Diplatinum(III) Complexes with Four Bridging 1-Methylcytosinato Nucleobases Derived from a Mononuclear trans-(NH3)2Pt^II Complex and Cu^II

A heteronuclear complex of composition trans-[(NH3)2Pt(N4-1-MeC^- -N3)2Cu(H2O)2](ClO4)2 (1a), with 1-MeC^- = 1-methylcytosinate, has been prepared and characterized by X-ray crystallography. 1a (Cu,Pt) is a linkage isomer of a previously described compound with the two metals inverted (Pt,Cu). The intermetallic distances are significantly different in the two types of compounds, 2.6109(9) (angstrom) in 1a, yet 2.49-2.56 (angstrom) in several forms of the linkage isomer. When heated in water in the presence of air, 1a is converted in low yield into diplatinum(III) compounds [(H3N)Pt(1-MeC^- -N3,N4)4Pt(NH3)]^2+ (2a) and [(H2O)Pt(1-MeC^- -N3,N4)4Pt (NH3)]^2+ (2b), which were crystallized as ClO4- salts. In a modified procedure a third representative of this group of diplatinum(III) compounds, [(O2N)Pt(1-MeC^- -N3,N4)4Pt]^+ (2c) was isolated. All three compounds contain the four bridging 1-MeC ligands in a head,tail,head,tail arrangement with Pt-Pt distances (2.4516(7)-2.4976(9) (angstrom)) that are the shortest ones among diplatinum(III) compounds containing nucleobases.