Dipyridylamine-Functionalized N-Heterocyclic Carbene Ligands for Structurally Diverse Silver(I) and Gold(I) Complexes: Topology, Metallophilic Interactions, and Structure–Property Relationships

Abstract Macrocyclic N-heterocyclic carbene (NHC) ligands incorporating multidentate donor motifs offer opportunities for constructing structurally diverse coordination complexes. Herein we report a family of dipyridylamine (DPA)-functionalized NHC ligands comprising acyclic ([H2L1](PF6)2) and macrocyclic architectures ([H4L2](OTf)4 and [H4L3](OTf)4) with distinct coordination topologies. Structural studies reveal linker-dependent ligand conformations ranging from Z-shaped and double-V structures to folded and extended macrocycles, enabling tunable cavity sizes and coordination environments. Metalation with Ag(I) and Au(I) affords mono-, di-, and trinuclear complexes. The trinuclear silver complex [(AgL1)2Ag](PF6)3 and heterometallic complex [(AuL1)2Ag](PF6) feature short metal–metal separations consistent with metallophilic interactions. In solution, DOSY NMR and mass spectrometry identify [AgL1]+ and [AuL1]+ as the predominant species, suggesting dissociation of the trinuclear assemblies. Variable-temperature NMR and thermodynamic analyses reveal comparable exchange dynamics for the ethylene-linked [Ag2L2](OTf)2 and [Au2L2](OTf)2. Selected complexes exhibit enhanced solid-state luminescence arising from cooperative π–π stacking and metallophilic interactions, whereas antibacterial studies reveal enhanced activity upon metal coordination, with the Ag(I) complexes showing pronounced activity toward Escherichia coli (E. coli) and the Au(I) complexes exhibiting greater solution stability and broader antibacterial activity. These results establish DPA-functionalized NHC ligands as versatile platforms for coinage-metal assemblies with tunable topology, metal–metal interactions, photophysical properties, and biological activity.