Six coordination isomers are possible for [Co(NH3)6]3+[Cr(NO2)6]3+ (excluding the given structure of molecule).
They are as shown below.
[Co(NH3)5(NO2)1]3+[Cr(NH3)1(NO2)5]3+
[Co(NH3)4(NO2)2]3+[Cr(NH3)2(NO2)4]3+
[Co(NH3)3(NO2)3]3+[Cr(NH3)3(NO2)3]3+
[Co(NH3)2(NO2)4]3+[Cr(NH3)4(NO2)2]3+
[Co(NH3)1(NO2)5]3+[Cr(NH3)5(NO2)1]3+
[Co(NO2)6]3+[Cr(NH3)6]3+