Page 1 - Microsoft Word - Lesson note-2(coordination compounds)

SUBJECT-CHEMISTRY

CHAPTER-COORDINATION COMPOUNDS

SUBTOPIC- Isomerism, Werner's coordination theory,VBT.

KEY NOTES:

 Ionisation isomerism: ionizes different ions.
[Co(NH ) Br]SO and [Co(NH ) SO ]Br
3 5
4
3 5
4
 Solvate isomerism: It is isomerism in which solvent is involved
as ligand e.g. [Cr(H O) ]Cl ,[Cr Cl(H O) ]Cl .H O,[Cr Cl (H O) ]Cl .2H O
2
5
2
3
6
2
4
2
2
2
2
2
 Co-ordination isomerism- when both cations and anions are
complexes and they differ in the co-ordination of ligands.
[Co(NH ) ][Cr (C O ) ], [Cr(NH ) ][Co(C O ) ]
4 3
3 6
2
3 6
2
4 3
 Linkage isomerism: the isomerism in which a ligand can turn
linkage with metal through different atoms.
e.g. [Co(NH ) ONO ]Cl
3 5
2
[Co(NH ) NO ]Cl 2
2
3 5
 Werner in 1898, propounded his theory of coordination compounds.
The main postulates are:
1. In coordination compounds metals show two types of linkages
(valences)-primary and secondary.
2. The primary valences are normally ionisable and are satisfied by
negative ions.
3. The secondary valences are non ionisable. These are satisfied by
neutral molecules or negative ions. The secondary valence is equal
to the coordination number and is fixed for a metal.
4. The ions/groups bound by the secondary linkages to the metal have
characteristic spatial arrangements corresponding to different
coordination numbers.
 The valence bond theory (VBT) explains with reasonable success, the
formation, magnetic behavior and geometrical shapes of co-ordination
compounds. It fails to provide a quantitative interpretation of
magnetic behavior and has nothing to say about the optical properties
of these compounds.
 According to this theory, the metal atom or ion under the influence of
ligands can use its (n-1)d, ns, np or ns, np, nd orbitals for hybridisation
to yield a set of equivalent orbitals of definite geometry such as
octahedral, tetrahedral, square planar.