Prof. Dr. Arafa A. M. Belal - PSU€¦ · Prof. Dr.Arafa A.M.Belal, Professor of Inorganic...

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Supervised By

Prof. Dr. Arafa A. M. Belal

Professor of Inorganic chemistry

Chemistry Department, Faculty of science,

Port Said University

An Essay

Submitted in partial fulfillment of the requirements

for the Sc. Degree in Science (Biochemistry)

Prepared By

Aya Ahmed Abd El-monem Mohamed

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ACKNOWLEDGEMENTS

ALL THANKS FOR ALLAH

I thank Allah for giving me the strength to complete such hand work.

This research project would not have been possible without the support

of many people.

I wish to express my gratitude to my supervisor,

Prof. Dr.Arafa A.M.Belal, Professor of Inorganic chemistry

Chemistry Department, Faculty of science, Port Said University

For suggesting the research point, keep continuous interest skillful

technical assistance, supervision, valuable interpretation and useful

discussion throughout the whole work. Who was abundantly helpful and

offered invaluable assistance, support and guidance.

I wish to express my love and gratitude to my beloved families; for their

understanding and endless love, through the duration of my studies.

My thanks and appreciations also go to my college in developing the

project and people who have willingly helped me out with their abilities.

My special gratitude and thanks to Prof. Ibrahim Mohy El-Deen Head

of chemistry Department and all the staff members in the chemistry

Department, Faculty of science, Port Said University, for their facilities

encourage and help.

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List of contents

Aim of investigation……………………………………………..8

-Introduction…………….…………………………………………….9

1-Electronic Energy Transition…………………………………10

2- Russel-Saunders or L-S coupling scheme……………………18

3. Term symbols………………………………………………...19

3.1. Spectroscopic terms for free ion ground states……...19

4. Total degeneracy………………………………………….......22

5. Number of microstates………………………………………..22

6. Multiple term symbols of excited states………………………24

7. Splitting of energy states……………………………………...25

7.1. Splitting of energy states corresponding to dn terms…..26

8. Energy level diagram…………………………………………27

9. Inter-electronic repulsion parameters…………………………27

9.1. Racah parameters…………………………………….27

10. Orgel diagrams………………………………………………28

11. Tanabe-Sugano diagrams……………………………………30

Experimental…………………..…………………………………….34-

1. Materials…………………………………………………35

2. Preparation of standard solutions………………………...35

3. Working procedure………………………………………35

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-Result and Discussion……….………………………………………38

1. Spectrophotometric studies………………………………….…39

2. The stoichiometry of metal – ligand complexes…………….…40

2.1. The molar ratio method………………………………....40

2.2. Conclusion……………………………………………...40

Reference...………………..……………………………………….....59-

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List of Tables

-Table (1) Term Symbols……………………………………………..21

-Table (2) Number of microstates for p2 configuration……………….23

-Table (3) Micro static of different dn configuration…………………24

-Table (4) Terms arising from dn configuration for 3d ions

(n=1 to 10)……………………………………………………………24

- Table (5) Splitting of energy sates corresponding to dn terms ……...26

- Table (6) Crystal field components of the ground and some excited

states of dn (n = 1 to 9) configuration ……………………...…….........26

-Table (7) Determination of the stoichiometry of

[Co2+

-ligand 1] complexes by molar ratio method…………..………..41


[Cu2+

-ligand 1] complexes by molar ratio method…………………….43

Table (9) Determination of the stoichiometry of -

[Ni2+

-ligand 1] complexes by molar ratio method………………...…..45


[Co2+

-ligand 2] complexes by molar ratio method………………..…..47


[Cu2+

-ligand 2] complexes by molar ratio method…….……………..49


[Ni2+

-ligand 2] complexes by molar ratio method…………...………..51

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[Co2+

-ligand 3] complexes by molar ratio method……………………53


[Cu2+

-ligand 3] complexes by molar ratio method…………………….55


[Ni2+

-ligand 3] complexes by molar ratio method………...…………..57

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List of Figures

-Figure (1) Schematic representation of the principle orbitals of the

organic compounds……………………………………………………12

-Figure (2) schematic representation of electronic absorption spectra of

complexes of first row d transition elements………………………….13

-Figure (3) Ligand to Metal Charge Transfer (LMCT) involving an

octahedral d6 complex…………………………………………………15

- Figure (4) Metal to Ligand Charge Transfer (MLCT) involving an

octahedral d5 complex………………………………………………....16

-Figure (5) D Orgel diagram…………………………………………..28

-Figure (6) F Orgel diagram…………………………………………...29

- Figure (7) Tanabe-Sugano diagram for d2 octahedral complexes…...31

-Figure (8) Tanabe-Sugano diagram for d3 octahedral complexes……32

- Figure (9) spectrophotometer instrument……………………………36

-Figure (10) color plates……………………………………………….36

- Figure (11) Molar ratio method for [Co2+

] = 1×10-2

M,

[Ligand 1] = 1×10-2

M…………………………………………….…...42

- Figure (12) Molar ratio method for [Cu2+

] = 1×10-2

M,

[Ligand 1] = 1×10-2

M ………………………………………………...44

- Figure (13) Molar ratio method for [Ni2+

] = 1×10-2

M,

[Ligand 1] = 1×10-2

M ……………………………………………..….46


] = 1×10-2

M,

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[Ligand 2] = 1×10-2

M……………………………………...………….48

- Figure (15) Molar ratio method for [Cu2+

] = 1×10-2

M,

[Ligand 2] = 1×10-2

M …………………………………………….….50

- Figure (16) Molar ratio method for [Ni2+

] = 1×10-2

M,

[Ligand 2] = 1×10-2

M ………………………………………………...52


] = 1×10-2

M,

[Ligand 3] = 1×10-2

M ………………………………………………...54

-Figure (18) Molar ratio method for [Cu2+

] = 1×10-2

M,

[Ligand 3] = 1×10-2

M ………………………………………………...56

-Figure (19) Molar ratio method for [Ni2+

] = 1×10-2

M,

[Ligand 3] =1×10-2

M ......……………………………………………..58

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Aim of Investigation

The aim of this work is make an essay of electronic

spectra.

And do applied research on metal complexes formed by

some ligands with some metal ions (Cu, Co, Ni) applying

the spectrometry studies (Ultra violet, visible spectra) in

solution by using molar ratio method.

2S+1LJ

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1. Electronic Energy Transition:

1.1 Introduction

Spectra are broadly classified into two groups (i) emission spectra and

(ii) absorption spectra.

1.2. Types of spectra

i. Emission spectra:

Emission spectra are of three kinds (a) continuous spectra, (b) band

spectra and (c) line spectra.

Continuous spectra:

Solids like iron or carbon emit continuous spectra when they are heated

until they glow.

Continuous spectrum is due to the thermal excitation of the molecules

of the substance.

Band spectra:

The band spectrum consists of a number of bands of different colors

separated by dark regions.

The bands are sharply defined at one edge called the head of the band

and shade off gradually at the other edge. Band spectrum is emitted by

substances in the molecular state when the thermal excitement of the

substance is not quite sufficient to break the molecules into continuous

atoms.

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Line spectra:

A line spectrum consists of bright lines in different regions of the visible

spectrum against a dark background. All the lines do not have the same

intensity. The number of lines, their nature and arrangement depends on

the nature of the substance excited. Line spectra are emitted by vapours

of elements. No two elements do ever produce similar line spectra.

ii. Absorption spectra:

Electronic absorption spectrum is of two types. d-d spectrum and charge

transfer spectrum. d-d spectrum deals with the electronic transitions

within the d-orbitals. In the charge – transfer spectrum, electronic

transitions occur from metal to ligand or vice-versa. [1]

Ultraviolet-visible spectroscopy (UV = 200-38Q nm, visible = 380-780

nm) corresponds to electronic excitations between the energy levels that

correspond to the molecular orbitals of the systems. The lowest energy

transition is that between the highest occupied molecular orbital

(HOMO) and the lowest unoccupied molecular orbital (LUMO) in the

ground state. The absorption of electromagnetic radiation excites an

electron to the LUMO and creates an excited state. When continuous

radiation passes through a transparent material, a portion of

radiation may be absorbed and excites an electron to the LUMC

creating an excited state and the residual radiation, when it is passed

through a prism, will yield a spectrum with gaps in it. This is called an

absorption spectrum. The most important modes of electronic energy

change, which occur when radiation in the UV or visible region is

absorbed by organic molecule, are summarized below [2]

:

(A)Transition between bonding sigma to antibonding sigma(𝛔 − 𝛔∗).

The excitation of σ-electrons is only brought about by the absorption of

short-wave (high-energy) radiation: compounds containing only

σ-valence electrons (saturated compounds).

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(B)Transition between bonding pi to antibonding pi (𝛑 − 𝛑∗).

The excitation of π -electrons give intense absorption bands in the range

200-300 nm (ε = 100 − 3000mol−1cm−1dm3) appears in the range

200-300 nm for all compounds.

(C) Promotion of non-bonding electrons (unshared pairs) into

antibonding sigma (n-𝛔∗) or antibonding pi (n- π *) orbitals. The medium intense (n- 𝛔 *) band appears in the range 200-300 nm for

all compounds except alcohols and ethers it appears below 185 nm. The

(n -π∗) transitions is a weak absorption band in the range 270-350nm

(10-200mol−1cm−1dm3).

Figure (1) Schematic representation of energy of the principal orbitals of the organic compound.

The absorption spectrum of transition metal-complexes has beaks that

usually fall into two reasonably clear-cut categories.[3]

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1- Relatively, weak peaks found in the visible region are attributed to

d − d transitions (ε = 1 − 50mol−1cm−1dm3), since they result from

transition of an electron from one d orbital to another.

2-The more intense bands that are mostly found at shorter wavelengths are also associated with transition of electrons from one energy level to another, but the orbital's representing ground and excited states are normally associated with different parts of the complex (this process called Charge transfer; CT).

3- In addition to d-d and CT bands the spectrum may show bands (generally intense in the ultraviolet region) that can be attributed to the transitions between orbitals involving only the ligands; the positions of such bands will be similar to those found in the spectra of uncoordinated ligands.

Figure (2) Schematic representation of electronic absorption spectra of complexes of first row d transition elements.

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(D) Charge - Transfer Absorption:

Ligand to Metal and Metal to Ligand Charge

Transfer Bands.

Many inorganic species show charge-transfer absorption and are

donor to an orbital associated with the acceptor.

Molar called charge-transfer complexes. For a complex to

demonstrate charge-transfer behavior, one of its components

must have electron donating properties and another component

must be able to accept electrons. Absorption of radiation then

involves the transfer of an electron from the absorbtivities from

charge-transfer absorption are large (greater that 10,000 L mol-

1 cm-1

). [4]

Ligands possess σ, σ*, π, π*, and nonbonding (n) molecular

orbitals. If the ligand molecular orbitals are full, charge transfer

may occur from the ligand molecular orbitals to the empty or

partially filled metal d-orbitals. The absorptions that arise from

this process are called ligand-to-metal charge-transfer bands

(LMCT). LMCT transitions result in intense bands. Forbidden d-

d transitions may also take place giving rise to weak absorptions.

Ligand to metal charge transfer results in the reduction of the

metal.

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Figure (3) Ligand to Metal Charge Transfer (LMCT) involving

an octahedral d6 complex.

[5]

If the metal is in a low oxidation state (electron rich) and the

ligand possesses low-lying empty orbitals

(e.g., COCO or CN−CN−) then a metal-to-ligand charge transfer

(MLCT) transition may occur. LMCT transitions are common for

coordination compounds having π-acceptor ligands. Upon the

absorption of light, electrons in the metal orbitals are excited to

the ligand π* orbitals. Figure 3 illustrates the metal to ligand

charge transfer in a d5 octahedral complex. MLCT transitions

result in intense bands. Forbidden d – d transitions may also

occur. This transition results in the oxidation of the metal.

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Figure (4) Metal to Ligand Charge Transfer (MLCT) involving

an octahedral d5 complex.

[6]

(E) Electronic spectra of transitions metal complexes

(d-d) transition.

Electronic absorption spectroscopy requires consideration of the

following principles:

a. Franck-Condon Principle:

Electronic transitions occur in a very short time (about 10-15

sec.) and hence the atoms in a molecule do not have time to

change position appreciably during electronic transition .So the

molecule will find itself with the same molecular configuration

and hence the vibrational kinetic energy in the exited state

remains the same as it had in the ground state at the moment of

absorption.

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b. Electronic transitions between vibrational states:

Frequently, transitions occur from the ground vibrational level of

the ground electronic state to many different vibrational levels of

particular excited electronic states. Such transitions may give rise

to vibrational fine structure in the main peak of the electronic

transition. Since all the molecules are present in the ground

vibrational level, nearly all transitions that give rise to a peak in

the absorption spectrum will arise from the ground electronic

state. If the different excited vibrational levels are represented as

υ1, υ2, etc., and the ground state as υ0, the fine structure in the

main peak of the spectrum is assigned to υ0 → υ0, υ0 → υ1, υ0

→ υ2 etc., vibrational states. The υ0 → υ0 transition is the

lowest energy (longest wave length) transition.

c. Symmetry requirement:

This requirement is to be satisfied for the transitions discussed

above.

Electronic transitions occur between split ‘d’ levels of the central

atom giving rise to so called d-d or ligand field spectra. The

spectral region where these occur spans the near infrared, visible

and U.V. region. [7]

Ultraviolet( UV ) Visible( Vis ) Near infrared( NIR)

50,000 - 26300 26300 -12800 12800 -5000 cm-1

200 - 380 380 -780 780 - 2000 nm

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S coupling scheme:-Saunders or L-Russel .2

An orbiting electronic charge produces magnetic field

perpendicular to the plane of the orbit. Hence the orbital angular

momentum and spin angular momentum have corresponding

magnetic vectors. As a result, both of these momenta couple

magnetically to give rise to total orbital angular momentum.

There are two schemes of coupling: Russel- Saunders or L-S

coupling and j-j coupling.

a. The individual spin angular momenta of the electrons, si, each

of which has a value of ±½, combine to give a resultant spin

angular momentum (individual spin angular momentum is

represented by a lower case symbol whereas the total resultant

value is given by a upper case symbol).

si = S

Two spins of each ± ½ could give a resultant value of S =1 or S =

0; similarly a resultant of three electrons is 1 ½ or ½ .The

resultant is expressed in units of h/2π.

The spin multiplicity is given by (2S+1). Hence, If n is the

number of unpaired electrons, spin multiplicity is given by n + 1.

b. The individual orbital angular momenta of electrons, li, each

of which may be 0, 1, 2, 3, 4 ….. in units of h/2π for s, p, d, f, g,

…..orbitals respectively, combine to give a resultant orbital

angular momentum, L in units of h/2π. Σ li = L

The resultant L may be once again 0, 1, 2, 3, 4…. which are

referred to as S, P, D, F G,… respectively in units of h/2π.The

orbital multiplicity is given by (2L+1).

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0 1 2 3 4 5

S P D F G H

c. Now the resultant S and L couple to give a total angular

momentum, J. Hence, it is not surprising that J is also quantized

in units of h/2π.

The possible values of S, L, J quantum numbers are given as:

S= (s1+s2), (s1+s2-1), (s1+s2-2),……… |s1-s2|

L = (l1+l2), (l1+l2-1), (l1+l2-2),……….………..|l1-l2|

J = L + S , L + S - 1 , L + S - 2 , L + S - 3 ,.…..| L – S|

The symbol | | indicates that the absolute value (L – S) is

employed, i.e., no regard is paid to ± sign. Thus for L = 2 and S =

1, the possible J states are 3, 2 and 1 in units of h/2π.

The individual spin angular momentum, si and the individual

orbital angular momentum, li, couple to give total individual

angular momentum, ji. This scheme of coupling is known as

spin-orbit coupling or j -j coupling.[8]

:Term symbols .3

3.1. Spectroscopic terms for free ion ground states

The rules governing the term symbol for the ground state

according to L-S coupling scheme are given below:

a. The spin multiplicity is maximized i.e., the electrons occupy

degenerate orbitals so as to retain parallel spins as long as

possible (Hubnd’s rule).

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b. The orbital angular momentum is also maximized i.e., the

orbitals are filled with highest positive m values first.

c. If the sub-shell is less than half-filled, J = L– S and if the sub-

shell is more than half – filled, J = L +S.

The term symbol is given by 2S+1

LJ. The left-hand superscript

of the term is the spin multiplicity, given by 2S+1 and the right-

hand subscript is given by J. It should be noted that S is used to

represent two things- (a) Total spin angular momentum and

(b) And total angular momentum when L = 0. The above rules

are illustrated with examples. [9]

For d4 configuration:

Hence, L = 3 -1 = 2 i.e., D; S = 2; 2S+1 = 5; and J = L- S = 0;

Term symbol = 5D0

For d9 configuration:

Hence, L = +2+1+0-1 = 2 i.e., D; S = 1 /2; 2S+1 = 2; and J = L+

S = 3/2; Term symbol = 2D5/2

Spin multiplicity indicates the number of orientations in the

external field. If the spin multiplicity is three, there will be three

orientations in the magnetic field. Parallel, perpendicular and

opposed. There are similar orientations in the angular momentum

in an external field.

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The spectroscopic term symbols for dn configurations are given

in the Table-1. The terms are read as follows: The left-hand

superscript of the term symbol is read as singlet, doublet ,triplet,

quartet, quintet, sextet, septet, octet, etc., for spin multiplicity

values of 1, 2, 3, 4, 5, 6,7, 8, etc., respectively.1S0 (singlet S

nougat); 2S1/2 (doublet S one–half); 3

P2 (triplet P two ); 5I8(quintet I

eight). It is seen from the Table-1 that dn and d

10-n have same term

symbols, if we ignore J values. Here n stands for the number of

electrons in dn configuration.

Table 1.Term symbols

It is also found that empty sub -shell configurations such as p0, d

0,

f0, etc., and full filled subshell configurations such as p

6, d

10, f

14, etc.,

have always the term symbol 1S0 since the resultant spin and

angular momenta are equal to zero. All the inert gases have term

symbols for their ground state 1S0 .Similarly all alkali metals

reduce to one electron problems since closed shell core

contributes nothing to L , S and J; their ground state term symbol

is given by 2S1/2. Hence d electrons are only of importance in

deciding term symbols of transition metals. [10]

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4. Total degeneracy:

We have seen that the degeneracy with regard to spin is its

multiplicity which is given by (2S+1). The total spin multiplicity

is denoted by Ms running from S to -S. Similarly orbital

degeneracy, ML, is given by (2L+1) running from L to -L. For

example, L = 2 for D state and so the orbital degeneracy is

(2x2+1) =5 fold. Similarly, for F state, the orbital degeneracy is

seven fold. Since there are (2L+1) values of ML, and (2S+1)

values of Ms in each term, the total degeneracy of the term is

given by: 2(L+1)(2S+1).

Each value of ML occurs (2S+1) times and each value of Ms

occurs (2L+1) times in the term.

For 3F state, the total degeneracy is 3x7 = 21 fold and for the

terms 3P,

1G,

1D,

1S, the total degeneracy is 9,9,5,1 fold

respectively. Each fold of degeneracy represents one

microstate.[11]

5. Number of microstates:

The electrons may be filled in orbitals by different arrangements

since the orbitals have different ml values and electrons may also

occupy singly or get paired. Each different type of electronic

arrangement gives rise to a microstate. Thus each electronic

configuration will have a fixed number of microstates. The numbers

of microstates for p2 configuration are given in Table-2 (for both

excited and ground states). [12]

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Table 2. Number of microstates for p2 configuration

Each vertical column is one micro state. Thus for p2 configuration,

there are 15 microstates. In the above diagram, the arrangement of

singlet states of paired configurations given in A(see below) is not

different from that given in B and hence only one arrangement for

each ml value.

The number of microstates possible for any electronic configuration

may be calculated from the formula,

Number of microstates = n! / r! (n - r)!

Where n is the twice the number of orbitals, r is the number of

electrons and ! is the factorial.

For p2 configuration, n= 3x2 =6; r = 2; n – r = 4

6! = 6 x 5 x 4 x 3 x 2 x 1 = 720; 2! = 2 x 1 = 2; 4! = 4 x 3 x 2 x 1 = 24

Substituting in the formula, the number of microstates is 15.

The number of microstates is also given by

n=m π 2(2L+1) –N+1/ N

n=1

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6. Multiple term symbols of excited states:

The terms arising from dn configuration for 3d metal ions are given

Table-4

Table 4. Terms arising from dn configuration for 3d ions (n=1 to10)

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7. Splitting of energy states: The symbols A (or a) and B (or b) with any suffixes indicate wave

functions which are singly degenerate. Similarly E (or e) indicates double

degeneracy and T (or t) indicates triple degeneracy. Lower case symbols,

a1g, a2g, eg, etc., are used to indicate electron wave functions(orbitals) and

upper case symbols are used to describe electronic energy levels.

Thus 2T2g means an energy level which is triply degenerate with respect to

orbital state and also doubly degenerate with respect to its spin state.

Upper case symbols are also used without any spin multiplicity term and

they then refer to symmetry (ex., A1g symmetry). The subscripts g and u

indicate gerade (even) and ungerade (odd).

Splitting of D state parallels the splitting of d orbitals and splitting of F

state splits parallels splitting of f orbitals. For example, F state splits into

either T1u, T2u and A2u or T1g, T2g and A2g sub-sets.

Which of these is correct is determined by g or u nature of the

configuration from which F state is derived. Since f orbitals are u in

character 2F state corresponding to f

1 configuration splits into

2T1u,

2T2u, and

2A2u components; similarly

3F state derived from d

2

configuration splits into 3T2g,

3T1g and

3A2g components because d

orbitals are g in character.[13]

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7.1. Splitting of energy states corresponding to dn terms

These are given in Table-6.

Table 5. Splitting of energy states corresponding to d

n terms.

The d-d spectra is concerned with dn configuration and hence the

crystal field sub-states are given for all the dn configuration in

Table 6.

Table 6. Crystal field components of the ground and some excited

states of dn (n=1 to 9) configuration.

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8. Energy level diagram:

Energy Level Diagrams are described by two independent

schemes - Orgel Diagrams which are applicable to weak field

complexes and Tanabe –Sugano (or simply T-S) Diagrams which

are applicable to both weak field and strong field complexes.

9. Inter-electronic repulsion parameters:

The inter-electronic repulsions within a configuration are linear

combinations of Coulombic and exchange integrals above the

ground term. They are expressed by either of the two ways:

Condon – Shortly parameters, F0, F2 and F4 and Racah

parameters, A, B and C. The magnitude of these parameters

varies with the nature of metal ion.

9.1. Racah parameters

The Racah parameters are A, B and C. The Racah parameter A

corresponds to the partial shift of all terms of a given electronic

configuration. Hence in the optical transition considerations, it is

not taken into account. The parameter, B measures the inter

electronic repulsion among the electrons in the d-orbitals. The

decrease in the value of the interelectronic repulsion parameter,

B leads to formation of partially covalent bonding.

The ratio between the crystal B1 parameter and the free ion B

parameter is known as nephelauxetic ratio and it is denoted by β.

The value of β is a measure of covalency.

The smaller the value, the greater is the covalency between the

metal ion and the ligands. The B and C values are a measure of

spatial arrangement of the orbitals of the ligand and the metal

ion. [14]

29

10. Orgel diagrams:

Orgel diagrams are useful for showing the energy levels of both high

spin octahedral and tetrahedral transition metal ions. They ONLY

show the spin-allowed transitions. For complexes with D ground

terms only one electronic transition is expected and the transition

energy corresponds directly to D. Hence, the following high spin

configurations are dealt with: d1, d

4, d

6 and d

9. [15]

Figure (5) D Orgel diagram

On the left hand side d1, d

6 tetrahedral and d

4, d

9 octahedral

complexes are covered and on the right hand side d4, d

9 tetrahedral

and d1, d

6 octahedral. For simplicity, the g subscripts required for the

octahedral complexes are not shown.

For complexes with F ground terms, three electronic transitions are

expected and D may not correspond directly to transition energy. The

following configurations are dealt with: d2, d

3 high spin d

7and d

8. [16]

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Figure (6) F Orgel diagram

On the left hand side d2, d

7 tetrahedral and d

3, d

8 octahedral

complexes are covered and on the right hand side d3, d

8 tetrahedral

and d2 and high spin d

7 octahedral. Again for simplicity, the g

subscripts required for the octahedral complexes are not shown. [17]

On the left hand side, the first transition corresponds to D, the

equation to calculate the second contains expressions with both D and

C.I. (the configuration interaction from repulsion of like terms) and

the third has expressions which contain D, C.I. and the Racah

parameter B.[18]

31

11. Tanabe-Sugano diagrams:

An alternative method is to use Tanabe Sugano diagrams, which

are able to predict the transition energies for both spin-allowed

and spin-forbidden transitions, as well as for both strong field

(low spin), and weak field (high spin) complexes. Note however

that most textbooks only give Tanabe-Sugano diagrams for

octahedral Complexes and a separate diagram is required for

each configuration.

In this method the energy of the electronic states are given on the

vertical axis and the ligand field strength increases on the

horizontal axis from left to right. Linear lines are found when

there are no other terms of the same type and curved lines are

found when 2 or more terms are repeated. This is as a result of

the "non-crossing rule". The baseline in the Tanabe-Sugano

diagram represents the lowest energy or ground term state. [19]

Example 1: The d2 case (not many examples documented)

The electronic spectrum of the V3+

ion, where V(III) is doped

into alumina (Al2O3), shows three major peaks with frequencies

of: n1 = 17400 cm-1, n2 = 25400 cm-1

and n3 = 34500 cm-1

.

These have been assigned to the following spin-allowed

transitions.

3T2g <---

3T1g

3T1g (P) <---

3T1g

3A2g <---

3T1g

The ratio between the first two transitions is calculated as n2 / n1

which is equal to 25400 / 17400 = 1.448.

In order to calculate the Racah parameter, B, the position on the

horizontal axis where the ratio between the lines representing n2

32

and n1 is equal to1.448, has to be determined. On the diagram

below, this occurs at D/B = 30.9. Having found this value, a

vertical line is drawn at this position. [20]

Tanabe-Sugano diagram for d2 octahedral

complexes [21]

Figure (7)

33

On moving up the line from the ground term to where lines from the

other terms cross it, we are able to identify both the spin-forbidden

and spin- allowed transition and hence the total number of transitions

that are possible in the Electronic spectrum. [22]

Next, find the values on the vertical axis that correspond to the spin-

allowed transitions so as to determine the values of n1/B, n2/B and

n3/B. From the diagram above these are 28.78, 41.67 and 59.68

respectively. [23]

Knowing the values of n1, n2 and n3, we can now calculate the value

of B.

Since n1/B = 28.78 and n1 is equal to 17,400 cm-1

, then

B = n1/28.78 = 17400/28.78 or B = 604.5cm-1

Then it is possible to calculate the value of D. Since D/B = 30.9,

then: D = B*30.9 and hence: D = 604.5*30.9 = 18680 cm-1

. [24]

Example 1: The d3 case

We can Calculate the value of B and D for the Cr3+

ion in

[Cr(H2O)6)]3+

if n1 = 17000 cm-1

, n2 = 24000 cm-1

and n3 = 37000

cm-1

.

These values have been assigned to the following spin-allowed

transitions.

4T2g <---

4A2g

4T1g <---

4A2g

4T1g (p) <---

4A2g

From the information given, the ratio n2 / n1 = 24000 / 17000 =

1.412[25]

Using a Tanabe-Sugano diagram for a d3 system this ratio is found at

D/B = 24.0[26]

34

Tanabe-Sugano diagram for d3 octahedral

complexes

Figure (8)

35

Interpolation of the graph to find the Y-axis values for the spin-

allowed transitions gives:

. n1/B = 24.00

.n2/B = 33.90

.n3/B = 53.11

Recall that n1 = 17000 cm-1

. Therefore for the first spin-allowed

transition,

17000 /B = 24.00 from which B can be obtained, B = 17000 / 24.00

or B = 708.3 cm-1

.

This information is then used to calculate D. [27]

Since D / B = 24.00 then D = B*24.00 = 708.3 * 24.00 = 17000

cm-1

. [28]

It is observed that the value of Racah parameter B in the complex is

708.3 cm-1

and n3 = 37000 cm1,while the value of B in the free Cr3+

ion is 1030 cm-1

. This shows a 31% reduction in the Racah parameter

indicating a strong Nephelauxetic effect.[29]

The Nephelauxetic Series is as follows:

F->H2O>urea>NH3 >en~C2O42- >NCS- >Cl-~CN->Br >S2- ~I-.

Ionic ligands such as F- give small reduction in B, while covalently

bonded ligands such as I- give a large reduction in B. [30]

37

1. Materials

The starting chemicals were of analytical grade and were used

without further purification.

2. Preparation of standard solutions:

a- Metal ion solution

A (1× 10−2)M of metal ion solution was prepared by dissolving an

accurately weighed appropriate amount of a grade metal chloride in

ethyl alcohol.

b- Ligand solution

A (1× 10−2)M of ligand solution was prepared by dissolving an

appropriate quantity of this compound in ethyl alcohol.

3. Working procedure Ultraviolet / Visible Spectroscopic Measurements:

In the present work, the metal ion was mixed with ligand solution in a

10 ml volumetric flask, then the volume was completed to the mark with ethanol. Blank solution was prepared by taking the same

concentration of ethanol only. The UV /visible spectral measurements at 30°C were recorded using a Jenway Model 6800

spectrophotometer Flight Deck (COM!: 6507006), which recorded A versus wavelength of light absorbed (A = 200-800 nm).

[31]

38

Figure (9) [32]

Figure (10) [33]

The spectrophotometric methods applied are:

a-The molar ratio method recommended by Yoe and Jones[34]

. b- The straight line method due to Asmus

[35].

c- The continuous variation method by Job

[36].

40

1. Spectrophotometric studies:

Transition metals form coordinate covalent bonds with Lewis bases to

make coordination complexes. The anion or neutral compound reacting

with the metal are called ligands.[37]

The experiment the Mole Ratio and Slope Ratio methods were used to

determine the ligand/metal ratio. The stoichiometric coefficients for the

metal and ligand were determined using the Mole Ratio Method. For the

Mole Ratio method, multiple solutions were prepared. The concentrations

of the metal were constant while the ligand concentrations were varied.

At lower concentrations of ligand there were insufficient amounts to form

maximum amounts of complex; the ligand was the limiting reagent. As

the concentration of ligand was increased, so did the absorbance of the

complex. The absorption will increase until the stoichiometric amount

ligand has been added for a specific amount metal. Once the

stoichiometric amount of ligand was added the absorbance of the

complex will plateau. The point where the two linear portions of the

graph intercept is the stoichiometric ratio of ligand/metal.[38]

In the Slope Ratio method the absorbance was measured with the ligand

concentration being held constant in one trial, and the metal concentration

being held constant in the other trial. According to Beers Law [39]

, when

the absorbance is plotted as a function of the ligand concentration, with

excess metal, a linear relationship is obtained.

41

2. The stoichiometry of metal – ligand complex:

Since organometallic complexes in general show selective

absorption in the visible or ultra violet, this property is widely

employed to determine their composition as will as their

stability constants. The stoichiometry of a stable complex can be

determined by either of three related technique: [40]

2.1. The molar ratio method :

The molar ratio method introduced by yoe and jones.[34]

In this

method , the absorbance s are measured for a series of solutions

which contain varying amounts of one constituent with a

constant amount of absorbance as a function of a ratio of moles

of reagent to moles of metal ion . This is expected to give

straight line from the origin to the point where equivalent

amounts of the constituents are present. The curve will then

become horizontal, because all of one constituent is used up and

the addition of more of the other constituent can produce no

more of the absorbing complex. If the constituent in excess itself

absorbs at the same wave length, the curve after the equivalence

point will show a slope that is positive, but of smaller magnitude

than that prior to equivalence.

2.2. Conclusion

In the present study the metal ions was kept constant at 1×10-

2M, The molar ratio [L] / [M] relationship is recorded in the

following tables.

And represented graphically in the following figures. All figures

show two straight portions intersecting at [L] / [M]. This

indicates the probable formation of complexes having the

composition (1 Metal: 1 Ligand) and (1 Metal: 2 Ligand).

42

Ligand (1)and Metal (Co):

Table (7) Determination of the stoichiometry of [Co2+

- ligand 1]

complexes by molar ratio method.

[𝐿]

[𝑀] λmax(nm) [A] [L] [M]

0.25 293 0.16 0.025 0.1

0.5 291 0.322 0.05 0.1

0.75 291 0.456 0.075 0.1

1 286 0.653 0.1 0.1

1.25 291 0.829 0.125 0.1

1. 5 291 1.042 0.150 0.1

1.75 291 1.155 0.175 0.1

2 289 1.383 0.2 0.1

2.25 289 1.572 0.225 0.1

2.5 289 0.861 0.250 0.1

2.75 289 2.008 0.275 0.1

3 289 2.053 0.3 0.1

43

Figure (11) Molar ratio method for [Co2+

] = 1×10-2

M,

[Ligand 1] = 1×10-2

M.

0

0.5

1

1.5

2

2.5

0.25 0.5 0.75 1 1.25 1 .5 1.75 2 2.25 2.75 3

Ab

sorb

ance

[L]/[m]

44

Ligand (1) and metal (Cu):

Table (8) Determination of the stoichiometry of [Cu2+

- ligand 1]


[𝐿]


0.25 293 0.139 0.025 0.1

0.5 291 0.358 0.05 0.1

0.75 291 0.457 0.075 0.1

1 291 0.572 0.1 0.1

1.25 289 0.686 0.125 0.1

1. 5 289 0.626 0.150 0.1

1.75 289 0.943 0.175 0.1

2 289 1.139 0.2 0.1

2.25 288 1.15 0.225 0.1

2.5 288 1.391 0.250 0.1

2.75 288 1.536 0.275 0.1

3 288 1.545 0.3 0.1

45

Figure (12) Molar ratio method for [Cu2+

] =1×10-2

M,

[Ligand 1]=1×10-2

M.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0.25 0.5 0.75 1 1.25 1.75 0.2 2.225 0.25 2.75 3

Ab

sorb

ance

[L]/[m]

46

Ligand (1) and metal (Ni):

Table (9) Determination of the stoichiometry of [Ni2+

- ligand 1]


[𝐿]


0.25 293 0.102 0.025 0.1

0.5 291 0.219 0.05 0.1

0.75 291 0.403 0.075 0.1

1 289 0.5 0.1 0.1

1.25 289 0.622 0.125 0.1

1. 5 289 0.925 0.150 0.1

1.75 289 1.014 0.175 0.1

2 289 1.19 0.2 0.1

2.25 289 1.425 0.225 0.1

2.5 286 1.485 0.250 0.1

2.75 286 1.718 0.275 0.1

3 286 1.795 0.3 0.1

47

Figure (13) Molar ratio method for [Ni2+

] = 1×10-2

M,

[Ligand 1]=1×10-2

M.

48

Ligand (2) and metal (Co):

Table (10) Determination of the stoichiometry of

[Co2+

- ligand 2] complexes by molar ratio method.

[𝐿]


0.25 294 0.136 0.025 0.1

0.5 314 0.194 0.05 0.1

0.75 293 0.285 0.075 0.1

1 316 0.365 0.1 0.1

1.25 312 0.575 0.125 0.1

1. 5 305 0.695 0.150 0.1

1.75 305 0.825 0.175 0.1

2 305 0.896 0.2 0.1

2.25 305 1.004 0.225 0.1

2.5 305 1.143 0.250 0.1

2.75 305 1.308 0.275 0.1

3 305 1.365 0.3 0.1

49


] = 1×10-2

M,

[Ligand 2] = 1×10-2

M.

50

Ligand (2) and metal (Cu) :


[Cu2+


[𝐿]


0.25 293 0.117 0.025 0.1

0.5 292 0.148 0.05 0.1

0.75 293 0.146 0.075 0.1

1 294 0.216 0.1 0.1

1.25 329 0.453 0.125 0.1

1. 5 323 0.503 0.150 0.1

1.75 326 0.626 0.175 0.1

2 308 0.702 0.2 0.1

2.25 308 0.46 0.225 0.1

2.5 308 1 0.250 0.1

2.75 308 1.18 0.275 0.1

3 308 1.188 0.3 0.1

51


] = 1×10-2

M,

[Ligand 2] =1×10-2

M.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0.25 0.5 0.75 1 0.125 1.5 1.75 2 2.5 2.75 3

Ab

sorb

ance

[L]/[m]

52



[Ni2+


[𝐿]


0.25 293 0.11 0.025 0.1

0.5 294 0.191 0.05 0.1

0.75 294 0.322 0.075 0.1

1 306 0.445 0.1 0.1

1.25 306 1.653 0.125 0.1

1. 5 306 1.934 0.150 0.1

1.75 306 1.831 0.175 0.1

2 306 1.898 0.2 0.1

2.25 306 2.045 0.225 0.1

2.5 306 2.088 0.250 0.1

2.75 305 2.162 0.275 0.1

3 306 2.26 0.3 0.1

53


] = 1×10-2

M,

[Ligand 2] = 1×10-2

M.

0

0.5

1

1.5

2

2.5

0.25 0.5 0.75 1 0.125 1.75 2 2.25 2.5 2.75 3

Ab

sorb

ance

[L]/[m]

54

Ligand (3) and metal (Co):

[𝐿]


0.25 293 0.299 0.025 0.1

0.5 292 0.542 0.05 0.1

0.75 291 0.998 0.075 0.1

1 291 1.053 0.1 0.1

1.25 291 1.369 0.125 0.1

1. 5 291 1.675 0.150 0.1

1.75 291 1.863 0.175 0.1

2 291 2 0.2 0.1

2.25 291 2.217 0.225 0.1

2.5 291 2.481 0.250 0.1

2.75 292 2.564 0.275 0.1

3 293 2.691 0.3 0.1


[Co2+


55


] =1×10-2

M,

[Ligand 3] =1×10-2

M.

56

Ligand (3) and metal (CU):

[𝐿]


0.25 292 0.395 0.025 0.1

0.5 292 0.629 0.05 0.1

0.75 291 1.941 0.075 0.1

1 286 1.126 0.1 0.1

1.25 291 1.412 0.125 0.1

1. 5 291 1.711 0.150 0.1

1.75 291 1.965 0.175 0.1

2 291 2.126 0.2 0.1

2.25 291 2.385 0.225 0.1

2.5 291 2.481 0.250 0.1

2.75 292 2.538 0.275 0.1

3 293 2.594 0.3 0.1


[Cu2+


57


] =1×10-2

M,

[Ligand 3] = 1×10-2

M.

58



[Ni2+


[𝐿]

[𝑀] λmax(n

m)

[A] [L] [M]

0.25 292 0.307 0.025 0.1

0.5 292 0.566 0.05 0.1

0.75 291 0.827 0.075 0.1

1 291 1.171 0.1 0.1

1.25 291 1.327 0.125 0.1

1. 5 291 1.614 0.150 0.1

1.75 291 1.898 0.175 0.1

2 291 2.146 0.2 0.1

2.25 291 2.295 0.225 0.1

2.5 291 2.436 0.250 0.1

2.75 292 2.633 0.275 0.1

3 293 2.787 0.3 0.1

59


] = 1×10-2

M,

[Ligand 3] = 1×10-2

M.

60

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61

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http://www.epolin.com/beer-lambert-law

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