[Cr(H O) Cl]Cl .H O a pale green colour compound and gives two chloride ions in solution and, [Cr(H O) Cl ]Cl.2H O dark green colour compound and gives one chloride ion in solution . . Stereoisomers: Similar to organic compounds, coordination compounds also exhibit stereoisomerism. The stereoisomers of a coordination compound have the same chemical formula and connectivity between the central metal atom and the ligands.
But they differ in the spatial arrangement of ligands in three dimensional space. They can be further classified as geometrical isomers and optical isomers. Geometrical isomers: Geometrical isomerism exists in heteroleptic complexes due to different possible three dimensional spatial arrangements of the ligands around the central metal atom. This type of isomerism exists in square planar and octahedral complexes.
In square planar complexes of the form [MA B ] n± and [MA BC] n± (where A, B and C are mono dentate ligands and M is the central metal ion/atom), Similar groups (A or B) present either on same side or on the opposite side of the central metal atom (M) give rise to two different geometrical isomers, and they are called, cis and trans isomers respectively. The square planar complex of the type [M(xy) ] n± where xy is a bidentate ligand with two different coordinating atoms also shows cis-trans isomerism. Square planar complex of the form [MABCD] n± also shows geometrical isomerism. In this case, by considering any one of the ligands (A, B, C or D) as a reference, the rest of the ligands can be arranged in three different ways leading to three geometrical isomers.
XII U5 Coordination XII U5 Coordination - - - - Figure . MA B , MA BC, M(xy) & MABCD - isomers Type Example Cis Isomer Trans isomer MA B Cl NH H N Cl Pt + Cl NH H N Cl Pt + MA BC Br NH H N Cl Pt + NH