Luminescent homodinuclear copper(I) halide complexes based on the 3,5-bis{6-(2,2′-dipyridyl)}pyrazole ligand

Two novel mixed-ligand dicopper(I) halide complexes, [{Cu(PPh3)X}2(μ-HL)] (HL = 3,5-bis{6-(2,2′-dipyridyl)}pyrazole, X = I (1); Br (2)), have been synthesized by a straightforward double-layer diffusion approach and structurally characterized by single-crystal X-ray diffraction. The multi-site HL acts as a bridging bis-bidentate chelate, assembling two Cu(PPh3)X moieties into copper(I) dimers possessing the triple-decker “organic” sandwich structure of phenyl/pyrazolyl/phenyl through π···π interactions. Complexes 1 and 2 exhibit photoluminescence in the solid state at ambient temperature, ascribed to a combination of intraligand charge transfer (ILCT) and metal-to-ligand charge transfer (MLCT) transitions. The emission of 2 is red-shifted 18 nm relative to that of 1 due to substitution of the iodides of 1 by the weaker electron-donating bromides.