M2L9 COMPLEXES

The electronic and geometrical structure of confacial bioctahedral complexes of the type L3MX3ML3is studied, for a variety of terminal ligands and hydride, halide, and carbonyl as representative bridging ligands. The factors which determine the dimer geometry in general and the metal-metal separation in particular are the geometrical preference of the L3MX3monomer fragment, the symmetry-conditioned opportunities for interaction offered up by the orbitals of the bridging group (very different for H-, Cl-, or CO), and direct metal-metal bonding. There are cases in this class of triply bridged complexes where metal-metal bonding is determinative, but they are a minority. Several cases point up the fact that in bridged complexes neither a short metal-metal distance by itself nor electron counting conventions are a good guide to the presence or absence of substantial direct metal-metal interaction. © 1979, American Chemical Society. All rights reserved.