Metal-metal interactions in dinuclear d8 metal cyanide complexes supported by phosphine ligands.: Spectroscopic properties and ab initio calculations of [M2(μ-diphosphine)2(CN)4] and trans-[M(phosphine)2(CN)2] (M=Pt, Ni)

Structural, spectroscopic properties on the dinuclear [M-2(dcpm)(2)(CN)(4)] (M = Pt, 1a; Ni, 2a, dcpm = bis(dicyclohexylphosphino)methane) and [M-2(dmpm)(2)(CN)(4)] (M = Pt, 1b; Ni, 2b, dmpm = bis(dimethylphosphino)methane) and the mononuclear trans-[M(PCy3)(2)(CN)(2)] (M = Pt, 3; Ni, 4, PCy3 = tricyclohexylphosphine) and theoretical investigations on the corresponding model compounds are described. X-ray structural analyses reveal (PtPt)-Pt-... and (NiNi)-Ni-... distances of 3.0565(4)/3.189(1) Angstrom and 2.957(1)/3.209(8) Angstrom for 1a/1b and 2a/2b, respectively. The UV-vis absorption bands at 337 nm (epsilon 2.41 x 10(4) dm(3) mol(-1) cm(-1)) for 1a and 328 nm (epsilon 2.43 x 10(4) dm(3) mol(-1) cm(-1)) for 1b in CH2Cl2 are assigned to (1)(5d(sigma)(*) --> 6p(sigma)) electronic transitions originating from Pt(II)-Pt(II) interactions. Resonance Raman spectroscopy of 1a, in which all the Raman intensity appears in the Pt-Pt stretch fundamental (93 cm(-1)) and overtone bands, verifies this metal-metal interaction. Complexes 1a and 1b exhibit photoluminescence in the solid state and solution. For the dinuclear nickel(II) complexes 2a and 2b, neither spectroscopic data nor theoretical calculation suggests the presence of Ni(II)-Ni(II) interactions. The intense absorption bands at lambda > 320 nm in the UV-vis spectra of 2a and 2b are tentatively assigned to d --> d transitions.