1,3-Dimethyluracil (1,3-DimeU) reacts with trans-[(CH3NH2)(2)Pt(H2O)(2)](+) to give trans-[(CH3NH2)(2)Pt(1,3-DimeU-C-5)(H2O)]X (X = NO3-, 1a, ClO4-, 1b) and subsequently with NaCl to give trans-(CH3NH2)(2)Pt(1,3-DimeU-C5)Cl (2) or with NH3 to yield trans-[(CH3NH2)(2)Pt(1,3-DimeU-C5)(NH3)]Cl (3). In a similar way, (dien)Pt-II forms [dienPt(1,3-DimeU-C5)](+) (4). Reactions leading to formation of 1 and 4 are slow, taking days. In contrast, Hg(CH3COO)(2) reacts fast with 1,3-DimeU to give (1,3-DimeU-C5)Hg(CH3COO) (5). Both 1-methyluracil(1-lMeUH) and uridine (urdH) react with (dien)Pt-II initially at N(3) and subsequently with either (dien)Pt-II or Hg(CH3COO)(2) also at C(5) to give the diplatinated species 7 and 9 or the mixed PtHg complex 8. C(5) binding of either Pt-II or Hg-II is evident from coupling of uracil-H(6) with either Pt-195 or Hg-199 nuclei and (3)J values of 47-74 Hz (for Pt compounds) and 185-197 Hz (for Hg compounds). J values of Pt compounds are influenced both by the ligands trans to the uracil C(5) position and by the number of metal entities bound to a uracil ring. Both 2 and 5 were X-ray structurally characterized. 2 : monoclinic system, space group P2(1)/c, a (6) Angstrom, c = 25.655 (10) Angstrom, beta = 145.55(3)degrees, V = 2621.9(28) Angstrom(3), Z = 4. 5 : monoclinic system, space group P2(1)/c, a = 4.905(2) Angstrom, b = 18.451(6) Angstrom, c = 11.801(5) Angstrom, beta = 94.47(3)degrees, V = 1064.77(72) Angstrom(3), Z = 4.