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 metall ic 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 h ave been characterized by spectroscopic and analytical methods, and th e 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), orthor hombic 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 fo r 7504 observed reflections and 441 variables, Mo k alpha radiation. T he structure of the cluster con of 2(NO3)(2) is a Pd centered square-a ntiprism with bare Hg atoms capping the two square faces. A crystal of the Pt analog, 1(NO3)(2), was isomorphous and presumably isostructura l 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 reactio ns of 1-7 with CO, Cl-, and redox agents have been examined. Important ly, 1 was quantitatively converted into its 18-electron analog 6 by th e addition of 2 equiv of Fe(eta(5)-C5H5)(2)(+), supporting its 20-elec tron description.