Question

Square planar complexes of the type MAXBL (where A,B,X,L are unidentate ligands) show the following set of isomers.
a.) Two cis and one trans
b.) Two trans and one cis
c.) Two cis and two trans
d.) Three cis and one trans

Answer 1

Hint: A square planar complex having similar ligands at adjacent positions (${90^0}$) is called cis isomer while the complex with similar ligands at opposite positions (${180^0}$) is called trans isomer.

Complete step by step answer:
The complex compounds which have the same ligand in the coordination sphere but relative positions of ligands round the central metal atom are different are called geometrical isomers and the phenomenon is called geometrical isomerism. The square planar complexes with coordination number four shows cis-trans geometrical isomerism.
Unidentate ligands are those which binds through only one site.
Normally when we see cis-trans isomerism, we have two ligands same on basis of which we differentiate in cis and trans. As all four ligands are different here, we will first assume that ‘A’ and ‘B’ are similar while ‘X’ and ‘L’ are similar. Thus, on the basis of this we will draw the structure as-
             

Thus, we get three structures of which two are in cis form while one is in trans form.
Example- $\left[ {P{t^{2 + }}\left( {N{H_3}} \right)\left( {py} \right)\left( {Cl} \right)\left( {Br} \right)} \right]$ So, the correct answer is “Option A”.

Note: Geometrical isomerism can-not be shown by tetrahedral complexes because all four ligands are in adjacent positions and all the four bond angles are the same.