Metallophilicity vs Metal-Halogen Bonds: The Dominant Driving Force in Self-Assembly of Metal Clusters

Metallophilic interactions are prevalent in numerous metal clusters, where closed-shell metal centers exhibit mutual attraction even though they possess identical electrostatic properties. Generally, closed-shell metallophilicity with the combined effects of covalent bonding, Pauli repulsions, and van der Waals dispersion forces typically acts as an auxiliary interaction in stabilizing or constructing metal clusters. However, the combination between N-heterocyclic carbene-Au(I) and [CuI₂]^- is preponderantly driven by the closed-shell Cu(I)-Au(I) interactions rather than the Au-I bonds with a covalent advantage. This bonding behavior is counterintuitive, where the closed-shell metallophilicity overrides the coexisting metal-halogen bonds during self-assembly of the polymeric nanomaterials. Based on the experimental structure, we clarify that electrostatic attraction and covalent metallophilicity alternate as the dominant driving forces in the formation of the gradually lengthened closed-shell metal chain. Notably, the ionic and orbital interactions between closed-shell species can be regulated by tuning the Lewis acidity and basicity of the substituents. This study provides a novel perspective that metallophilic interactions, depending on their covalent nature, can serve as a key foundation for the precise design of functional metal clusters, while also contributing to the expansion of cluster self-assembly theory.