Different Rotamer States of Cytosine Nucleobases in Heteronuclear PtPd-, PtPd2, and Pt2Pd2Ag Complexes Derived from [Pt(2,2′-bpy)(1-MeC-N3)2]2+ (1-MeC = 1-Methylcytosine): First Examples of Species with Head–Head Oriented 1-MeC– Ligands

[Pt(2,2′-bpy)(1-MeC-N3)2](NO3)2 (1) (2,2′-bpy = 2,2′-bipyridine; 1-MeC = 1-methylcytosine) exists in water in an equilibrium of head–tail and head–head rotamers, with the former exceeding the latter by a factor of ca. 20 at room temperature. Nevertheless, 1 reacts with (en)PdII (en = ethylenediamine) to give preferentially the dinuclear complex [Pt(2,2′-bpy)(1-MeC–-N3,N4)2Pd(en)](NO3)2·5H2O (2) with head–head arranged 1-methylctosinato (1-MeC–) ligands and Pd being coordinated to two exocyclic N4H– positions. Addition of AgNO3 to a solution of 2 leads to formation of a pentanuclear chain compound [{Pt(2,2′-bpy)(1-MeC–)2Pd(en)}2Ag](NO3)5·14H2O (5) in which Ag+ cross-links two cations of 2 via the four available O2 sites of the 1-MeC– ligands. 2 and 5 appear to be the first X-ray structurally characterized examples of di- and multinuclear complexes derived from a PtII species with two cis-positioned cytosinato ligands adopting a head–head arrangement. (tmeda)PdII (tmeda = N,N,N′,N′-tetramethylethylenediamin...