THEORETICAL-STUDIES OF THE 1ST-ROW AND 2ND-ROW TRANSITION-METAL DIMETHYLS AND THEIR POSITIVE-IONS

Using the modified coupled-pair functional (MCPF) method and Gaussian basis sets of better than double-ζ plus polarization quality we have determined equilibrium structures for the ground and selected low-lying excited states of the first- and second-row transition-metal dimethyls and their positive ions. For all these metals, the dimethyl insertion products are studied to elucidate trends in the bonding. We also study the electrostatically bound M+-C2H6 complexes for selected metals where this structure is more stable than the insertion product. In most of the dimethyls there is significant sd hybridization leading to a C-M-C bond angle of less than 134°. For Mn, Fe, Co, Ni, and Cu, the greater stability of the 3dn4s2 as compared with the 3d 4s atomic occupation leads to 4s4p hybridization, resulting in linear equilibrium structures. The metal-methyl binding energies are compared with the experimental data when available and with analogous calculations on the monomethyl transition-metal systems. Comparison of the first and second methyl binding energy reveals large variations, which can be explained in terms of the energy separations between the atomic states and the loss of atomic d-d exchange. © 1990 American Chemical Society.