Post on 16-Jan-2016
Review on Chemistry of Coordination Compounds
Coordination Compounds• Constitution
[Co(NH3)5Cl](NO3)2
Central atom Coordination number
Inner sphere
Coordination atom Outer sphere ions
ligand
H2O, NH3, Cl–, CN–, CO, SCN–, OH–
CO32-, NH2CH2CH2NH2 (ethylenediami
ne,
en), C2O42– (oxalate ion)
EDTA4 (ethylenediaminetetraacetate ion) is a hexadentate ligand.
Polydentate ligands are also known as chelating agents
Naming Coordination Compounds
• The name of a complex is one word, with no space between the ligand names and no space between the names of the last ligand and the metal.
Naming Coordination Compounds
• a salt, name the cation first • Name the ligands, in alphabetical ord
er, before the metal. Note: in anionic ligand endings from
-ide to -o , and -ate to -ato. -ite to -ito the names of the ligands differ slight
ly from their chemical namesin the chemical formula, the metal at
om or ion is written before the ligands
Naming Coordination Compounds• If the complex contains more than o
ne ligand of a particular typeUse Greek prefixes (di-, tri-, tetra-, et
c.), or bis- (2), tris-(3), tetrakis-(4), and so forth, and put the ligand name in parentheses for the later.
The ligands are listed in alphabetical order, and the prefixes are ignored in determining the order.
Naming Coordination Compounds• A Roman numeral in parentheses
follows the name of the metal to indicate the metal's oxidation state
• To name the metaluse the ending -ate if the metal is
in an anionic complex, or the Latin names for some
-ium ending for Cationic coordination sphere, or same as the element
Isomers 异构体
Compounds with the same formula but a different arrangement of atoms are called isomers.
Constitution isomers Stereoisomers
Linkage isomers
Ionization Isomer
Diastereoisomers
Enantiomers
Isom
ers
Co
NH3
NH3
NH3H3N
H3N
O
ON
Co
NH3
NH3H3N
H3N
NO O
NH3
nitro nitrito
Coordination Isomerism
[Co(NH3)6][Cr(CN)6] and [Cr(NH3)6][Co(CN)6]
[Pt(NH3)4][PtCl6] and
[Pt(NH3)4Cl2][PtCl4]
[Pt(NH3)4][PtCl4] and
[Pt(NH3)4Cl2][PtCl4]
Aquo Isomer
CrCl3·6H2O
[Cr(H2O)5Cl]Cl2·H2O
[Cr(H2O)4Cl2]Cl·2H2O
[Cr(H2O)6]Cl3
Green
Green
Violet
[Co(NH3)5Br]SO4 contains Co–Br
bond, and the sulfate ion is free
[Co(NH3)5SO4]Br contains Co–sulfate
bond, and the bromide ion is free
Ionization isomers 电 离 异 构体
two kinds of stereoisomers:
diastereoisomers 非对映异构体 enantiomers 对映异构体
Stereoisomers 立 体 异 构体
cis trans isomer
M
X
X
X
L
L L
M
X
X
X
L
L
L
FacialFac-
MeridionalMeri-
M
O
N
N
O
O
O
•Optical Isomerism 光学异构现象enantiomerschiral 手性的 achiral 非手性的The [Co(en)3]3+ cation is chiral and exists in two nonidentical mirror-image forms. properties identical except fortheir reactions with other chiral substancestheir effect on plane-polarized light: Optical Activity
Co
NN
NN
N
N
Co
NN
NN
N
N
d: dextrorotatory 右旋l: levorotatory 左旋used to indicate the direction of rotation.
•racemic 外消旋 A 50:50 mixture of both isomers
produces no net optical rotation.
•The labels
Valence Bond Theory
Vacant metalhybrid atomic orbital
Coordinate covalent bond
Occupied ligandhybrid atomic orbital
•The hybrid orbitals used by the metal are determined by the geometry of the complex.
•The number of d electrons in the metal is determined by the oxidation state of the metal ion.
•The orbitals used to construct the hybrid orbitals for bonding must be vacant on the metal.
Valence Bond Theory
•For octahedral complexes it may be necessary to pair some electrons already in d orbitals to get vacant orbitals required for hybridization. This leads to a low spin complex .
•Contrast this with the use of higher energy vacant d orbitals. This leads to more unpaired d electrons and a high spin complex.
Valence Bond Theory
•Knowing whether a complex is paramagnetic or diamagnetic can help determine which d orbitals to use. It can also help determine whether a complex is square planar or tetrahedral
Valence Bond Theory
Spectrochemical series 光化学序列
Increasing →
Weak field ligands Strong field ligands
I– < Br– < Cl– < F– < H2O < NH3 < en < CN–
Hybrid Orbitals
• A unsuccessful example:Cu(NH3)4
2+
A square planar complexHybrid form: dsp2
Cu2+ [Ar]
dsp2
•This explains the color and magnetic properties of the transition metal complexes.
•Bonding in complexes is viewed as entirely ionic and as arising from electrostatic interactions between the d electrons of the metal and the ligand electrons.
Crystal Field Theory
Crystal Field Theory• It considers the effect of the liga
nd charges on the energies of the metal ion d orbitals.
•The d orbitals are raised in energy and are separated in energy based on the geometry of the complex.
•The energy separation is called the crystal field splitting, represented by the symbol Δ.
• In octahedral complexes the dx2 - y2 and the dz2 orbitals are higher tin energy than the dxy, the dxz, and the dyz because the negative charge of the electrons from the ligands point directly at the negative charges of the electrons in the d orbitals that lie on the x,y, and z axes.
Crystal Field Theory
•The color of the complexes is due to electronic transitions from one set of d orbitals to another.
•Visible light can supply enough energy to promote an electron from the lower enegy to the higher energy orbitals.
•Light at a particular wavelength is absorbed and the complementary color is seen.
Crystal Field Theory
The angular distribution of d orbitals
Crystal Field Splitting
o = 10 Dq
Spheric field
Free atom
+6 Dq
4 Dq
o
eg
t2g
dxy, dyz, dxz
dx2-y2, dz2
Octahedral field
CFSE: Crystal Field Stabilization Energy 晶体场稳定化能
Pairing Energy 成对能 P
Tetrahedral Field
Splitting in Tetrahedral Field
t = 4/9o = 10 Dq
Spheric field
Free atom
t
e
t2
dxy, dyz, dxz
dx2-y2, dz2
Tetrahedral field
Color• Complementary colors:
• R-G
• O-B
• Y-V
•An absorbance spectrum It plots the absorbance (amount of light absorbed by a substance) as a function of wavelength
[Ti(H2O)6]3+
Spectrochemical series 光化学序列
Increasing →
Weak field ligands Strong field ligands
I– < Br– < Cl– < F– < H2O < NH3 < en < CN–
Back-bonding 反馈键
Magnetism
Paramagnetic: unpaired electronDiamagnetic: no unpaired electron
[Co(NH3)6]3+:
Co3+: d6
diamagnetic
t2g4 eg
2paramagnetic
t2g6 eg
0
[CoF6]3
Oh t2g eg
Jahn-Teller EffectsFor a non-linear molecule that is in an electronically degenerate state, distortion must occur to lower the symmetry, remove the degeneracy, and lower the energy.Jahn-Teller effects do not predict which distortion will occur other than that the center of symmetry will remain.The distortion by the unsymmetrical distribution of electrons in eg orbital is stronger than that of t2g.
Stability Constant
Cu2+ + 4NH3 [Cu(NH3)4]2+
Overall Stability ConstantStepwise stability constants: K1, K2, …, K4
Overall stability constants: 1, 2, 3, 4
Kstability = [Cu(NH3)4
2+ ][Cu2+ ] [NH3]4
1 = K1
2 = K1 K2
3 = K1 K2 K3
4 = K1 K2 K3K4
Factors That Determine The Stability Of Coordination Compounds
1. metal ions: charge, radius and electronic configuration;2. ligand: basicity, chelate effects.
Chelate Effects 螯合效应 : entropy effect.
Entropy-driven reaction (process)
[Cu(H2O)4]2+ (aq) + 2 NH3 (aq) → [Cu(NH3)2(H2O)2]2+ (aq)lg2 = 7.65
[Cu(H2O)4]2+ (aq) + en (aq) → [Cu(en)(H2O)2]2+ (aq)lg1 = 10.64
Example 1
Solution:
Ksp = [Ag+][Cl] = 1.6 × 10
Step 2:
Step 1:
Ag+ + 2NH3 = Ag(NH3)2+
AgCl(s) = Ag+ + Cl
2 =[Ag(NH3)2
+]
[Ag+][NH3]2= 1.5 × 10
Calculate the molar solubility of AgCl in a 6 M NH3 solution
Example 1 (continue)
AgCl(s) + 2NH3 = Ag(NH3)2++ Cl
Overall reaction
K =[Ag(NH3)2
+] [Cl]
[NH3]2
= (1.6 × 10)= Ksp2(1.5 × 10)
= 2.4 × 10
AgCl(s) + 2NH3 = Ag(NH3)2++ Cl
Initial (M): 6.0 0.0 0.0Change (M): -2s +s +sEqui (M): 6 - 2s s s
K = (s)(s)(6 – 2s)
s = 0.016 M
Step 3
0.1
0.045
Example 2
Calculate the equilibrium concentration of every relevant species of a 0.1 M Ag(NH3)2
+ solution.
K1 = 2.2 × 10=
K2 = 5.1 × 10=
[Ag(NH3)+]
[Ag+][NH3]
[Ag(NH3)2+]
[Ag(NH3)+][NH3]
2 =[Ag(NH3)2
+]
[Ag+][NH3]2= 1.5 × 10
With only a few exceptions, there is generally a slowly descending progression in the values of the Ki’s in any particular system.