Elucidation of coordination geometries and intermetallic interactions in electronically modified NHC complexes of group 10 and 11

The synthesis and characterization of group 10 (Ni^II, Pd^II, Pt^II) and group 11 (Cu^I, Ag^I, Au^I, Au^III) N–heterocyclic carbene (NHC) complexes supported by a methyl–substituted macrocyclic ligand is reported. NMR, ESI–MS, elemental analysis, and single–crystal X–ray diffraction (SC–XRD) confirm their structure. The d⁸ metals adopt square–planar geometries, with M–C bond lengths increasing from Ni to Pt and reduced backbone distortion. The d¹⁰ series forms tetranuclear Cu₄L₂, Ag₄L₂, and Au₄L₂ species featuring cuprophilic, argentophilic, and aurophilic interactions stabilized by the rigid macrocyclic scaffold. Comparative analysis reveals that methyl substitution enhances σ–donor character at the carbene center, promoting close metal–metal contacts. Hirshfeld surface and void analyses further confirm that crystal packing is dominated by H⋯H and C–H⋯F contacts, with minimal π–π stacking or intermolecular metallophilic interactions, and that packing efficiency varies from nearly space–filling (Ni3-OTf, Pd3-OTf, Pt3-OTf) to more open frameworks (Ag₄(3)₂-PF₆, Au₄(3)₂-PF₆). These structural and electronic insights underline the potential of macrocyclic NHCs for future applications.