Platinum(II) nucleobase complexes containing up to four different ligands: Syntheses and X-ray structure determinations of cis-[PtI-(1-MeC)(2)(NH3)]ClO4 and [PtI(1-MeC)(9-EtGH)(NH3)]ClO4 center dot 1.5H(2)O

A square-planar Pt(II) complex containing four different ligands, including the two model nucleobases 1-methylcytosine (1-MeC) and 9-ethylguanine (9-EtGH), has been prepared and studied by X-ray crystallography. [PtI(1-MeC)(9-EtGH)(NH3)]ClO4 . 1.5H(2)O (1) crystallizes in the monoclinic system, space group C2/c with a = 16.577(3), b = 16.638(2), c = 17.923(3) Angstrom, beta = 114.37(1)degrees, V = 4502(2) Angstrom(3), Z = 8. The two nucleobases which are platinated at N3 (1-MeC) and N7 (9-EtGH) are cis to each other and oriented in a way as to form a very weak H bond (3.39 Angstrom) between NH2(4) of 1-MeC and O(6) of 9-EtGH. The guanine ligand is trans to I-. The title compound represents one of three possible geometrical isomers of compounds having this composition. A closely related complex, cis-[PtI(1-MeC)(2)(NH3)] ClO4 (3), has likewise been isolated and X-ray structurally characterized: triclinic system, space group <P(1)over bar> with a = 10.490(4), b = 10.886(4), c = 9.529(3) Angstrom, alpha = 94.18(3), beta = 106.28(3), gamma = 106.33(3)degrees, V = 988(1) Angstrom(3), Z = 2. In 3 the two 1-MeC bases are platinated at N3 and oriented head-tail, with intramolecular H bonds of 3.22 and 2.95 Angstrom between pairs of NH2(4) and O(2) groups.