The number of isomers possible for Pt en NO 2 2 is:

$\left[\mathrm{Pt}\left(\mathrm{en}\right){\left({\mathrm{NO}}_2\right)}_2\right]$

So, total possible isomers are $3$.

The existence of coordination compounds with the same formula but different arrangements of the ligands was crucial in the development of coordination chemistry. Two or more compounds with the same formula but different arrangements of the atoms are called isomers.