Syntheses, structures, bonding, and optical properties of trinuclear cluster iodides:: M3(μ3-I)2(μ-dppm)3•I (M = Cu, Ag), dppm = bis(diphenylphosphino)methane)

The title compounds were obtained from the reactions of copper or silver monohalides with the bidentate bis(diphenylphosphino)methane (dppm) ligand at room temperature in a mixed solvent. Single-crystal X-ray diffraction analyses indicate that both compounds crystallize in a monoclinic system but in different space groups. The structures are characterized by a trinuclear [M3I2(dppm)(3)](+) cation with a trigonal-bipyramid [M-3(mu(3)-I)(2)] core. In agreement with the geometric characteristics of the M-3 triangles, P-31 NMR spectra exhibit a single peak for the [Cu-3] cluster but a double-peak for the [Ag-3] cluster. Preliminary optical studies by UV/Vis and emission techniques show major absorption shoulders at similar to286 nm for Cu3I2(dppm)(3).I and similar to254 nm for Ag3I2(dppm)(3).I, but no luminescence in the non-degassed MeCN solution at 298 K. The structures, bonding, electronic excitations and emissions are discussed based on relativistic density functional theory calculations.