Cuprophilic interactions in luminescent copper(I) clusters with bridging bis(dicyclohexylphosphino)methane and iodide ligands: Spectroscopic and structural investigations

Polynuclear copper(I) complexes with bridging bis(dicyclohexylphosphino)methane (dcpm) and iodide ligands, [Cu-2(dcpm)(2)(CH3CN)(2)](BF4)(2) (1), [Cu-2(dcpm)(2)](BF4)(2) (2), [(CuI)(3)(dcpm)(2)] (3), [(CuI)(4)(dcpm)(2)] (4), and [(CuI)(2)(dcpm)(2)] (5) were prepared and their structures determined by X-ray crystal analysis. The shortest Cu-Cu distance found in these complexes is 2.475(1)Angstrom for 3. Powdered samples of 1, 3, 4, and 5 display intense and long-lived phosphorescence with lambda(max) at 460, 626, 590, and 456 nm and emission quantum yields of 0.26, 0.11, 0.12, and 0.56 at room temperature, respectively. In the solid state, 2 displays both a weak emission at 377 and an intense one at 474 nm with an overall emission yield 0.42. The difference in emission properties among complexes 1-5 suggests that both Cu-Cu interaction and coordination around the copper(I) center affect the excited state properties. A degassed solution of 2 in acetone gives a bright red emission with lambda(max) at 625 nm at room temperature. The difference absorption spectra of the triplet excited states of 1-5 in acetonitrile show broad absorption peaks at 340-410 and 850-870 nm.