Enhanced Metallophilicity in Metal-Carbene Systems: Stronger Character of Aurophilic Interactions in Solution.

Metallophilicity is an essential concept that builds upon the attraction between closed shell metal ions. We report on the [M (bisNHC) ] (M=Au , Ag ; NHC=N-heterocyclic carbene) systems, which display almost identical features in the solid state. However, in solution the Au cation exhibits a significantly higher degree of rigidity owed to the stronger character of the aurophilic interactions. Both Au and Ag cationic constructs are able to accommodate Ag ions via M-M interactions, despite their inherent Coulombic repulsion. When electrostatic repulsion between host and guest is partially diminished, M-M distances are substantially shortened. Quantum chemical calculations estimate intermetallic bond orders up to 0.2. Although at the limit of (or beyond) the van der Waals radii, metallophilic interactions are responsible for their behavior in solution.