Relevance of Orbital Interactions and Pauli Repulsion in the Metal–Metal Bond of Coinage Metals

The importance of relativity and dispersion in metallophilicity has been discussed in numerous studies. The existence of hybridization in the bonding between closed shell d10-d10 metal atoms has also been speculated, but the presence of attractive MO interaction in the metal-metal bond is still a matter of an ongoing debate. In this comparative study, a quantitative molecular orbital analysis and energy decomposition is carried out on the metallophilic interaction in atomic dimers (M+···M+) and molecular perpendicular [H3P-M-X]2 (where M = Cu, Ag, and Au; X = F, Cl, Br, and I). Our computational studies prove that besides the commonly accepted dispersive interactions, orbital interactions and Pauli repulsion also play a crucial role in the strength and length of the metal-metal bond. Although for M+···M+ the orbital interaction is larger than the Pauli repulsion, leading to a net attractive MO interaction, the bonding mechanism in perpendicular [H3P-M-X] dimers is different due to the larger separation between the donor and acceptor orbitals. Thus, Pauli repulsion is much larger, and two-orbital, four-electron repulsion is dominant.