Computational Characterization of Unsupported Au(I)···Ir(I) Metallophilic Interactions: Evidence for Strong Dispersive Stabilization

Unsupported metallophilic interactions remain experimentally unexplored in gold-iridium heterobimetallic complexes. To address this gap, we conducted a computational study on a series of model systems of the form [Ir(CO)X(PH₃)₂][AuR₂], where X = Cl, Br, and I and R = H, CH₃, NH₃, and PH₃, to evaluate their strength and feasibility. Optimizations were performed at the MP2/def2-TZVPP level of theory, and interaction energies at equilibrium distances were assessed through potential energy curves (PECs). To account for relativistic effects, calculations were complemented by spin-component-scaled (SCS)-MP2 within the zero-order regular approximation (ZORA). Further insight into the nature of these interactions was gained through analyses of NBO effective charges, bond orders, natural energy decomposition analysis (NEDA), and topological examination of electron density using QTAIM and IGMH frameworks. Our results revealed intermetallic distances consistent with significant noncovalent attraction, exhibiting unexpectedly high interaction energy values (20-60 kJ mol^-1). The presence of a bond critical point (BCP) along the Au(I)···Ir(I) bond path across all model systems confirms the attractive character of these interactions, which are characterized as regular closed-shell with a partial degree of electron sharing. Overall, this study underscores the potential importance of such noncovalent interactions in the rational design of unsupported gold-iridium heterobimetallic complexes with promising properties.