The new complexes trans-[a(2)Pt(Hpymo-N-1)(2)]X-2 (a = NH3, X = NO3 (1a); a = CH3NH2, X = NO3 (lb); a = CH3NH2, X = ClO4 (1c); Hpymo = 2-hydroxypyrimidine) have been prepared by reaction of trans-[a(2)Pt(H2O)(2)]- X-2 with 2-hydroxypyrimidine at 80 degrees C in water. Complex 1c cocrystallizes in water with 2-aminopyrimidine (ampym) through formation of complementary pairs of hydrogen bonds to give the supramolecular hexagon {trans-[(CH3NH2)(2)Pt(pymo-N-1)(Hpymo-N-1)] . Hampym}(2)(ClO4)(4) (2). Molecular recognition of ampym by 1c is responsible for a conformational change of the two hydroxypyrimidine ligands in Ic from anti (Ic) to syn and in addition for a proton transfer from a Hpymo residue to ampym against 1.5 units of pK(a) gradient. H-1 NMR concentration-dependent studies as well as NOE experiments in dmso-d(6) and dmf-h show that 2 dissociates in solution. Compound 1a reacts in NH3:H2O (1:3) with Ag-1 to give the polymeric species {trans-[(NH3)(2)Pt(mu-pymo-N-1,N-3)(2)Ag(H2O)]NO3}(n), (3). In contrast to 2, in the polymeric structure the trans-[(NH3)(2)Pt(pymo)(2)] entities adopt an anti conformation. Nevertheless, the [(H2O)Ag(pymo)(2)] residues present a syn conformation that leads to a meander-like global structure. Compounds Ib, Ic, 2, and 3 have been studied by X-ray crystallography: (Pb) triclinic space group, P (1) over bar, a = 9.300(2) Angstrom, b = 10.483(2) Angstrom, c = 11.050(2) Angstrom, alpha = 68.21(3)degrees, beta = 75.47(3)degrees, gamma = 73.83(3)degrees, Z = 2, R1 = 0.025, and wR2 = 0.062; (1c) triclinic space group, P1, a = 5.692(1) Angstrom, b = 7.758(2) Angstrom, c = 11.236(2) Angstrom, alpha = 93.12(3)degrees, beta = 92.86(3)degrees, gamma 102.58(3)degrees, Z = 2, R1 = 0.048, and wR2 = 0.119; (2) triclinic space group, P1, a 8.355(2) Angstrom, b = 11.221(2) Angstrom, c = 13.004(3) Angstrom, alpha = 86.76(3)degrees, beta = 78.62(3)degrees, gamma = 77.96(3)degrees, Z = 2, R1 = 0.033, and wR2 = 0.080; (3) monoclinic space group, C2/c, a = 5.345(1) Angstrom, b = 23.998(5) Angstrom, c 12.474(2) Angstrom, beta = 102.27(3)degrees, Z = 8, R1 = 0.041, and wR2 = 0.093.