Luminescent dinuclear copper(I) halide complexes double bridged by diphosphine ligands: Synthesis, structure characterization, properties and TD-DFT calculations

Abstract

Four luminescent copper(I) halide complexes of the type [CuXPh2P(CH2)nPPh2] [X=I, n=4 (1), 5 (2); X=Br, n=4 (3), 5 (4)] were prepared by reacting CuX with the appropriate diphosphine in a 1:1M ratio. All the complexes were characterized by spectroscopic analysis (IR, UV–Vis), elemental analysis and photoluminescence studies. Single-crystal X-ray diffraction revealed that 1 and 2 are both dinuclear structures which are constructed by two μ-I bridges and, especially, two diphosphine ligands as μ2 bridges. The copper(I) iodide complexes are thermally stable, and 2 melts at 242°C. All the complexes exhibit a strong emission in the solid state. The excited states have been assigned as a halide-to-ligand charge transfer (XLCT) state mixed with a small amount of a metal-to-ligand charge transfer (MLCT) transition, based on the TD-DFT calculations. The calculated electronic transitions have also been compared with the experimental absorption spectra to understand the reason why there is some blue-shift of the low-energy band when the halide atom changes from iodine to bromine, and an even greater blue-shift when the ligand changes from DPPP to DPPB.