Binuclear organometallic compounds containing planar tetra co-ordinated carbon atoms: theoretical study on geometrical and bonding patterns

Structure and bonding in the binuclear complex 1, the metallacyclocumulene, 2 and the metal-acetylene complex, 3, are studied using Density Functional Theory. The C-C bond lengths in metal-acetylene complex mainly depend on the diffuseness of the orbitals of the metal atom. Since the C1-C2-C3 angle in 2 changes to give effective overlap as the size of the metal is changed, the central C-C bond length of the cumulene remains nearly constant. In many ways the ML2 fragments determine that the bond angles C1-C2-C3 and C4-C3-C2 and the distance C2-C3 to have effective overlap with the C4H2 frame. Four in-plane delocalized molecular orbitals and two pi molecular orbitals perpendicular to the MC4M' plane contribute to the stability of the planar tetra coordination around the two central carbon atoms. At the B3LYP/LANL2DZ levels, the stability of the complex, 1, increases with decrease in the size of the M'.