Facial isomerism is associated with which type of complex?

Facial isomerism occurs in octahedral complexes with formula MA3B3, where 'M' represents the metal center and 'A' and 'B' are different types of ligands. This type of isomerism arises from the arrangement of the ligands around the central metal atom, leading to distinct spatial configurations that cannot be interconverted through rotation or translation without breaking bonds.

In a complex such as MA3B3, the three identical ligands (A) can occupy one face of the octahedron, while the three other identical ligands (B) occupy the opposite face. This configuration results in two different isomers: one where all A ligands are adjacent (facial) and another where they are opposite each other (meridional). Therefore, the unique geometric arrangement of the ligands in complexes of the MA3B3 type leads to the possibility of facial isomerism.

While the other provided formulas represent different arrangements of ligands, they do not exhibit facial isomerism in the same manner. For example, MA2B2 complexes can only show geometric isomerism based on the relative positions of the A and B ligands without forming distinct facial isomers. Similarly, MA4B2