Question

Fac-mer isomerism is associated with which one of the following complexes? (M=central metal)

• A. $[\text{M}{\left(\text{A}\text{A}\right)}_2]$
• B. $[\text{M}{\text{A}}_3{\text{B}}_3]$
• C. $[\text{M}{\left(\text{A}\text{A}\right)}_3]$
• D. $[\text{M}\text{A}\text{B}\text{C}\text{D}]$

Answer 1

Answer: (B)

Fac-mer isomerism is associated with $[\text{M}{\text{A}}_3{\text{B}}_3]$ type complexes. The fac isomer is also known as facial isomer or cis isomer. Three A ligands are present on one triangular face and three B ligands are present on opposite triangular face.
The mer isomer is also known as meridional isomer or trans isomer.
​