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

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 1:1 M 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.

Graphical abstractA series of luminescent complexes, [CuXPh2P(CH2)nPPh2] [X = I, n = 4 (1), 5 (2); X = Br, n = 4 (3), 5 (4)], have been synthesized and characterized. X-ray diffraction studies determined that 1 and 2 are both dinuclear structures with a Cu2I2 core, which is formed by two μ-I bridges and further supported by two μ2 diphosphine ligands. All the complexes exhibit a strong CT absorption band which has been assigned as halide-to-ligand charge transfer (XLCT) mixed with a little metal-to-ligand charge transfer (MLCT) transition, as confirmed by TD-DFT calculations. When the X atom changes from iodine to bromine, or the ligand changes from DPPP to DPPB, some blue-shift of the CT band has been observed, both in the experimental absorption spectra as well as the calculated ones.Figure optionsDownload full-size imageDownload as PowerPoint slide