The Metallophilicity Phenomenon: The Interplay of Steric, Orbital, Dispersion, and Electronic Correlation Effects in Closed-Shell Metal-Metal Contacts.

Metallophilic interactions between closed-shell metal centers play a decisive role in the structure, stability, and functional properties of multimetallic systems, yet their physical origin remains controversial. Herein, we present a systematic theoretical study of metal-metal interactions in homo- and heterobimetallic complexes, including [MCl(PH3)]2 (M = Au, Ag, Cu), [HgCl2][MCl(PH3)] (M = Au, Ag), and [PdCl2(PH3)2][MCl(PH3)] (M = Au, Ag). Correlated wave function methods (MP2 and SCS-MP2), together with a broad set of dispersion with density functional approaches, were employed to evaluate equilibrium geometries, interaction energies, and the reliability of commonly used computational models. Energy Decomposition Analysis shows that metallophilicity originates from the compensation of a repulsive steric term (electrostatic and Pauli repulsion) by stabilizing correlation/dispersion, electrostatic, and orbital contributions. Coin metal-containing complexes display enhanced orbital stabilization and weak covalent character, while Pd- and Hg-containing systems depend more strongly on correlation-driven attraction. Although dispersion with DFT methods reproduces the main qualitative trends, significant functional dependence is observed in the balance of Pauli and orbital terms. These results reconcile previous dispersion- and covalence-based interpretations within a unified framework and provide a physically transparent basis for understanding metallophilic interactions.