Question

Which of the following can show face-mer isomerism?

• A. Co(en)$_2$Cl$_2$
• B. [Co(NH$_3$)$_4$Cl]$_2$
• C. [Co(H$_2$O)$_6$]$_1$X
• D. [Co(NH$_3$)$_3$Cl$_3$]

Hint:

Face-mer isomerism occurs in octahedral complexes where three identical ligands can be arranged either on the same face (fac) or in a meridional arrangement (mer). To check for possible face-mer isomerism, ensure there are at least two identical ligands in the coordination sphere.

Answer 1

The Correct Option is A

Face-mer isomerism is a type of isomerism found in octahedral coordination compounds that contain two or more identical ligands. Face-mer isomerism occurs when three identical ligands occupy positions in the same face of the octahedron (mer) or on adjacent faces (fac). - Option (a) Co(en)$_2$Cl$_2$: This complex can show face-mer isomerism because the ethylenediamine (en) ligands can be arranged in such a way that they form either a facial (fac) or meridional (mer) isomer. - Option (b) [Co(NH$_3$)$_4$Cl]$_2$: This is not a valid complex for face-mer isomerism because it has too many NH$_3$ ligands and only one chloride, making face-mer isomerism impossible. - Option (c) [Co(H$_2$O)$_6$]$_1$X: This compound also does not show face-mer isomerism as it doesn't have the necessary number of identical ligands to form either type of isomer. - Option (d) [Co(NH$_3$)$_3$Cl$_3$]: This complex cannot exhibit face-mer isomerism because all three NH$_3$ and three chloride ligands are identical in number and cannot form distinct face-mer isomers. Thus, option (a) is the correct answer.