Further considerations on the structure and bonding in edge-sharing bioctahedral complexes

Rinaldo Poli (1) , Raymund Torralba (1)

1 University of Maryland [College Park]

Extended Huckel MO calculations have been carried out on model compounds that mimic transition metal edge-sharing bioctahedral (ESBO) complexes of stoichiometry M2X6L4 (X=anionic ligand with lone pairs for bridge-bonding and for π bonding, L=neutral 2-electron donor ligand), and for the corresponding mononuclear cis-MX4L2 system. The widening of the cis-Leq-M-Leq angle (eq=equatorial) is shown to cause the narrowing of the opposite X-M-X angle which, for the ESBO complexes, disfavors the formation of a strong metal-metal interaction. The calculations also address the importance of the M-X π interactions in metal-metal bonded dimers. The Xax (ax=axial) ligands are shown to be better π donors than the Xeq ligands for the configurations d1-d1 through d5-d5, the differential between the π donating abilities in the two different positions being maximal for the d1-d1 configuration. This effect is proposed to be responsible for the preference of d1-d1 systems for the ESBO structure having all L ligands in equatorial positions, whereas the metal-metal bonded ESBO compounds of all other electronic configurations as well as all non-bonded ESBO complexes prefer the structure with two Leq on one metal and two Lax, on the other one on steric grounds. The MO model presented here is also in excellent agreement with the observed trends of M-Clax, M-Cleq and M-Clbr (br=bridging) bond distances as a function of dnd-n configuration.

Domaines: Chimie de coordination; Chimie théorique et/ou physique

Rinaldo Poli, Raymund Torralba. Further considerations on the structure and bonding in edge-sharing bioctahedral complexes. Inorganica Chimica Acta, 1993, 212 (1-2), pp.123-134. ⟨10.1016/S0020-1693(00)92317-X⟩. ⟨hal-03533347⟩