Synthesis, characterization, and luminescence properties of mononuclear copper(I) halide complexes of 2-(2-benzimidazolyl)-6-methylpyridine

Three new mononuclear copper(I) halide complexes of 2-(2-benzimidazoly)-6-methylpyridine (Hbmp), [Cu(Hbmp)(PPh3)X] (X = I (1); Br (2); Cl (3)), have been synthesized and structurally characterized by X-ray crystallography. It is revealed that the most significant impact of the auxiliary halide ligand on the structure is on the Cusingle bondNpyridyl and Cusingle bondP bond lengths. Complexes 1–3 show a weak low-energy absorption band at 350–600 nm in CH2Cl2, ascribed to the Cu(I) to Hbmp metal-to-ligand charge-transfer (MLCT) transitions, perhaps mixed with some halide-to-ligand charge-transfer (XLCT) character. The solid-state emissions of 1–3 are observed at ambient temperature, markedly depending on the halide ancillary ligand bound to the {Cu(Hbmp)(PPh3)} unit, which are assigned to the MLCT excited states with some mixing of the XLCT characters.