Ligands: an ion or molecule capable of donating a pair of electrons to the central atom via a donor atom.
Chelating Ligands:
Werner’s Theory:
[Co(NH3)6]Cl3
Primary Valencies = 3 Cl-
Secondary Valencies = 6 NH3
Coordination Sphere = [Co(NH3)6]3-
Nomenclature of Complexes:
Ligands | Name |
Negative | |
CH3COO- | Acetato |
CN- | Cyano |
Br- | Bromo |
Cl- | Chloro |
F- | Fluoro |
OH- | Hydrido |
N3- | Nitrido |
C2O42- | Oxalato |
SO32- | Sulfito |
O2- | Superoxo |
O22- | Peroxo |
O2- | Oxo |
NH2- | Imido |
SO42- | Sulphato |
S2O32- | Thiosulfato |
HS- | Mercapto |
Positive | |
NO+ | Nitrosonium |
NH2NH3+ | Hydrazinium |
Neutral | |
H2O | Aqua |
NH3 | Ammine |
CO | Carbonyl |
CH3NH2 | Methylamine |
NO | Nitrosyl |
C5H5N | Pyridine |
Isomerism in coordination compounds
Structural Isomerism
Stereoisomerism:
a.Geometrical Isomerism: When two similar ligands are on adjacent position the isomer is called cis isomer while hen they are on opposite positions, the isomer is called trans isomer.
b.Optical Isomerism: In order to show optical isomerism, the complex should form a non superimposible mirror image which rotates the place of polarized light in opposite direction.
Valence Bond Theory:
Hybridization:
Find out the hybridization of central metal ion using following steps:
When the d orbital taking part in hybridization is inside the s and p orbital taking part in hybridization with respect to the nucleus, it is called an inner orbital complex.
Example: d2sp3 hybridization of [Co(NH3)6]3+ involves 3d, 4s and 4p orbital, hence it is an inner orbital complex.
When the d orbital taking part in hybridization outside the s and p orbital taking part in hybridization with respect to the nucleus, it is called an outer orbital complex.
Example: sp3d2 hybridization of [CoF6]3- involves 4d, 4s and 4p orbital, hence it is an inner orbital complex.
Geometry:
Coordination Number | Hybridization | Geometry |
4 | sp3 | Tetrahedral |
dsp2 | Square Planar | |
6 | d2sp3 & sp3d2 | Oct |
Magnetic Properties:
Spin:
Colour:
Compound must contain free electrons in order to show colour.
Crystal Field Theory:
Strong field ligand causes greater repulsion and thus results in the formation of low spin complexes by pairing of electrons.
Δt = (4/9) Δo
Crystal Field Stabilization Energy:
System | High Spin | Low Spin | ||
Electronic Configuration | CFSE | Electronic Configuration | CFSE | |
Octahedral Complex | ||||
d4 | t2g3 eg1 | -(3/5)Δ0 | t2g4 eg0 | -(8/5)Δ0+P |
d5 | t2g3 eg2 | 0 | t2g5 eg0 | -(10/5)Δ0+2P |
d6 | t2g4 eg2 | -(2/5)Δ0+P | t2g6 eg0 | -(12/5)Δ0+3P |
d7 | t2g5 eg2 | -(4/5)Δ0+2P | t2g6 eg1 | -(9/5)Δ0+3P |
Tetrahedral Complexes | ||||
d4 | eg2 t2g2 | -(2/5)Δt | eg4 t2g0 | -(12/5)Δt +2P |
d5 | eg2 t2g3 | 0 | eg4 t2g1 | -2 Δt +2P |
d6 | eg3 t2g3 | -(3/5)Δt +P | eg4 t2g2 | -(8/5)Δt+2P |
Magnetic Properties: Complexes with unpaired electrons are paramagnetic while with no unpaired electron are diamagnetic.
1. What are coordination compounds? |
2. How are coordination compounds named? |
3. What is the significance of coordination compounds? |
4. How do coordination compounds form coordination bonds? |
5. What are the different types of ligands in coordination compounds? |
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