Reactions of cis-[PtCl(L-<(N7)under bar>)(NH3)(2)]Cl (L = 9-ethylguanine, 9-EtGH, or 9-methyladenine, 9-MeA) with excess KI leads in slightly acidic solution to trans-PtI2(L)(NH3). Partial or complete substitution of the iodo ligands by aqua, chloro, or nucleobase ligands can be achieved and gives a series of neutral or cationic complexes. Among others, tris(nucleobase) complexes containing three different nucleobases (9-EtGH, 9-MeA, and 1-methylcytosine, 1-MeC), [Pt(1-MeC)(9-EtGH) (9-MeA)(NH3)](2+) with SP-4-3 and SP-4-4 configuration numbers have been prepared and the deprotonated form SP-4-4- [Pt(1-MeC-<(N3)under bar>)(9-EtG-<(N7)under bar>)(9-MeA-<(N7)under bar>)(NH3)]NO3. 2H(2)O (7b) has been X-ray structurally characterized : monoclinic system, space group C2/c, a = 23.817(5) Angstrom, b = 10.992(2) Angstrom, c = 21.647-(4) Angstrom, beta = 112.07(3)degrees, V = 5251.9 Angstrom(3), Z = 8. Moreover, the X-ray crystal structure analyses of trans-PtCl2-(9-EtGH-<(N7)under bar>)(NH3). 0.5H(2)O (4) and trans-[Pt(1-MeC-<(N3)under bar>)(2)(9-EtG-<(N7)under bar>)(NH3)]NO3. 3H(2)O (6b) are reported. 4 : triclinic system, space group P (1) over bar (No. 2). a = 11.557(3) Angstrom, b = 12.742(2) Angstrom, c = 8.880(2) Angstrom, alpha = 96.95(1)degrees, beta = 94.91(2)degrees, gamma = 88.32(2)degrees, V = 1293.1(5) Angstrom(3), Z = 4. 6b : triclinic system, space group Pi (No. 2), a = 10.957(2) Angstrom, b = 11.022(2) Angstrom, c = 12.916(2) Angstrom, alpha = 81.18(3)degrees, beta = 89.93(3)degrees, gamma = 64.22(3)degrees, V = 1384.2(5) Angstrom(3), Z = 2. Relative orientations of the nucleobases in these compounds appear to be dictated by intranucleobase H bond formation.