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

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 [Ph2M2] (M = Zn, Cd) are slightly longer than the experimental values in [R2M2][R=C6H3-2,6-(C6H3-2,6-Pr2i)2]. The calculated data show that bond dissociation energies (−BDE) for Zn-Zn bonds −53.99 kcal/mol in [Ph2Zn2] and −59.41 kcal/mol in [Cl2Zn2] are greater amongst the compounds under study. In addition, [Cl2M2] is found to have a bonding energy slightly larger than those in [Ph2M2]. The values of interaction energy, ΔEint, electrostatic interactions, ΔEelstat, and orbital interactions, ΔEorb are arranged in the following order: Zn > Hg > Cd. There are strong electrostatic attractions between metals, with ΔEelstat (−69.23 to −103.55 kcal/mol). The electrostatic attractions, ΔEelstat are always greater than the orbital interactions, ΔEorb. 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 ΔEorb is not simply a function of the interatomic distances.