What type of complexes do meridional and facial isomers apply to?

Meridional and facial isomers apply specifically to octahedral complexes, which are characterized by having a central metal ion surrounded by six ligands. In octahedral complexes, the arrangement of the ligands can lead to different geometric isomers based on how the ligands are positioned relative to one another.

The term "meridional" refers to a configuration where three identical ligands occupy positions along a plane that bisects the octahedron, allowing for symmetry and creating a distinct spatial arrangement. In contrast, the "facial" isomer occurs when the three identical ligands are grouped together on one face of the octahedral structure, which also provides a different spatial distribution than the meridional configuration.

These descriptors are only relevant in octahedral complexes because they involve the positioning of three of the same type of ligands among the six ligands surrounding the metal center, a scenario that is not relevant in tetrahedral, linear, or square planar complexes, where such positional distinctions do not apply. Thus, the classification of isomers as meridional or facial is specific to octahedral coordination geometry.