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 [M3(μ3-I)2] core. In agreement with the geometric characteristics of the M3 triangles, 31P NMR spectra exhibit a single peak for the [Cu3] cluster but a double-peak for the [Ag3] cluster. Preliminary optical studies by UV/Vis and emission techniques show major absorption shoulders at ∼286 nm for Cu3I2(dppm)3·I and ∼254 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.