Synthesis, structural and spectroscopic characterization of mono- and binuclear copper(I) complexes with substituted diimine and phosphine ligands

The reaction of [Cu(CH3CN)4]BF4, 6-(4-methoxyl)phenyl-2,2′-bipyridine (designated as MeO-CNN), and/or tricyclohexylphosphine (PCy3) and diimine ligands derived from 4,4′-bipyridine gave four mono- and binuclear copper(I) complexes, [Cu(MeO-CNN)2]BF4 (1), [Cu2(MeO-CNN)2(PCy3)2(4,4′-bipy)](BF4)2 · 1.5CH2Cl2 (2) (bipy = bipyridine), [Cu2(MeO-CNN)2(PCy3)2(bpete)](BF4)2 · 4CH2Cl2 (3) (bpete = trans-1,2-bis(4-pyridyl)ethene) and [Cu2(MeO-CNN)2(PCy3)2(4,4′-azpy)] (BF4)2 · 1.5CH2Cl2 (4) (azpy = azobispyridine). Crystallographic studies of complexes 1–4 show that each copper(I) center adopts a pseudo-tetrahedral coordination geometry. Complexes 2–4 consists of –Cu(MeO-CNN)(PCy3) units which are linked through 4,4′-bipy, bpete and 4,4′-azpy, respectively. The UV–Vis spectra of these four complexes all exhibit intense high-energy absorptions at λmax < 340 nm and broad visible bands in a range of 430–550 nm, ascribed to intraligand (IL π → π∗) transitions and metal-to-ligand charge-transfer (MLCT) transitions, respectively. The density functional theory calculation was used to interpret the absorption spectrum of 1, which further supports the assignment of MLCT character. The binuclear complexes 2 and 3 both display red solid-state emissions centred at 620 and 660 nm from metal-to-ligand charge-transfer excited state, respectively. Interestingly, the electron paramagnetic resonance (EPR) spectral measurements confirm copper(I) complexes oxidized to corresponding copper(II)–halide product upon excitation at 355 nm in dichloromethane solution.

Graphical abstractSynthesis, structural characterization, and photophysical properties of a series of new mono/binuclear copper(I) complexes with substituted 2,2′-bipyridine, tricyclohexylphosphine and 4,4′-bipyridine derivatives are processed. EPR spectral measurements confirm the copper(I) complex oxidized to corresponding copper(II)–halide product upon excitation at 355 nm in dichloromethane solution.Figure optionsDownload full-size imageDownload as PowerPoint slide