ADDITION OF METALLIC MERCURY TO PLATINUM-GOLD AND PALLADIUM-GOLD CLUSTER COMPOUNDS - X-RAY CRYSTAL AND MOLECULAR-STRUCTURES OF [(HG)(2)PD(AUPPH(3))(8)](NO3)(2) AND [(HG)PT(AUPPH(3))(8)](NO3)(2)

Several new cluster compounds have been prepared by reaction of metallic Hg with the 16-electron clusters [M(AuPPh(3))(8)](n+) (M = Pt, Pd, n = 2; M = Au, n = 3) to form the 20-electron clusters [(Hg)(2)M(AuPPh(3))(8)](2+) (M = Pt, 1; Pd, 2) and [(Hg)(2)Au(AuPPh(3))(8)](3+) (3). In contrast, reaction of the 16-electron clusters with Hg-2(2+) salts gave the 18-electron clusters [(HgNO3)(2)M(AuPPh(3))(8)](2+) (M = Pt, 6; Pd, 7). The 18-electron, monomercury clusters [(Hg)M(AuPPh(3))(8)](2+) (M = Pt, 4; Pd, 5) were isolated as intermediates in the formation of clusters 1 and 2 and were also prepared by reaction of clusters 1 or 2 with 1 equiv of [M(AuPPh(3))(8)](2+) (M = Pt, Pd). Clusters 1-7 have been characterized by spectroscopic and analytical methods, and the nitrate salts of 2 and 4, by single crystal, X-ray diffraction. The crystal data for these compounds are as follows: for 2(NO3)(2), orthorhombic Fddd, a = 34.66(2) Angstrom, b = 42.09(3) Angstrom, c = 39.29(3) Angstrom, V = 57 329 Angstrom(3), Z = 16, residuals R = 0.099 and R(w) = 0.098 for 1777 observed reflections and 152 variables, Mo K alpha radiation; for 4(NO3)(2), monoclinic P2(1)/n, a = 16.95(2) Angstrom, b = 31.60(3) Angstrom, c = 25.69(3) Angstrom, beta = 93.07(7)degrees, V = 13 725 Angstrom(3), Z = 4, residuals R = 0.088 and R(w) = 0.081 for 7504 observed reflections and 441 variables, Mo k alpha radiation. The structure of the cluster con of 2(NO3)(2) is a Pd centered square-antiprism with bare Hg atoms capping the two square faces. A crystal of the Pt analog, 1(NO3)(2), was isomorphous and presumably isostructural to 2(NO3)(2). The structure of 4(NO3)(2) is similar to that of 2(NO3)(2) With one of the capping Hg atoms removed. A crystal of 5(NO3)(2) was isomorphous and presumably isostructural to 4(NO3)(2). The reactions of 1-7 with CO, Cl-, and redox agents have been examined. Importantly, 1 was quantitatively converted into its 18-electron analog 6 by the addition of 2 equiv of Fe(eta(5)-C5H5)(2)(+), supporting its 20-electron description.