The formation of the mononuclear Pt(II) compound[Pt(NH3)(2)(Hmtpo-N-3)(2)](NO3)(2).2H(2)O (1) (Hmpto = 4,7-dihydro-5-methyl-7-oxo[1,2,4]triazolo[1,5-alpha]pyrimidine) upon reaction of Hmtpo with cisplatin is reported. Subsequent reactions of 1 with Pd(II) electrophiles of the type [Pd(am)(2)(H2O)(2)](NO3)(2) ((am)(2) = en, bpy) in neutral aqueous media afford heterobinuclear complexes of formula [(NH3)(2)Pt(mu-mtpo-N-3,N-4)(2)Pd(am)(2)](NO3)(2), where (am)(2) = bpy and en (3). On the other hand, reaction of 1 with platinum electrophile [Pt(bpy)-(H2O)(2)](2+) yields the binuclear compound [(mtpo-N-3)(NH3)(2)Pt(mu-mtpo-N-3,N-4)Pt(bpy)(OH)](NO3).6H(2)O (4). The compounds have been structurally characterized by 1-D and 2-D H-1 NMR spectroscopy and X-ray crystallography (1, 2, and 4). Compound 1 crystallizes in the triclinic space group P(1)over-bar with cell dimensions a = 7.859(1) angstrom, b = 11.811(2) angstrom, c = 12.986(2) angstrom, alpha = 73.69(1)-degrees, beta = 84.53(1)-degrees, gamma = 85.80(1)-degrees, and Z = 2. Compound 2 crystallizes in the monoclinic space group P2(1)/c with unit cell dimensions a = 13.752(1) angstrom, b = 12.5658(8) angstrom, c = 19.215(1) angstrom, beta = 118.08(1)-degrees, and Z = 4. Compound 4 crystallizes in the triclinic space group P(1)over-bar with cell unit dimensions a = 10.282(2) angstrom, b = 14.133(3) angstrom, c = 14.794(3) angstrom, alpha = 110.63(3)-degrees, beta = 97.83(3)-degrees, gamma = 108.48(3)-degrees, and Z = 2. The structure of 1 consists of mononuclear cis-[Pt(NH3)(2)(Hmtpo-N-3)(2)](2+) cations, in which the Hmtpo ligands are coordinated through N(3) in a monodentate fashion. In compound 2, two mtpo moieties bridge the metal centers through N(3) and N(4), giving rise to a Pt-Pd separation of 3.083(1) angstrom. On the other hand, only one bridging mtpo moiety is present in 4, which accounts for a lengthening in the M-M separation to 3.337(1) angstrom. The environment around the metal centers consists of four nitrogens, except for one Pt nucleus in compound 4, which presents a rare example of a terminal OH group. The H-1 NMR studies show clearly that these structures are retained in solution. Finally, a bidentate bridging mode through N(1)/N(3) is postulated for the species generated in solution by the reaction of 1 with the electrophile [Pt(NH3)(2)(H2O)(2)](2+), which may lead to tetranuclear or polymeric species.