217 of Mg(CH3COO)2 ; for the synthesis of 1-phenyl-3-methyl- 4-
palmitoyl-5-pyrazolonato magnesium(ii) dihydrate (Mg(PMPP)2.2H2O) from 4.126g of
HPMPP and 1.027g of Mg(CH3 COO)2.
3.42: Synthesis of 1-phenyl-3-methyl 4-acetyl-5-pyrazolonato copper (II) Complex.
2.163g(10mM) of 1-phenyl-3-methyl-4-acetyl-4-pyrazolone-5 was accurately
weighed and dissolved in 95% ethanol (50ml) and warmed to about 400C in a 100cm
3
beaker and 0.9082g(5mM) of copper(II) acetate was weighed and dissolved in 20Cm3
of
distilled water and added to the ethanolic solution of the ligand at 450C and stirred until a
dark green precipitate of Cu(PMAP)2 .2H2O was obtained. The precipitate was filtered
under suction, washed well with aqueous ethanol (1/1), dried in air before storing in a
desiccator over fused calcium chloride.
The method described above was used for the synthesis of 4-acyl-5-pyrazolonato
copper (II) complexes stated below. 1-phenyl-3-methyl 4-benzoyl-5-pyrazolonato copper
(II) complex Cu(PMBP)2 .2H2O was synthesized from 0.908g of Cu(CH3COO)2. 2H2O
53
and 2.783g of HPMBP, 1-phenyl-3-methyl 4-Butyryl 5-pyrazolonato copper (II) complex
Cu(PMBUP)2 2H2O was synthesized from 0.908g of Cu(CH3COO)2 and 2.443g of
HPMBUP, 1-phenyl-methyl-4-propionyl-5-pyrazolonato copper(II) complex
Cu(PMPRP)2 .2H2O synthesized from 0.908g of Cu(CH3COO)2 and 2.303g of
HPMPRP.1-phenyl -3-methyl-4-capyroyl pyrazolonato copper(II) complex dihydrate
(Cu(PMCP)2 .2H2O was synthesized from 0.908g Cu(CH3COO)2 and 2.723g of HPMCP;
1-phenyl-3-methyl-4-palmitoyl-5-pyrazolonato copper (II) complex dihydrate
Cu(PMPP)2.2H2O was synthesized from 0.908g of Cu(CH3COO)2 and 4.126g of HPMPP.
3.43: Synthesis of 1-phenyl-3-methyl-4-acetyl-5-pyrazolonato cobalt (II) complex
1.189g (5mM) of cobalt (II) chloride was accurately weighed and dissolved in 75ml
95% ethanol with warming and slowly added with stirring to a hot ethanolic solution of
the ligand containing 2.163g (10mM) of 1-phenyl-3-methyl-4-acetyl pyrazolone in 75ml
of 95% ethanol. The pinkish orange precipitate formed was filtered under suction, washed
with aqueous ethanol (1/1), dried in air before storing in a desiccator over fused calcium
chloride.
The method described above was used for the synthesis of 1-phenyl-3-methyl-4-
benzoyl-5-pyrazolonato cobalt (II) Co(PMBP)2. 2H2O from 1.189g of Cobalt(II) chloride
and 2.7832g of HPMBP, 1-phenyl-3-methyl-4-Butyryl-5-pyrazolonato cobalt(II) complex
Co(PMBUP)2 2H2O from 0.595g of CoCl2 and 1.221g of HPMBUP, 1-phenyl-3-methyl-
4-propionyl -5-pyrazolonato cobalt (II) complex Co(PMPRP)2 .2H2O from 0.297g of
CoCl2 and 0.576g of HPMPRP, 1-phenyl-3-methyl-4-capyroyl-5-pyrazolonato cobalt (II)
complex Co(PMCP)2. 2H2O from 0.595g of CoCl2 and 1.362g of HPMCP, 1-phenyl-3-
methyl-4-palmitoyl-5-pyrazolonato cobalt (II) complex dihydrate Co(PMPP)2. 2H2O,
from 0.149g of CoCl2 and 0.516g of HPMPP.
54
3.44: Synthesis of 1-phenyl-3-methyl-4-Acetyl-5-pyrazolonato Zinc(II) complex.
1-phenyl-3-methyl-4-acetyl pyrazolone-5(1.082g) 10mM was accurately weighed and
dissolved in 50cm3 of 95% ethanol by warming at a temperature of 45
0C, this was added
with stirring to a solution of the Zinc metal containing 0.549g of Zn(CH3COO)2 in 20ml
of ethanolic solution. The solution was left to stand and a whitish precipitate separated
from the solution as the solution cooled. The precipitate was filtered in a sintered funnel
under suction and washed with water. The whitish product was air dried and stored in a
desiccator.
The method described above was used for the synthesis of 1-phenyl-3-methyl-4-Butyryl-
5-pyrazolonato Zinc (II) complex using 0.549g of Zinc Acetate and 1.221g of HPMBUP,
1-phenyl-3-methyl 4-Benzoyl-5-pyrazolonato Zinc (II) complex using 0.274g of Zinc
acetate (Zn(CH3COO)2) and 0.696g of HPMBP, 1-phenyl-3-methyl-4-propionyl-5-
pyrazolonato Zinc II complex (Zn(PMPRP)2 using 1.097g of Zn(CH3COO)2 and 2.303g
of HPMPRP, 1-phenyl-3-methyl-4-capyroyl-5-pyrazolonato Zinc (II) complex
Zn(PMCP)2 using 0.274g of Zn(CH3COO)2 and 2.723g of HPMCP and 1-phenyl-3-
methyl-4-palmitoyl-5-pyrazolonato Zinc (II) complex Zn(PMPP)2 .2H2O using 0.549g of
Zn(CH3COO)2 and 2.063g of HPMPP.
3.44 Preparation of 3M Hydrochloric acid solution
Fresh solutions of Hydrochloric acid used were prepared fortnightly. 3M
Hydrochloric acid solution was prepared by diluting 248.2cm3 of 37% HCl (sp.1.18) to
1000cm3 in a 1 litre volumetric flask with distilled deionized water. The volume of stock
acid diluted was obtained from the calculations below.
% purity of HCl=37%
Molecular weight of HCl=36.46gmol-1
55
Specific gravity= 1.18
Molarity of HCl= S.g x % purity x 1000
Molar mass or M W
= 1.19 X 0.37 X 100
36.46
Molarity of Conc HCl=12.08 mol dm-3
To prepare 1000cm3 of 3m HCl we used
C1V1=C2V2
C1=12.08moldm-3
C2=3moldm-3
V1=?
V2 = 1000cm3
V1 = (3 X 1000) Moldm-3
cm3
12.08 moldm-3
=248.2cm3
56
Fig 9.0: Reaction scheme for synthesis of a typical 4-acyl pyrazolone ligand and its
metal complex
N O
CH3
N
HPM P
ph
+
Ca(O H)2
N O
CH3
N
ph
O
Ca -H
N O
CH3
N
Calcium Com plex
C
H
Keto Form
N O
CH3
N
ph
C O H
enol form
N
CH3
N
ph
C O
O
M X H2O
M etal -4-Acyl pyrazolone
3M HCl
Reaction Schem e
O
ph
Ligand
R
R
R
Ligand
M (CH3CO O )
2.2H
2O
R-CoCl
R
57
3.50: PHYSICAL AND SPECTROSCOPIC STUDIES.
3.51: Melting point Determination. The melting points and dissociation temperatures
were determined using an electro thermal melting point apparatus with fine control.
3.52: Conductance Measurement
The molar conductance of each complex in DMF (Conc 10-3
M) measurements was
determined at 270C with the Jenway digital conductivity meter(model no J4500) using an
immersion type cell with a cell constant of 0.75.
3.53: Electronic Spectra Measurements
The electronic spectra of the ligands and complexes were obtained with a Jenway 6405
UV-visible spectrophometer coupled to a mecury computer monitor, in the department of
Pure and Industrial Chemistry ,University of Nigeria Nsukka
3.54: Infrared Spectra Measurement
The infrared spectra of the ligands and their Mg(II) Co(II), Cu(II) and Zn(II) complexes
were measured in the region of 4000-400cm-1
using the Perkin-Elmer fourier transform
infrared spectrometer ( model 2000) in the analytical and spectroscopic laboratory of the
department of chemistry, University of Waikato Newzealand.
58
CHAPTER FOUR
4.0 RESULTS AND DISCUSSION
4.10 Structure of ligands and complexes
Some 1-phenyl-3-methyl-4-acyl pyrazolone- 5 have been synthesized and the IR spectral
measurements (HPMAP,HPMBP,HPMBUP,HPMCP,HPMPRP,HPMPP,) showed that the
ligands may exist in four tautomeric forms as shown in figure 10.
CH3 C O
R
O
N
C6H
5
N
CH3 C O
R
O
N
C6H
5
N
O
C
RH
N
C6H
5
H
CH3
O
C
R
N
C6H
5
CH3
NH
O H
O
N
(a) (b)
(d)
Keto form s
Enol form s
(c)
Fig 10:Tautomeric forms of the ligand
R= HPMAP(1-phenyl-3-methyl-4-acetyl pyrazolone- 5), HPMBP(1-phenyl -3-methyl-4-
benzoyl pyrazolone-5) ,HPMBUP(1-phenyl-3-methyl-4-butyryl pyrazolone- 5), HPMCP(1-
phenyl-3-methyl-4-caproyl pyrazolone- 5),HPMPRP(1-phenyl-3-methyl-4-propionyl
pyrazolone- 5), HPMPP(1-phenyl-3-methyl-4-butyryl pyrazolone- 5).The results from
59
infrared spectral analysis showed that only three forms of the ligand were isolated from
aqueous ethanol and they are the forms in figures 10a, 10c and 10d above .The two enolic
tautomeric forms in 10c and 10d have been reported to be in resonace24
while the possibility
of an amino-diketo form of the ligand (10b) has been eliminated by the absence of bands
between 3100cm-1
-3500cm-1
in the anhydrous form of the ligand.
These tautomeric forms of the ligand have been found to behave as bidentate enols forming
neutral chelates of the type shown in figure 11 with Mg(II). Co(II), Cu(II) and Zn(II)
CH3
N
ph
OC
N O
M
ph
NO
O CH3
N
C
M = M g(II) or Co(II)
or Cu(II) or Zn(II) Ions.
R
R
Fig 11: Structure of metal complex.
60
4.20 Physical Data
Table 1 shows the physical data for the ligands while table 2 shows the physical data
for the Mg(II) Co(II) Cu(II) and Zn(II) complexes of the 4-acyl pyrazolones.
Table 1.0: Physical Data for the 4-acyl Pyrazolones
Molecular
formula
Molar
Mass
Colour Yield % Melting
Point 0C
C12H12N2
(HPMAP)
216.23
White
52
57-58
C17H1402
N2
(HPMBP)
278.32
White
85
115-117
C14H16O2N2
(HPMBUP)
244.29
Yellowish
brown
89
76-77
C16H20O2N2
(HPMCP)
272.35
Yellow
88
56-57
C13H14O2N2
(HPMPRP)
230.27
Yellow
75
61-62
C26H40O2N2
(HPMPP)
412.55 Bone
white
95 64-65
61
Table 2.0: Some Physical Data for Mg (11), Co (11), and Cu(11) and Zn(11) complexes
of some 1-phenyl-3-methyl 4-acyl pyrazolone-5.
Molecular Formular Molar Mass Colour Yield% M.P 0C
Mg C24H28O6N4
[Mg(PMAP)2.2H2O]
492.77 White 78.20 201-202
MgC34H32O6N4
[Mg(PMBUP)2.2H2O]
616.95 White 60.31 158-160
MgC28H36O6N4
[Mg(PMBP)2.2H2O]
548.89 Bone white 75.20 176-178
MgC32H44O6N4
[Mg(PMCP)2.2H2O]
605.85 Yellow 70.10 160-162
MgC26H32O6N4
[Mg(PMPRP)2.2H2O]
520.85 Yellow 55.09 182-183
MgC52H84O6N4
[Mg(PMPP)2.2H2O]
885.41 White 51.13 110-112
CoC24H28O6N4
[Co(PMAP)2.2H2O]
527.39 Pink 58.50 165-166
CoC34H32O6N4
[Co(PMBP)2 2H2O]
651.57
Pink
62.19
184-185
CoC28H36O6N4
[Co(PMBUP)2.2H2O]
583.47
Pink
50.01
145-147
CoC32H44O6N4
[Co(PMCP)2.2H2O]
639.63
Pink
72.69
137-328
CoC26H32O6N4
[Co(PMPRP)2.2H2O]
555.47
Deep pink
75.01
158-159
CoC52H84O6N4
[Co(PMPP)2.2H2O]
920.03
Pink
58.09
200-202
CuC24H28O6N4
[Cu(PMAP)2.2H2O]
532.00
Green
72.01
256-257
62
Molecular Formula Molar Mass Colour Yield % Melting point 0C
ZnC34H32O6N4
[Zn(PMBP)2.2H2O]
622.01
White
71.20
187-188
ZnC34H28O4N4
[Zn(PMBUP)2.]
553.95
Bone
White
62.10
144-145
ZnC32H44O6N4
Zn(PMCP)2
646.07
Yellowish
84.10
198-200
ZnC26H28O4N4
Zn(PMPRP)2
561.91
Yellow
58.13
169-170
ZnC52H80O4N4
[Zn(PMPP)2
890.47
Bone white
82.12
118-120
Molecular Fomular Molar Mass Colour Yield% M.P0C
CuC34H32O6N4
[Cu(PMBP)2.2H2O]
656.18
Green
60.56
269-270
CuC28H36O6N4
[Cu(PMBUP)2.2H2O]
588.12
Deep green
73.15
244-246
CuC32H44O6N4
[Cu(PMCP)2.2H2O]
644.24
Green
78.01
286-288
CuC26H32O6N4
[Cu(PMPRP)2.2H2O]
568.08
Green
67.12
294-296
CuC52H84O6N4
[Cu(PMPPP)2.2H2O]
924.64
Dirty green
70.09
244-250
ZnC24H28O6N4
[Zn(PMAP)2.2H2O]
533.83
White
86%
190-191
63
4.30: Conductivity Data
The molar conductance of 0.0001m solutions of the cobalt(II)copper(II) zinc(II) and 0.001m
magnesium(II)chelates in DMF at 27
0C are shown in tables 3a-d.The figures show that the
conductance values of all the complexes are negligible showing that all the cobalt(II),
copper(II) zinc and magnesium(II) complexes are neutral and non ionic.
Table 3a-3d: Conductivity Data for Mg (II), Co (II) Cu(II)and Zn complexes of 4-acyl pyrazolones.
Table 3a: Magnesium complexes
Complex Conc (mg/l) Molar Conductance (µohm-1m-1)
Mg (PMAP)2. 2H2O 0.012 8.6
Mg (PMPB)2. 2H2O 0.015 9.2
Mg (PMBUP)2. 2H2O 0.013 7.1
Mg (PMCP)2. 2H2O 0.012 8.3
Mg (PMPRP)2. 2H2O 0.01 3.8
Mg (PMPP)2. 2H2O 0.018 4.9
Table 3b Cobalt Complexes
Co (PMAP)2. 2H2O 0.01 4.8
Co (PMBP)2. 2H2O 0.013 6.9
Co (PMBUP)2. 2H2O 0.012 7.2
Co (PMCP)2. 2H2O 0.013 13.5
Co (PMPRP)2. 2H2O 0.011 2.7
Co (PMPP)2. 2H2O 0.018 15.1
Table 3c Copper Complexes
Cu (PMAP)2. 2H2O O.O1 21.5
Cu (PMBP)2. 2H2O 0.013 9.2
Cu (PMBUP)2. 2H2O 0.17 7.6
Cu (PMCP)2. 2H2O 0.007 23.6
Cu (PMPRP)2. 2H2O 0.028 12.9
Cu (PMPP)2. 2H2O 0.023 8.2
Table 3d: Zinc Complexes
Complex Conc (mg/l) Molar Conductivity ( µohm-1m-1)
Zn (PMAP)2. 2H2O 0.026 6.7
Zn (PMBP)2. 2H2O 0.012 1.6
Zn (PMBUP)2. 0.018 2.5
Zn (PMCP)2. 0.032 11.8
Zn (PMPRP)2. 0.028 0.72
Zn (PMPP)2. 0.022 2.5
64
4.40 Solubility Survey of Ligands and Complexes.
Tables 4a-4e show the solubility measurements for the ligands and their complexes in
various solvents. It was shown from table 4a that none of the ligand was soluble in water.
They were however soluble in most organic solvents.
Tables 4b-4e show that none of the metal complexes is soluble in water but have
varying solubility in various organic solvents. The magnesium (II) complexes show
solubility in most of the organic solvents, the cobalt (II) complexes also show varying degree
of solubility in the organic solvents, except the acetyl and palmitoyl complexes which were
insoluble in Diethyl ether and Acetone respectively. Also the Cu(II) and Zn (II) complexes
showed solubilities in most of the organic solvents with a few exceptions down the line.
Generally, it was observed that the complexes were hydrophobic. This reveals that the
distribution of these complexes from aqueous media into organic solvents such as
chloroform, Diethyl ether and CCl4, in which they are slightly soluble is favorable. The
complexes all showed remarkable solubility in DMF and DMSO, These two solvents have
lone pairs of electrons for donation, which probably completed the octahedron in the
complexes, thereby reducing further the ionic character of the complexes if any. These results
suggest that these two solvents could be efficient synergists in the extraction of Mg(II) Co(II)
Cu(II) and Zn(II) ions from aqueous media123
.
Table 4a solubility Data for the ligands
Solvent HPMAP HPMBP HPMBUP HPMCP HPMPRP HPMPP
Water i i I I i i
Ethanol S S S S S S
Methanol S S S S S S
Acetone VS VS VS VS VS VS
Dioxane VS VS VS VS VS VS
D. ether VS VS VS VS VS VS
T.H.F VS VS VS VS VS VS
CCL4 VS VS VS VS VS VS
n-hexane VS VS VS VS VS VS
Pyridine VS VS VS VS VS VS
Benzene VS VS VS VS VS VS
DMF VS VS VS VS VS VS
DMSO VS VS VS VS VS VS
65
Table 4b: solubility data for Magnesium (ii) complexes of the ligands
Solvent Mg
(PMAP)2.
.2H20
Mg
(PMBP)2
.2H20
Mg
(PMBUP)2
.2H20
Mg
(PMCP)2
.2H20
Mg
(PMPRP)2
.2H20
Mg (PMPP)2
.2H20
Water i i I I i I
Ethanol S S SP SP S S
Methanol SP SP SP I i I
Acetone VS VS S S SP SP
Dioxane VS S S S S SP
D. ether S S SP S S S
T.H.F VS VS S VS SP S
CCL4 S S SP S S S
n-hexane S SP I VS i i
Pyridine VS VS S S VS VS
Benzene SP SP I S SP SP
DMF VS VS VS VS VS VS
DMSO VS VS VS VS VS VS
Table 4c: solubility data for Cobalt (ii) complexes of the ligands
Solvent Co (PMAP)2
.2H20
Co (PMBP)2
.2H20
Co
(PMBUP)2
.2H20
Co (PMCP)2
.2H20
Co
(PMPRP)2
.2H20
Co (PMPP)2
.2H20
Water i i I I i i
Ethanol SP SP I I i i
Methanol SP SP I I SP i
Acetone SP SP SP I SP SP
Dioxane SP S S S S S
D. ether i VS SP S SP VS
T.H.F VS VS VS VS SP VS
CCL4 SP VS SP SP SP S
n-hexane i S SP SP S SP
Pyridine VS VS VS S VS VS
Benzene i S SP SP SP SP
DMF VS VS S VS VS VS
DMSO VS S S VS VS VS
Table 4d:solubility data for Copper(ii) complexes of the ligands
Solvent Cu (PMAP)2
.2H20
Cu (PMBP)2
.2H20
Cu
(PMBUP)2
.2H20
Cu (PMCP)2
.2H20
Cu
(PMPRP)2
.2H20
Cu (PMPP)2
.2H20
Water i i I I i i
Ethanol SP SP I I S i
Methanol SP SP I I S i
Acetone SP SP I SP VS i
Dioxane SP S SP SP SP SP
D. ether i SP SP SP VS SP
T.H.F S S S S VS S
CCL4 SP S SP S VS SP
n-hexane SP S SP SP SP i
Pyridine VS VS S SP VS S
Benzene i S I SP S i
DMF VS S VS VS VS VS
DMSO VS S VS VS VS VS
66
Table 4e:solubility data for Zinc(ii) complexes of the ligands
Solvent Zn (PMAP)2
.2H20
Zn (PMBP)2
.2H20
Zn
(PMBUP)2
Zn (PMCP)2
Zn
(PMPRP)2
Zn (PMPP)2
Water i i I I i i
Ethanol i i I SP i i
Methanol i i I SP i i
Acetone SP VS SP S SP i
Dioxane SP VS S S SP SP
D. ether i S S VS i SP
T.H.F i VS S VS VS S
CCL4 SP S SP VS SP SP
n-hexane SP SP SP SP SP SP
Pyridine SP VS VS VS VS S
Benzene SP S SP SP SP i
DMF SP VS VS VS VS S
DMSO SP VS VS VS SP S
Legend:i=insoluble,S=soluble,SP=sparingly soluble,VS=very soluble
4.50 Electronic spectra of ligands and complexes
Table 5a and 5b show the UV-visible spectral data for the ligands and their
magnesium(II), cobalt(II), copper(II) and Zn (II) complexes. Without the required quantum
mechanical calculations, assignment of the absorption bands to definite electronic transition
with complete certainty may not be possible, it is reasonable however to assign the bands
1 and
2 of the ligand anions to -*
transitions. From table 5b, it is evident that some of
the ligands suffered slight bathochromic shift in the 1
and 2
bands on chelation with the
metals and this agrees with previous observation. 64,79,157
Some hypsochromic shifts were
observed for the 1
and 2
bands of some other metal complexes of the ligand. This
observation is an exception to the general rule that there is always a bathochromic shift on
chelation to a metal atom shown by most 1,3 diketonates.64
Okafor 159
reported a similar
observation for rare earth trischelate of 4-acyl-pyrazolone. The 1
and 2
absorption bands
for the complexes are also due to intra ligand -*transitions. However the molar extinction
measured at identical wave lengths shows significant differences. It is pertinent to state that
the UV spectra of the complexes are similar in character to those of the free ligands,
indicating that the -bonding system in the free ligand is almost intact in the metal complex.
Thus only the orbital of the oxygen atom is substantially involved in -bonding with the
67
central metal. 20, 64, 123
The third absorption band 3
which appeared in the complexes of
cobalt (II), copper (II) and some of the Zinc(II) complexes of the ligands has been ascribed
to metal to ligand charge transfer. The molar absorptivity E which are mostly of the order of
103 supports this assertion
Table 5a: Electronic spectral Data of the Ligands
Ligand 1
max
(nm) E1(mol-1
cm-1
) 2
max
(nm) E2 (mol-1
cm-1
)
HPMAP 329.4 1.0 x104 359.4 5.9 X 10
4
HPMBP 321.8 3.0 x 103 354.2 5.4 x 10
4
HPMBUP 328.2 7.4 x 103 360.0 5.5 x 10
4
HPMCP 322.6 5.7 x 103 334.2 4.7 x 10
4
HPMPRP 327.4 9.6 x 103 360 5.8 x 10
3
HPMPP 321.8 4.6 x103 326 2.7 x 10
4
Table 5b: Electronic spectral Data of Mg(II) Co(II) Cu(II) and Zn(II) complexes of some 4-acyl pyrazol-5-
ones.
Complexes 1
Max (nm) E1(mol-1cm-1)
2 Max (nm)
E2(mol-1cm-1) 3
Max
(nm)
E3(mol-1cm-1)
Mg (PMAP)2. 2H2O 320.52 4.2 x 103 347.10 1.0 x 10
4
Mg (PMBP)2. 2H2O 331.60 9.6 x 103 334.50 2.4 x 10
3
Mg (PMBUP)2. 2H2O 329.2 6.2 x 103 355.00 3.8 x 10
4
Mg (PMCP)2. 2H2O 3276.6 5.1 x 103 363.60 1.7 x 10
4
Mg (PMPRP)2. 2H2O 328.5 3.6 x 103 365.12 3.0 x 10
4
Mg (PMPP)2. 2H2O 303.6 4.9 x 103 341.20 9.2 x 10
4
Co(PMAP)2. 2H2O 317.6 1.4 x 103 394.2 1.0 x 10
4 426 4.0 x 10
3
Co(PMBP)2. 2H2O 303. 6 1.1 x 104 356.8 2.1 x 10
3 476 8.5 x 10
3
Co(PMBUP)2. 2H2O 296 5.6 x 103 361.2 2.6 x 10
4 484.6 6.5 x 10
3
Co(PMCP)2. 2H2O 298 6.9 x 104 368 1.7 x 10
3 446 2.5 x 10
3
Co(PMPRP)2. 2H2O 314 1.43 x 104 343.6 3.6 x 10
4 497.8 2.1 x 10
3
Co(PMPP)2. 2H2O 293.4 3.2 x 103 364.2 9.0 x 10
3 502.4 3.0 x 10
3
Cu (PMAP)2. 2H2O 307.2 9.2 x 103 371.20 2.6 x 10
3 488.1 4.1 x 10
4
Cu (PMBP)2. 2H2O 298.2 8.4 x 103 362.10 1.6x 10
3 493.2 1.7 x 10
3
Cu (PMBUP)2. 2H2O 314.2 6.7 x 103 372.2 4.6 x 10
4 498.6 9.6 x 10
3
Cu (PMCP)2. 2H2O 293.2 2.8 x 103 360 3.0 x 10
4 495.2 1.0 x 10
4
Cu (PMPPP)2. 2H2O 308.2 4.2 x 103 353.2 3.2 x 10
4 499.4 1.0 x 10
3
Cu (PMPP)2. 2H2O 312.1 1.9 x 103 358.1 4.2 x 10
4 472 3.6 x 10
3
Zn (PMAP)2. 2H2O 322.6 3.7 x 103 326.2 3.2 x 10
4
Zn (PMBP)2. 2H2O 338.0 4.6 x 103 355.2 4.3 x 10
4
Zn (PMBUP)2. 322 3.1 x 103 332.2 5.6 x 10
4
Zn (PMCP)2. 322 4.2 x 104 372 3.5 x 10
4 497 4.5 x 10
3
Zn (PMPRP)2 321 4.3 x 103 376.2 2.6 x 10
3 493.2 3.0 x 10
3
Zn (PMPP)2 322 2.7 x 103 360 7.0 x 10
3 492 3.5 x 10
3
68
4.60 Infrared spectra of ligand and complexes
Reference was made to IR spectra of previous work done on 4-acylpyrazol -5-ones, 13,14,16-
20,25,37 In the assignment of the vibrational frequencies of the ligands and their Mg(II), Co (II)
Cu(II) and Zn(II) complexes. The IR spectral data (4000-400)cm-1
of the ligands and their
metal chelates with the possible assignment are given in tables 6a – 6f.
Table 6a: Infrared Frequencies of 1-phenyl-3-methyl -4-acetyl pyrazolone-5- one and
its Mg (ii), Cu(ii),Co(ii) and Zn(ii complexes.
HPMAP Co (PMAP)2 Cu (PMAP)2 Mg (PMAP)2 Zn (PMAP)2 Assignments
3468br 3573 sh 3468 br
3415 br 3574 sh v-O-HO-H2O
3341 br 3349br
3067 w 2985 w 3065 m 3065 w 2985 w Aryl –C-H
2991 w 2966 w 2965 w 3002 w 2957 w Saturated – C-H
2923 m 2920 m 2922 s 2926 w 2921 m vC-H
1639 vs - - - - v C=O
1623 vs 1606 s 1644 s 1623 vs vas C=O
1592 s 1594 vs 1592 s 1599 vs 1594 vs Phenyl ring VC=C
- 1582 m 1577 vs 1557 m 1588 s Pyrazole ring stretch
1535 s 1540 s - 1535 sh Pyrazole ring stretch
1500 m 1485 vs 1497 s 1512 br 1488 s vas C=C=C
1460 m - 1463 w 1472 w - Phenyl ring stretch
1440 m - 1442 m 1443 w - βas CH3
1399 sh 1404 w 1410 m 1416 w 1403 m Pyrazole ring stretch
1363 w 1375 vs 1380 s 1366 s 1375 vs vs C=O
1342 w - 1351 w 1343 w - βs CH3
1214 s 1214 m 1229 s 1214 w 1214 m vs C=C=C
1100 w 1156 w 1176 w 1184 w 1157 w βC-H
1161 s 1133 w - 1155 s 1133 w βC-H
1085 vs 1080 vs 1087 vs 1087 vs 1080 vs C-H In plane Deformation
1052 w 1055 w 1055 w - 1055 m C-H In plane
1027 s 1031 m 1031 s 1027 vs 1031 s Mono sub. Phenyl ring
1011 w 1014 m 1017 w 1019 s 1014 w CH3-rock out of plane
1001 w 998 w 999w 1001 w CH3-rock In plane
969 s 969 vs 974 vs 963 vs 968 vs C-C6H5 – stretch
909 s 914 s 907 s 906 s 914 s CH3 Stretch
834 m 844 s 848 s 848 s 844 -CH
750 vs 759 w 756 vs 761 vs 759 vs -CH
728 s 695 vs 749 m 749 sh Phenyl ringDeformation
690 vs 659 m 690 vs 691 m 696 vs Chelate ring Deformation
653 m 609 s 659 s 664 w 650 m Chelate ringDeformation
580 m 609 s 611 s 609 vs 608 vs Chelate ring vibration
507 s 510 s 513 s 510 m 509 vs Chelate ringVibration
- 448 s 477 m 493 s 447 m vM-O
- 404 w 414 m 424 w 404m Chelate ring Vibration
Legend = br=Broad, vs = very strong, S = strong, Sh sharp, W=weak Vw = very weak v=Sretching
frequency,β=bending or defomation,νas=Asymetric stretching,νs = Symetric stretching, =out of plane
bending
69
Table 6b:Infrared Frequencies of 1-phenyl-3-methyl 4-Benzoylpyrazol- 5-one and its
Co(ii), Cu(ii), Mg(ii) and Zn(ii) complexes HPMBP Co (PMBP)2 Cu (PMBP)2 Mg (PMBP)2 Zn (PMBP)2 Assignments
3467 br 3401 br 3448 br 3361 br 3342 br v-O-H-O H2O
3058 sh Aryl C-H
2924 sh 2926 sh - Saturated C-H
2852 sh - v-CH
2581 br - - - - v-O-H
1646 s - - - - vC=O enol
1604 s 1603 s 1626 s 1698 vs vas C=O
1597 w 1559 m 1592 w 1595 w 1528 sh Phenyl ring vC=C
1579 w - 1563 s - - Pyrazole rings stretch
1497 w 1499 s 1499 sh 1501 s 1482 w vC=C=C
1458
sh
1457 sh 1459 sh 1459 w - Phenyl ring stretch
- - 1441 s 1435 s 1433 s βas CH3
1400 s 1414 m 1423 w 1399 w 1399 s Pyrazole ring stretch
1348 s 1378 m 1380 vs 1359 s 1377w vs C=O
1310 m 1353 m 1354 m 1314 w - βs CH3
1221 m 1285 s 1245 w 1232 m 1244 vs vs C=C=C
1196 s 1192 m 1176 w 1177 w 1178 w β C-H
1182 w 1145 s 1162 s 1155 s 1159 s β C-H
1182 w 1110 m 1124 m 1133 s 1127 m Pyrazole ring breathing
1107
vs
1070 w 1072 m 1074 m 1074 w C-H Inplane deformation
1074 s 1021 m 1021 s 1026 sh 1020 s C-H In plane Mono sub
ph ring
992 m 1008 w 1001 w 1000 sh 1000 sh CH3 rocking
949 s 948 s 954 vs 949 vs 950 vs C-C6H5 stretch
932 vs 938 sh 934 w 919 w 926 w C-CH3 stretch
832 vs 831 s 843 s 841 vs 846 vs -CH
798 s 799 m 797 m 795 m 799 w -CH
706s 730 w 704 s 703 vs 701 s C-H out of plane
deformation of phenyl
ring
687 s 690 s 689 s 671 w 672 sh Chelate ring deformation
610 vs 601 s 613 sh 613 s 613 vs Chelate ring Vibration
534 s 539 s 567 s 552 m 552 s Chelate ring Vibration
493 s 504 s 518 s 508 s 508 vs Chelate ring Vibration
- 447 s 464 s 454 s 459 s v M-O
Legend = br=Broad, vs = very strong, S = strong, Sh sharp, W=weak Vw = very
weak v=Sretching frequency,β=bending or defomation,νas=Asymetric
stretching,νas = Symetric stretching, =out of plane bending
70
Table 6c: Infrared Frequencies Of 1-Phenyl-3-Methyl 4-ButyrylPyrazol-5-one and its
Co(ii), Cu(ii), Mg(ii) & Zn(ii) Complexes
HPMBUP Co (PMBUP)2 Cu
(PMBUP)2
Mg (PMBUP)2 ZN (PMBUP)2 Assignments
3470 br 3401 br 3468 br 3430 br - v-O-OH water
3065 w 3060 w 3062 w 3063 w 3060 w Aryl-C-H
2996 w 2957 s 2957 w 2957 s 2955 w Saturated C-H
2933 w 2931 w 2928 w 2932 s 2928 v-C-H
1617 s - - - - v C=O
1626 vs 1609 s 1643 vs 1615 s vas C=O
1597 sh 1592 w 1599 sh 1580 w Phenyl ring C=C
1562 s 1580 w 1577 vs 1582 vs 1534 s Pyrazole ring stretch
1499 sh 1509 vs 1500 vs 1512 s 1508 s vC=C=C
1461 s 1461 w 1462 w 1462 w 1462 w Phenyl ring stretch
1427 sh 1439 w 1442 s 1440 s 1439 s βas CH3
1392 s 1395 s 1383 vs 1396 s 1397 m vs C=O
1315 m 1324 m 1330 w 1324 s 1328 w βs CH3
1267 s 1265 w 1276 w 1274 w 1276 n vs C=C=C
1197 s 1195 m 1177 w 1196 w 1180 w β C-H
1154 w 1148 w 1157 m 1183 w 1180 w β C-H
1120 w 1105 w 1101 w 1107 w 1106 s C-H deformation in
plane
1097 m 1079 s 1078 vs 1080 vs 1079 vs C-H deformation in
plane
1077 w 1069 w 1062 s 1070 s - C-H Inplane deformation
of mono substituted ring
1063 w 1033 s 1035 s 1034 s 1032 s C-H Inplane deformation
of mono substituted ring
1032 s 1022 w 1020 w 1020 w 1022 w C-H deformationof mono
substituted ring
1001 s 1002 1003 s 1002 s 1003 s CH3 rocking
990 s - 990 s 993 s CH3 rocking
906 m 903 s 907 s 903 vs 904 vs C-C6H5 stretch
876 m 877 m 879 w 878 s 877 m C-CH3 stretch
783 s 804 w 808 s 807 m 205 w -C-H
756 vs 754 vs 760 vs 764 s 754 vs -C-H
691 vs 690 vs 690 vs 690 m 680vs Chelate ring deformation
684 w 665 m 659 s - 643 m Chelate ring deformation
642 m 644 w 640 sh 624 s 621 s Chelate ring deformation
607 m 616 s 614 sh - - Chelate ring vibration
500 s 508 s 510 s 506 vs 510 vs Chelate ring vibration
- 455 vs 489 vs 470 vs 467 vs vM –O
- 422 m 426 m 414 m vM–O
Legend = br=Broad, Vs = very strong, S = strong, Sh sharp, W=weak Vw = very weak
V=Sretching frequency,β=bending or defomation,νas=Asymetric stretching,νs = Symetric
stretching, =out of plane bending
71
Table 6d: Infrared frequencies of 1-phenyl-3-meltal 4-capyroylpyrazol-5-one and its
Co(ii), Cu(ii), Mg(ii) and Zn(ii) complexes
HPMCP Co (PMCP)2 Cu (PMCP)2 Mg (PMCP)2 Zn (PMCP)2 Assignments
3467 br 3392 br 3336 br 3428 br 3190 br v-O-HO-Water
- 3092 br 3058 m 3057 w 3054 w Aryl-C-H
2953 m 3056 w 2955 s 2954 s 2956 m Saturated C-H
2926 w 2953 s 2925 w 2939 m 2927 m v-C-H
1634 vs - - - - vC=O
- 1641 vs 1624 vs 1649 vs 1613 s vas C=O
1595 w 1595 m 1592 m 1598 s 1594 s Phenyl ring C=C
1562 s 1578 s 1577 s 1579 w 1578 w Pyrazole ring
stretch
1561 vs 1506 vs 1499 vs 1511 vs 1507 vs vC=C=C
1460 m 1456 m 1464 w 1476 w 1476 w Phenyl ring stretch
1443 w 1439 w 1441 s 1440 m 1441 s βas CH3
1363 w 1362 s 1377 vs 1363 vs 1370 vs vs C=O
1330 w 1324 s 1327 s 1324 s 1325 s βs CH3
1228 vs 1225 vs 1207 w 1225 m 1225 w vs C=C=C
1187 m 1187 w 1154 w 1192 w 1199 w β-C-H
1158 s 1154 s 1101 w 1154 m 1154 w β-C-H
1099 m 1078 vs 1079 vs 1080 vs 1079 vs C-H.inplane
deformation
1076 vs 1065 w 1064 s 1066 s 1066 s C-H.inplane
deformation
1031 s 1032 w 1032 s 1033 s 1033 s Mono subst ring def
1005 s 1012 s 1015 w 1013 s 1015 s CH3 rocking
- 998 s 999 s 999 s 998 s CH3 rocking
909 vs 903 vs 905 vs 902 s 904 s C-C6H5 stretch
855 m 846 s 849 vs 847 vs 850 vs C-CH3 stretch
827 w 800 w 805 s 802 m 801 w -CH
778 vs 767 s 768 w 789 m 768 w -CH
775 vs 755 vs 756 vs 755 vs 756 vs -CH
691 vs 689 vs 690 vs 689 vs 688 w Chelate
634 vs 663 w 662 s 662 s 668 w Ring
622 s 627 vs 623 s 621 vs Deformation
607 s 614 s 614 w 615 w - Chelate ring
507 vs 509 vs 511 sh 507 vs 511 vs Vibration
- 457 vs 495s 469 s 469vs vM-O
453 - 445 426 416 Chelate ring
vibration Legend = br=Broad, Vs = very strong, S = strong, Sh sharp, W=weak Vw = very weak
V=Sretching frequency,β=bending or defomation,νas=Asymetric stretching,νs = Symetric
stretching, =out of plane bending
72
Table 6e: Infrared Frequencies of 1-Phenyl-3- methyl -4-PropionylPyrazol-5-one and
its Co(11), Cu(11), Mg(11) and Zn(11) Complexes
HPMPRP CO (PMPRP)2 Cu (PMPRP) 2 Mg (PMPRP) 2 Zn (PMPRP) 2 Assignments.
3469br 3421 br 3468 br 3429 br – vO –HO
water
- 3061 W 3065Sh 3065w 3062Sh Aryl.C-H
2973M 2991W 2985m 2990Sh 2983W Saturated C-
H
2934W 2934M 2941Sh 2934S 2935Sh vC-H
1626S - - - - vC=O
1624Vs 1607Vs 1639Vs 1619Vs vas C=O
1572M 1597S 1574S 1599S 1595W Phenyl ring
vC=C
1527W 1544W 1538VS 1560W 1531W Pyrazole ring
stretch
1504Sh 1509VS 1497S 1513Vs 1509S vasC=C=C
1493W 1471W 1475Sh 1476S Phenyl ring
stretch
1444M 1440W 1440S 1441S 1442S βas CH3
1374W 1371W 1380S 1362S 1367S vs C=O
1332Sh 1325W 1328M 1325M 1327W βsCH3
1210M 1267W 1219M 1224W 1206W vs C=C=C
1183M 1196W 1180W 1196W 1183W βC-H
1160W 1147M 1127M 1148M 1045M βC-H
1084Vs 1079Vs 1079Vs 1081VS 1079Vs C-H inplane
Mono
Subititued
Phenyl Ring
1060W 1067W 1060W 1068W 1067Vs
1034M 1033S 1034S 1034S 1033S
1003S 1006Vs 1006Vs 1006Vs 1007 CH3 Rocking
963S 959S 962S 959Vs 960S C-C 6H5
Stretch
73
HPMPRP Co(PMPRP)2 Cu(PMPRP)2 Mg(PMPRP)2 Zn(PMPRP)2 Assignments
758S 816S 812VS 818Vs 815Vs -CH
740W 752VS 751VS 754VS 753Vs . -CH
689S 688S 690S 689Sh 688S Chelate ring
Deformation
639M 662M 659S 665W 658W Chelate ring
def
- 645W 641W 623W 642Sh Chelate ring
def
605M - - - - Chelate ring
vib
507S 507S 512M 503S 510Vs Chelate ring
vib
- 448S 497S 470S 459S v M-O
Legend = br=Broad, Vs = very strong, S = strong, Sh sharp, W=weak Vw = very weak
V=Sretching frequency,β=bending or defomation,νas=Asymetric stretching,νs= Symetric
stretching, =out of plane bending
74
Infrared vibrational frequencies of 1- Phenyl-3- methyl -4-Pamitoyl Pyrazolone and its Co(ii),
Cu(ii), Mg(ii) and Zn (ii)Complexes
HPMPP Co (PMPP)2 Cu (PMPP) 2 Mg (PMPP) 2 Zn (PMPP) 2 Assignments.
- 3401 br 3469 br 3433 br – vO –HO water
- - 3064 sh 3063 w Aryl C-H
2917s 2920w 2919 s 2921 s 2921s Saturated C-H
2849m 2853s 2851 s 2851 s 2850 s v-CH
2677Br - - - - v-OH-O
1627s - - - - vC = O
1646s 1626 m 1652 s 1614 s vas C =O
1594w 1595s 1591 s 1599 m 1596 sh Phenyl ring C=
C
1558m 1559s 1575 s 1580 w 1581 w Pyrazole ring
stretch
1500w 1501sh 1542 s 1513 s 1534 m vC= C=C
1472s 1473s 1563 m 146B m 1468 m Phenyl ring
stretch
1431m 1440 w 1441 m 1440 m 1441 w βas CH3
1348w 1394 m 1381 vs 1395 s 1371 vs vs C= O
1329w 1316 w 1327 w 1323 w 1328 w βs CH3
1228s 1217 m 1224 w 1217 w 1204 w Ѵ s C= C= C
1127s 1198 m 1198 m 1197 m 1145 w
β C-H
1122w 1178 w 1129 w 1170 w 1178w
1090s 1079 vs 1079 vs 1080 vs 1079 vs C-H In plane
Deformation 1079s 1067 w 1061 m 1068 m 1069 w
1063w 1034 m 1032 m 1034 s 1032 s C-H In Plane
def
1034w 1001 m 1001 s 1000 m 1001 s CH3 rocking
75
HPMPP Co(PMPP)2 Cu(PMPP)2 Mg(PMPP)2 Zn(PMPP)2 Assignments
1009w 905 w 985 s 980 vs 985 s CH3 rocking
940vs 912 m 905 m 912 m 908 m C-C6H5 Stretch
849w 847 w 846 m 847 m 847 m C-CH3 Stretch
782s 780 m 782 m 754 vs 752 vs
-CH 749m 749 s 752 vs 720 m -
688vs 689 s 689 vs 689 s 687 s Chelate ring
Deformation 640w 640 w 661 m 623 m 620 s
607s 607 w 532 w 532 w 509 s Chelate ring
vibration
547s 507 s 509 s 506 s 405 w
- 466 w 476 w 468 m 469 m vM-O
440m 416 m - - - Chelate ring
Vibration.
Legend = br=Broad, Vs = very strong, S = strong, Sh sharp, W=weak Vw = very weak
V=Sretching frequency,β=bending or defomation,νas=Asymetric stretching,νs Symetric
stretching, =out of plane bending.
The features of the IR spectra that are of most interest are outlined below.
(1) The presence of coordinated water in each of the Mg(II) Co(II) Cu(II) and some of the
Zn(II) chelates is indicated by the presence of broad peaks between 3100cm-1
and
3600cm-1
attributable to the OH stretching frequency of water.
(2) The intense bands centered at 2800cm-1
in the IR spectrum of some of the ligands
which has been attributed to asymmetric stretching frequencies of OH groups in enols
present in some of the ligands are absent in the spectra of all the metal complexes.
This indicates the participation of the OH in bonding.
76
(3) The shift of the νC=O stretching frequency of the ligands towards higher or lower
frequencies in their metal complexes, suggest that carbonyl groups are involved in
Chelation. The νC=O stretching frequencies of ligands and the asymmetric
frequencies of the metal chelates are shown in table 7.0.
(4) The absence of any peak between 3100cm-1
and 3600cm-1
in the anhydrous
complexes indicates the absence of ν-(NH-) and this eliminates the possibility of any
amino –diketo tautomeric form, reacting only through one or two of the carbonyl
groups or forming a coordinate link to the metal through the nitrogen atom of its
secondary amino group.
(5) The presence of bands between 400cm-1
and 500cm-1
typical of metal-oxygen
stretching frequencies of metal 1,3-diketonates suggests bonding through oxygen
atom 17, 25,37
. The exact vibrational frequencies assigned to the metal- oxygen bond
stretching frequencies are listed in table 7.0
The IR spectra of the ligands and their Mg(II), Co (II), Cu(II) and Zn (II) complexes
listed in tables 6a-6e above are divided into three main regions; 3600-1800cm-1
, 1800-
700cm-1
and 700-200cm-1
3600-1800cm-1
region
The most important feature of the chelate spectra of complexes in this region is the
presence of broad absorption bands in the IR spectra of the Mg(II), Co (II), Cu (II) and
some of the Zn (II) complexes which have been assigned to adduct water molecule
coordinated to the central metal ion or residing in the crystal lattice of the complexes.123
The absence of any peak between 3100cm-1
and 3600cm-1
in the anhydrous Zn (II)
complexes of the propionyl (Zn(PMPRP)2 Butyryl, (Zn(PMBUP)2) and palmitoyl
(Zn(PMPP)2 derivatives of the 4-acyl pyrazolone-5 clearly indicates the absence of
coordinated or crystal lattice water or solvent molecules. 28
. The presence of broad
absorption bands between 2000 and 2800cm-1
in the IR spectra of the Benzoyl (HPMBP)
77
and palmitoyl (HPMPP) derivatives of the 4-acyl pyrazol-5-ones which disappeared on
chelation has been ascribed to the presence of OH group of the enol form of the ligand
which was deprotonated on chelation with metal ion.
1800-700cm-1
region
This region contains bands derived from benzene, pyrazole and chelate ring
vibrations.These bands have been assigned by comparism with infrared spectral data
of the complexes of HPMBP 96
, HPMTFP 28,65
and HPMBUP 95
.The area of utmost
interest in this region are the C=O and C=C stretching frequencies (νas C=O and vas
C=C) of the chelate ring. These have been reported to be very sensitive to substitution
in -diketones 96
. The very intense bands located between 1600 and 1699cm-1
and
other strong bands observed between 1475cm-1
and 1540cm-1
in the spectra of the
chelates are attributed to νas C=O and vas C=C modes respectively. Table 7.0 shows
the observed νas C=O bands for all the metal chelates and it was observed that there is
a shift in the νC=O absorption bands to the νas C=O of the metal chelates.This
Suggests that the carbonyl group was involved in Chelation hence the formation of a
C=O-M bonding systems95
.Replacement of the methyl group of the acetyl moiety
with a phenyl group in the metal chelate shifts the C=O stretching bands to lower
frequencies. This suggests that there is a decrease in electron density around the C=O
bond, thus a decrease in the stability of the C=O bonding system.The stability order of
the νas C=O for the transition metals did not follow strictly the Irving Williams
stability order for transition metal complexes.(Cu > Ni > Co >Mn > Zn).
700-400cm-1
region
The metal-ligand vibrations below 700cm-1
are important because they
provide information on the strength of the M-O bonds and hence the stability of the
complexes. Metal isotopic substitution and normal coordinate analysis have shown
that pure M-O stretch (νas M-O) absorbs near 450cm-1
in acetylacetonates 96,159, 160
.
78
Table 7.0 shows the M-O stretching frequencies of some 1-phenyl-3-methyl-4-acyl
pyrazolone-5 and their metal chelates. The chelates were shown to have absorbed
between 439cm-1
and 497cm-1
indicative of M-O coordination. It was clearly shown
from the table that replacement of the methyl group of the acetyl moiety with a phenyl
group shifts the M-O stretching bands to lower frequencies. This is an indication that
the phenyl group substitution has caused a decrease in the electron density of the M-
O bond. Similar observation has been reported by Okafor96
. For the transition metal
chelates, the M-O stretching frequencies for all the 4-acyl substituents except the
Benzoyl followed the order Cu > Co > Zn, which conforms to the Irving Williams
stability order for transition metal complexes.
Table 7.0: Comparism of the vasC=O and vasM=O stretching frequencies of some
4-acyl pyrazolones and their divalent metal chelates.
vasC=O (cm-1
) vasM-O (cm-1
)
Compound Ligand Mg(II) Co(II)F Cu(II) Zn(II) Mg(II) Co(II) Cu(II) Zn(II)
HPMAP 1639 1644 1623 1606 1623 473 448 497 439
HPMPRP 1626 1639 1624 1607 1619 470 453 497 449
HPMBUP 1617 1643 1626 1609 1618 470 459 489 457
HPMCP 1634 1649 1634 1624 1613 469 471 485 469
HPMPP 1627 1652 1646 1626 1610 468 476 476 469
HPMBP 1646 1626 1604 1603 1698 454 447 464 459
79
4.70:The Effect of 4-acyl Substituents on the Infrared Carbonyl
Stretching Frequency of Metal (11) Chelates of some 1-Phenyl -3- Methyl
-4-acyl pyrazolones.
The infrared carbonyl stretching frequency of the metal(11) chelates are shown in table 7.0,
A close look at the data shows that for the 4-acetyl pyrazolone ligand, the order of stability
for transition metal chelates is as follows, Cu =Zn >Co which does not correspond to the
Irving Williams stability order for transition metal complexes.(Cu >Ni>Co>Mn>Zn). Similar
results were also observed for the transition metal chelates of HPMRP(Co >Zn >Cu),
HPMBUP(Co >Zn > Cu), HPMCP(Co > Cu > Zn), HPMPP (Co > Cu > Zn) and HPMBP
(Zn > Co > Cu) which does not equally follow the Irving Williams stability order for
transition metal complexes.28
In comparism with the infrared carbonyl stretching frequency, the metal-oxygen stretching
frequency of the transition metal chelates were also studied and the results shown in table 7.0
followed the trend HPMAP(Cu > Co >Zn), HPMPRP (Cu > Co > Zn), HPMBUP(Cu > Co >
Zn), HPMCP(Cu > Co > Zn), and HPMBP(Cu > Zn > Co). The above trend shows that the
infrared metal-oxygen stretching frequency for the transition metal chelates of all the 4-acyl
substituents except the Benzoyl derivatives followed closely the Irving Williams stability
order for transition metal complexes.28
Also looking at the data in table 7.0 down the
vertical axis, it will be noticed that there is a gradual change in the infrared carbonyl
stretching frequency of the metal chelates as the nature of the alkyl substituent at the 4-acyl
position changes, thus different correlation curves have been plotted for all metal chelates
showing the change in the infrared carbonyl stretching frequency as the molecular weight of
the substituent at the 4-acyl position increased.
Fig 12.0 shows the change in νC=O of the ligands as the molecular weight of the alkyl
substituent at the 4-acyl position increased. The curve shows that there is a noticeable change
in the infrared carbonyl stretching frequency with change in the alkyl substituent at the 4-
80
acyl position but in no particular order. Fig 13 shows some linearity with increase in the
length of the alkyl substituent at the 4-acyl position for the magnesium(11) chelates, with a
little deviation where the νasC=O for HPMPRP (1639cm-1
) is less than that for
HPMAP(1644cm-1
) which has a much lesser molecular weight. Figures 14 and 15 show the
plot of the νasC=O against the molecular weight of the alkyl substituents at the 4-acyl position
for the cobalt(11) and copper (11) chelates respectively. The two curves show that there is a
gradual increase in the νasC=O of the metal chelates as the length of the alkyl substituent at
the 4-acyl position increased, thus resulting in increased stability of the C=O bond .This
observation is as a result of increase in electron density around the C=O bond as the length
of alkyl substituent at the 4-acyl position increased.96
Plotted in figure 16 is νasC=O against
the molecular weight of the alkyl sustituents at the 4-acyl position for the Zinc chelates. The
curve shows that there was a gradual decrease in the value of the νasC=O as the molecular
weight of the alkyl substituent at the 4-acyl position increased, thus a decreased stability of
the C=O bonding system. The reason for this observation has not been completely established
but we ascribed it to be as a result of electronic and stearic interactions between the Zinc
metal ion and the pyrazole moiety.
81
82
The effect of the alkyl substituents at the 4-acyl position on the infrared metal-oxygen
stretching frequencies of the metal chelates was also studied using figures 17,18,19and 20
below. Figures 17 and 19 show the plots of the νasM-O against the molecular weight of the
alkyl substituents at the 4-acyl position for magnesium(11) and copper(11) chelates
respectively.
83
84
The nature of the two curves shows that there was a decrease in value of the νasM-O as the molecular
weight of the alkyl substituents at the 4-acyl position increased, thus a decrease in stability of the
metal-oxygen bond for both complexes. Figures 18 and 20 on the other hand show the plots of νasM-
O against the molecular weight of the alkyl substituent at the 4-acyl position for cobalt(11) and
zinc(11) chelates respectively. The plots show that there was a gradual increase in the metal-oxygen
stretching frequencies of the metal (11) chelates with increase in the molecular weight of the
substituent at the 4-acyl position ,resulting in increased stability of the M-O bond for the two metal
chelates. The reason for this observation has been attributed to increase in electron density around the
M-O bond with increase in the carbon chain length of the alkyl substituent at the 4-acyl position.
4.80 Conclusion
A combination of the data from UV spectra, IR and conductivity measurements shows
clearly that three different tautomeric forms of the ligand were synthesized and that
each of these ligands is behaving as a bidentate keto- enol forming neutral metal
chelates and bonding through the carbonyl oxygen and ,or that of the enolic
deprotonated hydroxyl group. The synthesis of the metal chelates with these ligands
gave quantitative yields, thus showing that these ligands are good gravimetric
reagents for magnesium, cobalt, copper and Zinc.
85
The data from the infrared spectral study of the metal chelates showed that the
carbonyl stretching frequency bands of the metal chelates increased as the length of
the carbon chain of the 4-acyl substituent increased for Magnesium (11),Cobalt (11),
and Copper (11) chelates This have been ascribed to the increase in electron density
around the C=O bond resulting in an increased bond stability and thus increase in the
carbonyl stretching frequencies of the metal chelates. A reverse trend was observed
for Zinc (11) chelates of the 4-acyl pyrazolones. Replacement of the alkyl group of
the 4-acyl substituent with the phenyl group resulted in a decrease in the carbonyl
stretching frequency bands for Mg(11),Co(11) and Cu(11) chelates ,which is as a
result of decrease in the stability of the C=O bond.
A comparative study of the infrared carbonyl and metal-oxygen stretching
frequencies of the transition metal chelates shown in table 7.0 revealed that the
νasC=O for the metal chelates did not follow the Irving Williams stability order for
transition metal complexes. While the νasM-O for the transition metal chelates of
HPMAP,HPMPRP, HPMCP,and HPMPP followed the order Cu > Co >Zn which
followed closely the Irving Williams stability order for transition metal complexes
while the νas M-O for the transition metal chelates of 4-Benzoyl pyrazolone
(HPMBP) followed the order Cu > Zn > Co which did not correspond to the Irving
Williams stability order for transition metal complexes.
86
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