Covalent or not? Energy decomposition analysis of metal–metal bonding in alkaline-Earth dimetallocene complexes

Abstract

The geometries, metal–metal bond dissociation energies of Group 2 dimetallocene complexes M 2( η 5–C 5H 5) 2 (M = Be, Mg, Ca, Sr and Ba) have been calculated using density functional theory at the BP86 level with TZ2P basis sets. The nature of metal–metal bonding has been analyzed with an energy decomposition method. The results revealed that the M–M binding interactions in these nonpolar bonding alkaline-Earth metal complexes have more ionic character than covalent character, rather than the sole covalent bond. Molecular orbital calculations indicate that, for the heavier alkaline-Earth metal (Ca, Sr and Ba) compounds, substantial ( n − 1) d character is found in the δ bonding between metal and cyclopentadiene (Cp) ring, while there is few δ bonding interaction between M–M bond due to longer M–M bond distance.