Diplatinum(III) Complexes with Four Bridging 1-Methylcytosinato Nucleobases Derived from a Mononucleartrans-(NH3)2PtIIComplex and CuII

Abstract

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) Å in 1a, yet 2.49−2.56 Å 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) Å) that are the shortest ones among diplatinum(III) compounds containing nucleobases.