Metal-Metal Bonding in M2Cl6(H2PCH2PH2)2, M2Cl6(PH3)4 and M2Cl104- (M = Cr, Mo, W) Edge-Shared Dimer Systems

Abstract

Density functional theory is used to determine the electronic structures, geometries, and periodic trends in metal-metal bonding in the homo- and heterobimetallic d3d3 edge-shared systems M2Cl104-, M2Cl6(PH3)4, and M2-Cl6(H2PCH2PH2) 2 (M = Cr, Mo, W). The much shorter metal-metal distances in these complexes relative to M2Cl104- (M = Mo, W) are shown to arise solely from electronic differences between chlorine and phosphine donors. Due to inversion of the δand δ*orbitals, the complexes M2Cl6(PH3)4 and M2Cl6(H2PCH2PH2) 2 (M = Mo, W) are found to possess formal metal-metal double bonds. The periodic trends in metal-metal bonding in these systems are rationalized in terms of the energetic contributions of orbital overlap (ΔEovlp) and spin polarization (ΔEspe). The reduction in ΔEspe and increase in ΔEovlp on replacement of axial chlorides with phosphine both favor stronger metal-metal bonding in the phosphine-based complexes. The strong linear dependence observed between ΔEspe and ΔEovlp enables the metal-metal bonding in these systems to be predicted simply from singleion spin-polarization energies. The antiferromagnetic coupling in M2Cl6(H2PCH2PH2) 2 (M = Mo, W) and MoWCl6(H2PCH2PH2)2 is shown to be mostly due to coupling of the metal δ electrons, with a smaller contribution from the π electrons, particularly for the dimolybdenum complex. Show more