Disentangling the Noncovalent Interactions That Drive Coinage Metal Cluster Dimerization.

Understanding the atomistic interactions that drive self-assembly is a fundamental topic of broad interest in the design of supramolecular materials. The involvement of transition metal centers substantially enhances the number and types of interactions available in synthesizing designer chemical aggregates. In this work, we experimentally isolate supramolecular dimeric clusters of tetranuclear coinage metal (Cu, Ag, Au) monomers in the solid-state that adopt a cofacial [M4]-[M4] arrangement and exhibit short metal-metal distances and close M···H-C contacts. Through quantum chemical investigations, including atoms-in-molecules (AIM), noncovalent interaction (NCI), and local energy decomposition (LED) analysis, along with proton NMR chemical shift calculations, we establish the existence of anagostic (and metallophilic) interactions that increase in strength going from Cu to Ag to Au. We proceeded to quantify the relative contributions of various interactions to the observed dimerization. We find that multiple individually weak but cumulatively significant noncovalent interactions drive dimerization, with interligand dispersion the most prominent (24-34 kcal/mol), followed by hydrogen bonding; metallophilic and anagostic interactions contribute 2-9 and 2-6 kcal/mol, respectively. Taken together, we establish that myriad noncovalent interactions can synergistically guide the precise formation of strongly bound coinage metal dimers.