The synthesis and characterization of a series of new mercury containing platinum-gold cluster compounds are reported. The compound [(PPh(3))Pt(AuPPh(3))(6)(HgNO3)](NO3)(1(NO3)) was prepared by the addition of metallic mercury to [(PPh(3))Pt(AuPPh(3))(6)](NO3)(2). Halide derivatives of 1 were prepared by reaction with halides X(-) (X = Cl, Pr, I) to give the series [(PPh(3))Pt(AuPPh(3))6(HgX)](+) (2). Metallic mercury can be displaced from 1 by reaction with CO (1 atm) giving the known carbonyl adduct [(PPh(3))(CO)Pt(AuPPh(3))(6)](2+). This reaction is reversible. The first tetrametallic derivatives of Pt-centered, gold cluster compounds [(PPh(3))Pt(AuPPh(3))(6)(HgCo(CO)(4))](+) (3), and [(PPh(3))Pt(AuPPh(3))(5)(HgCo(CO)(4))(2)](+) (4), have been prepared by reaction of NaCo(CO)(4) with 1 and [(PPh(3))Pt(AuPPh(3))(5)(HgNO3)(2)](+), respectively. Compound 1 has been characterized by single crystal X-ray diffraction. 1 crystalizes as a (C2H5)(2)O.(CH3)(2)CO solvate with the following crystal data : monoclinic P2(1)/c, a = 24.968 (7) Angstrom, b = 15.848 (9) Angstrom, c = 30.60 (1) Angstrom, beta = 92.69 (3)degrees, V = 12,093 Angstrom(3), Z = 4, and residuals R = 0.077 and R(w) = 0.071 for 7722 observed reflections and 462 variables and Mo K alpha radiation, at -100 degrees C. The PPtM(7) core of 1 has an unusual geometry that is best described as being between the limits of a Pt-centered, icosahedral fragment and a cube. Clusters are known with both of these limiting geometries and although 1 is in between, it is spheroidal in agreement with its 18-electron count.