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Which of the following will give maximum number of isomers : -
A
$[Co(NH_3)_4Cl_2]$
B
$[Ni(en)(NH_3)_4]^{2+}$
C
$[Ni(C_2O_4)(en)_2]^{2-}$
D
$[Cr(SCN)_2(NH_3)_4]^+$
Detailed Solution
$[Co(NH_3)_4Cl_2]$: $MA_4B_2$ type, shows only cis and trans geometrical isomers (2).
$[Ni(en)(NH_3)_4]^{2+}$: the en ligand must span cis positions, so there is only one form.
$[Ni(C_2O_4)(en)_2]^{2-}$: $M(AA)(BB)_2$ type; it exists as a pair of enantiomers (d and l), i.e. 2 isomers.
$[Cr(SCN)_2(NH_3)_4]^+$: $MA_4B_2$ type gives cis and trans forms. In addition, the ambidentate SCN ligand can bind through S (thiocyanato) or N (isothiocyanato), so each SCN can be S- or N-bonded (SCN, SCN; SCN, NCS; NCS, NCS). Combining geometrical and linkage isomerism gives the largest number of isomers.
So $[Cr(SCN)_2(NH_3)_4]^+$ gives the maximum number of isomers.
$[Ni(en)(NH_3)_4]^{2+}$: the en ligand must span cis positions, so there is only one form.
$[Ni(C_2O_4)(en)_2]^{2-}$: $M(AA)(BB)_2$ type; it exists as a pair of enantiomers (d and l), i.e. 2 isomers.
$[Cr(SCN)_2(NH_3)_4]^+$: $MA_4B_2$ type gives cis and trans forms. In addition, the ambidentate SCN ligand can bind through S (thiocyanato) or N (isothiocyanato), so each SCN can be S- or N-bonded (SCN, SCN; SCN, NCS; NCS, NCS). Combining geometrical and linkage isomerism gives the largest number of isomers.
So $[Cr(SCN)_2(NH_3)_4]^+$ gives the maximum number of isomers.