The nature of metallophilic interactions in closed-shell d8–d8 metal complexes

Abstract

We have quantum chemically analyzed the closed-shell d⁸–d⁸ metallophilic interaction in dimers of square planar [M(CO)₂X₂] complexes (M = Ni, Pd, Pt; X = Cl, Br, I) using dispersion-corrected density functional theory at ZORA-BLYP-D3(BJ)/TZ2P level of theory. Our purpose is to reveal the nature of the [X₂(CO)₂M]⋯[M(CO)₂X₂] bonding mechanism by analyzing trends upon variations in M and X. Our analyses reveal that the formation of the [M(CO)₂X₂]₂ dimers is favored by an increasingly stabilizing electrostatic interaction when the M increases in size and by more stabilizing dispersion interactions promoted by the larger X. In addition, there is an overlooked covalent component stemming from metal–metal and ligand–ligand donor–acceptor interactions. Thus, at variance with the currently accepted picture, the d⁸–d⁸ metallophilicity is attractive, and the formation of [M(CO)₂X₂]₂ dimers is not a purely dispersion-driven phenomenon.