Metal−Metal Interactions in Heterobimetallic d⁸−d¹⁰ Complexes. Structures and Spectroscopic Investigation of [M‘M‘ ‘(<i>μ</i>-dcpm)₂(CN)₂]⁺ (M‘ = Pt, Pd; M‘ ‘ = Cu, Ag, Au) and Related Complexes by UV−vis Absorption and Resonance Raman Spectroscopy and ab Initio Calculations

X-ray structural and spectroscopic properties of a series of heterodinuclear d8−d10 metal complexes [M‘M‘ ‘(μ-dcpm)2(CN)2]+ containing d8 Pt(II), Pd(II), or Ni(II) and d10 Au(I), Ag(I), or Cu(I) ions with a dcpm bridging ligand have been studied (dcpm = bis(dicyclohexylphosphino)methane; M‘ = Pt, M‘ ‘ = Au 4, Ag 5, Cu, 6; M‘ ‘ = Au, M‘ = Pd 7, Ni 8). X-ray crystal analyses showed that the metal···metal distances in these heteronuclear metal complexes are shorter than the sum of van der Waals radii of the M‘ and M‘ ‘ atoms. The UV−vis absorption spectra of 4−6 display red-shifted intense absorption bands from the absorption spectra of the mononuclear trans-[Pt(phosphine)2(CN)2] and [M‘ ‘(phosphine)2]+ counterparts, attributable to metal−metal interactions. The resonance Raman spectra confirmed assignments of 1[ndσ*→(n + 1)pσ] electronic transitions to the absorption bands at 317 and 331 nm in 4 and 6, respectively. The results of theoretical calculations at the MP2 level reveal an attractive interaction energy curve for the skewed [trans-Pt(PH3)2(CN)2−Au(PH3)2+] dimer. The interaction energy of Pt(II)−Au(I) was calculated to be ca. 0.45 ev.