Geometrical isomerism in complexes with coordination number 6
Octahedral complexes of formula [ MX2L4 ], in which the two X ligands
may be oriented cis or trans to each other, e. g., [ Co( NH3) 4Cl2) +.
Octahedral complexes of formula [ MX2A2 ], where X are unidentate ligands and A are bidentate ligand. form cis and trans isomers, e. g., [ CoC12( en) 2 ]’
In octahedral complexes of formula [ MA 3X3 ], if three donor atoms of the same ligands occupy adjacent positions at the corners of an octahedral face. it is known as facial( fae) isomer, when the positions are around the meridian of the octahedron, it is known as meridional( mer) isomer. e. g., [ Co( NH3) 3( NO2) 3 ]
( ii) Optical isomerism These are the complexes which have chiral structures. It arises when mirror images cannot be superimposed on one another. These mirror images are called enantiomers. The two forms are called dextro( d) and laevo( l) forms.
Tetrahedral complexes with formula [ M( AB) 2 ] show optical isomers and octahedral complexes( cis form) exhibit optical isomerism.