Trends in back-bonding in the series trans-[M(C = CR)Cl(PH3)(4)] (M = Fe, Ru, Os; R = H, Ph, C6H4NO2-4)

The electronic structure of the complexes trans-[M(C=CR)Cl(PH3)(4)] (M = Fe , Ru, Os; R = R, Ph, C6H4NO2-4) has been investigated using approximate den sity functional theory in order to examine the M-C back-bonding interaction . For all three metal systems, the pi back-bonding increases in the order R = H < Ph < C6H4-4-NO2, indicating that the pi acceptor character of the ac etylide ligand increases with the electron-withdrawing ability of the subst ituent. The inclusion of relativistic effects in the calculations results i n a metal dependence of Fe similar to Ru < Os for the back-bonding, consist ent with the observed trend in quadratic hyperpolarizabilities, beta. (C) 2 000 Published by Elsevier Science S.A. All rights reserved.