OPTICAL ISOMERISM: This isomerism arises when a compound can be represented by two asymmetrical structures called optical isomers.
The two isomers are structurally the mirror images of each other and non-super imposable and donot possess the plane of symmetry. Optical isomerism is common in octahedral complexes involving 2 or 3 symmetrical bidentate groups of the type MAA2X2, and M AA3 and M AA B2X2. Ex: Cis-dichloro bis ethylenediamine Cobalt 3 Cis-form is optically active d and l forms where as trans- form is optically inactive due to plane of symmetry. M AA3 – tris ethylenediamine chromium 3 ion trioxaloto chromate 3 ion. 3 diammine dichloro ehylenediamine cobalt 3 ion Complexes containing hexadentate ligand EDTA show optical activity Eg: Co EDTA ethylene diamine tetra aceto cobaltate 3 ion Complex of the type [MABCEDF] type also exhibit iptical isomersm. The optical activity has been observed for chelated tetrahedral and square planar complexes but only rarely. In tetrahedral complexes only the type which occur in bis chelates with unsymmetrical ligand has been detected. These have been found in Be 2 ,B 3,Zn 2 and Cu 2 complexes. Ex: 1 bis salicylaldehyde boron 3 cation has been found to be racemic and resolution has been accomplished. The two enantiomers of bis benzoylacetonato beryllium 2. Square planar complexes are seldom optically active. Bonding in coordination compounds: The formation of coordination compounds can be explained electronically by the number of theories like I Valence bond theory: This was given by Linus pauling. In this approach, the basic assumption made is that the metal ligand bonds arise by way of donation of pairs of electron from ligands to the metal. i.e., through forming the coordinate covalent bond. In order to accomidate these electrons the metal ion must posses Requisite number of vacant orbital’s of similar energy.

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