Structure and energy decomposition analysis of metal–metal bonding in [PhM–MPh] and [ClM–MCl] (M = Zn, Cd, Hg)

Abstract

The metal–metal bonding in the title compounds have been investigated with the help of energy decomposition analysis at the DFT/TZ2P level. The optimized Zn–Zn and Cd–Cd bond distances in model compounds [Ph 2M 2] (M = Zn, Cd) are slightly longer than the experimental values in [ R 2 M 2 ] [ R = C 6 H 3 - 2 , 6 - ( C 6 H 3 - 2 , 6 - Pr 2 i ) 2 ] . The calculated data show that bond dissociation energies (−BDE) for Zn–Zn bonds −53.99 kcal/mol in [Ph 2Zn 2] and −59.41 kcal/mol in [Cl 2Zn 2] are greater amongst the compounds under study. In addition, [Cl 2M 2] is found to have a bonding energy slightly larger than those in [Ph 2M 2]. The values of interaction energy, Δ E int, electrostatic interactions, Δ E elstat, and orbital interactions, Δ E orb are arranged in the following order: Zn > Hg > Cd. There are strong electrostatic attractions between metals, with Δ E elstat (−69.23 to −103.55 kcal/mol). The electrostatic attractions, Δ E elstat are always greater than the orbital interactions, Δ E orb. The M–M bonding has more than half ionic character (53–62%). The reason for the large electrostatic interactions is the anisotropic charge distribution at the metal atom. The results demonstrate clearly that the atomic partial charges cannot be taken as a measure of the electrostatic interactions between the atoms. The orbital interactions are relatively weaker in the cadmium–cadmium bond than in the mercury–mercury bond, whereas the Cd–Cd bond distances are longer than the Hg–Hg bond distances. We want to point out that the values of Δ E orb is not simply a function of the interatomic distances.