Structural motifs of Au(I)-Cu(I) N-heterocyclic carbene halide complexes

A series of Au(I)–Cu(I) N-heterocyclic carbene (NHC) halide complexes [AuCu₂(im(CH₂py)₂)₂X]²⁺ where X = Cl (1), Br (2), I (3) was prepared by refluxing [AuCu₂(im(CH₂py)₂)₂(NCCH₃)₄]³⁺ with the appropriate halide in acetonitrile. The compounds were characterized by NMR, absorption, and fluorescence spectroscopy. They feature similar solution behavior and solid-state photoemissions. The solid-state structures feature a rhomboidal [AuCu₂X]²⁺ core which is influenced by the type of halide. Compared to other Au(I)–Cu(I) NHC complexes, 1–3 comprise a new structural motif containing a bridging halide. The benzimidazolium analog of 1 was also characterized crystallographically. The structure of [AuCu₂(benzim(CH₂py)₂)₂Cl]²⁺ (4) features different coordination modes of the NHC ligands with the carbenic carbon bonded to both gold and copper and the pyridyl groups bonded to the same copper(I) ion.