Nonoctahedral structures

There is always a special reason when six-coordinate molecules or complexes are nonoctahedral. The Jahn-Teller distortion is the longest known example. Also well understood now is the steric activity or nonactivity of a nonbonding electron pair, for example XeF6. In the past few years, it became obvious that six-coordinate d(0) and d(1) complexes with sigma only ligands such as Mo(CH3)(6) are far from octahedral; rather, they are trigonal prismatic or even C-3nu, distorted trigonal prismatic. This phenomenon can be explained with simple molecular orbital or valence bond models.