FORMATION OF TRINUCLEAR COMPLEXES BY ADDITION OF MERCURY(II) HALIDES AND GOLD(I) HALIDES TO PT-2(MU-DPM)(2)(CN)(2)

Treatment of Pt-2(mu-dpm)(2)(CN)(2) (dpm is bis(diphenylphosphino)methane) with 1 equiv of mercury(II) iodide in a dichloromethane/methanol solution yields orange (NC)(2)Pt-2(mu-I)(mu-HgI)(mu-dpm)(2)CH2Cl2.1.5H(2)O, which crystallizes in the triclinic space group with a = 15.311(3) Angstrom, b = 16.132(5) Angstrom, and c = 24.911(6) Angstrom at 130 K with Z = 4. Refinement of 11040 reflections and 416 parameters gave R = 0.084 and R(w) = 0.117. There are two, nearly identical, molecules in the asymmetric unit. Each consists of a doubly bridged A-frame with [HgI](+) and I- fragments at the bridging sites. The Pt-Hg bond lengths for molecule A are 2.729(2) and 2.700(2) Angstrom and for molecule B are 2.725(2) and 2.700(2) Angstrom. The platinum-platinum bond is retained, Pt-Pt distance 2.823(2) Angstrom (molecule B, 2.819(2) Angstrom). Treatment of Pt-2(mu-dpm)(2)(CN)(2) with 1 equiv of mercury(II) bromide, under similar reaction conditions, yields (NC)(2)Pt-2(mu-Br)(mu-HgBr)(mu-dpm)(2), 5. Treatment of Pt-2(mu-dpm)(2)(CN)(2) with 1 equiv of Me(2)SAuCl in dichloromethane yields yellow (NC)(2)Pt-2(mu-AuCl)(mu-dpm)(2) CH2Cl2, 6, which crystallizes in the tetragonal space group P4(3) with a = 20.933(5) Angstrom and c = 14.381(6) Angstrom at 130 K with Z = 4. Refinement of 3473 reflections and 300 parameters gave R = 0.059 and R(w) = 0.081. The structure consists of two Pt(CN) groups spanned by two mutually perpendicular trans dpm ligands and bridged symmetrically by a AuCl fragment to form an A-frame. The Pt-Pt bond length (2.821(2) Angstrom) and Pt-Au bond lengths (2.633(2) and 2.648(2) Angstrom) are consistent with the presence of a two-electron, three-center bond between the three metal centers.