Q. Explain about Stereoisomerism?

Stereoisomers have the same bonds but the arrangement of atoms in space is different.  Stereoisomerism can be divided into two kinds: geometrical and optical.

Geometrical isomerism occurs when ligands can assume different positions around rigid bond\ with the metal ion. For example the compound Pt(NH₃)₂Cl₂ has a square  plana  structure   the two possible arrangements are shown in Fig.

In the cis-isomer the two ammonia molecules are next (cis) or adjacent to each other whereas in the trans-isomer the two ammonia molecules are across (Trans) to each other.

This type of isomerism is not possible for complexes with coordination number 2 (linear molecule). 3 (trigonal planar)  and 4 (tetrahedral geometry).