Optical Isomerism in coordinate complex

What is optical isomerism?

It is a type of stereoisomerism in which the isomer molecules have the tendency to rotate plan of polarized light and also show chiral behaviour. These compounds are called as Optically active compounds.

Condition required for optical isomerism:

• The molecule should be disymmetrical means they should not contain; a plane of symmetry which divides the molecule in two equal halves.

• Presence of a chiral molecule which makes a non superimposable mirror images of the compound. (A Chiral molecule is that in which a carbon is attached with four different groups.)

• The isomers should have non superimposable mirror images, and these images are called the enentiomers.

Coordinate complex that show optical isomerism:

1) Four Coordination Compound:

• Optical isomers are possible for tetrahedral complex but not for square planar complex.

• Optical isomerism is shown by tedrahedral complexes of type [Mabcd]  where central metal (M) is attached to four different monodentate ligands (a, b, c and d).

• The tetrahedral complexes of Be(II), Zn(II)and B(III) which contain unsymmetrical bidendate ligands also show optical isomerism.

  

2) Six Coordination Compound:

• The octahedral complexes of the type [Ma₂b₂c₂], [Ma₂b₂cd], [Ma₂bcde] and [Mabcdef] are optically active where a,b,c,d,e and f are monodendate ligands.

• The octahedral complexes of the type [M(A-A) ₃]^+_n show optical isomerism where (AA) is a symmetrical bidendate ligand.

• Complexes of the type [M(A-A) ₂X₂] also show optical isomerism where(AA) is symmetrical bidentate ligand whereas X is monodentate ligand. The cis form of this type of complex is optically active whereas trans form is optically inactive.

• Similarly the cis form of the complex [M(A-A) ₂BC]^+-n is optically active.

• Complexes of the type [M(A-A)B₂C₂] also show optical isomerism.

• Complexes containing optically active ligands show optical isomerism. Example:[Co(en)₂(pn) ₂ (NO₂)₂]⁺ and the complexes containing polydendate ligands also show optical isomerism. Example:[Co(EDTA)]^-