Chapter 21, Problem 21.12A

How many diastereoisomer are possible for the following complexes?Draw the structure of each diastereoisomer.
(a) ${\left[{\text{CoCl}}_{\text{2}}{\text{Br}}_{\text{2}}\right]}^{\text{2}-}$ (tetrahedral)  (b) $\text{Pt}\left(\text{en}\right){\text{Cl}}_{\text{2}}$ (square planar)
(c) $\text{Pt}{\left({\text{NH}}_{\text{3}}\right)}_{\text{2}}{\left(\text{SCN}\right)}_{\text{2}}$ (square planar)  (d) $\text{Co}{\left({\text{NH}}_{\text{3}}\right)}_{\text{3}}{\left({\text{NO}}_{\text{2}}\right)}_{\text{3}}$