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 [M ₃I₂(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.