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 .