Valence-bond concepts in transition metals: metal hydride diatomic cations

Despite the recent advances in understanding bonds between transition metals (TM) and non-metal, there remain considerable uncertainties in both the concepts and the thermodynamics of organometallic complexes, severely limiting the understanding of mechanisms for various chemical transformation. In order to provide the flavor of some of the evolving concepts, we will focus here on MH^+ and examine the variations in bond orbitals, bond energies, and other quantities (from both experiment4 and theory) for the three rows of TM (Sc^+-Cu^+, Y^+-Ag^+, La^+, Hf^+-Au^+) the group 2 and group 12 systems. These trends also apply to other bonds to TM, in particular to metal-alkyP and metal-silyl bonds, and should be helpful in estimating and understanding the trends in other TM compounds as well.