Dinuclear copper(I) complexes containing diimine and phosphine ligands: Synthesis, copper–copper separation and photophysical properties

Dinuclear copper(I) complexes with bridging bis(dicyclohexylphosphino)methane (dcpm) or bis(diphenylphosphino)methane (dppm) and 2,2′-bipyridine or 2-[N-(2-pyridyl)methyl]amino-5,7-dimethyl-1,8-naphthyridine (L), [Cu2(bpy)2(dppm)2](BF4)2 (1), [Cu2(bpy)2(dcpm)](BF4)2 (2), [Cu2(L)(dppm)](BF4)2 (3) and [Cu2(L)(dcpm)](BF4)2 (4) were prepared, and their structures were determined by X-ray crystal analysis. Two-, three-, and four-coordinate copper(I) centers are found in these complexes. Compounds 3 and 4 show close CuI⋯CuI separations of 2.664(3) and 2.674(1) Å, respectively, whereas an intramolecular copper–copper distance of 3.038 Å is found in 2 having only dcpm as an additional bridge. Powdered samples of 1, 3, and 4 display intense and long-lived phosphorescence with λmax at 533, 575, and 585 nm at room temperature, respectively. In the solid state, 2 exhibits only a weak emission at 555 nm. The time-resolved absorption and emission spectra of these complexes were investigated. The difference in the emission properties among complexes 1–4 suggests that both CuI⋯CuI distances and coordination environment of the copper(I) centers affect the excited-state properties.