X-ray structural and spectroscopic properties of a series of heterodinuclear d(8)-d(10) metal complexes [M'M"(mu-dcpM)(2)(CN)(2)](+) containing d(8) Pt(II), Pd(II), or Ni(II) and d(10) 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)[nd(sigma)*-->(n + 1)p(sigma)] 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.