CYTOSINE NUCLEOBASE AS A TRIDENTATE LIGAND - METAL-BINDING TO N(3), N(4) AND O(2) IN TRANS-[(NH(2)ME)(2)PT(DMCYT)(2)AG-2][NO3](2) (DMCYT=1,5-DIMETHYLCYTOSINATE)

1,5-Dimethylcytosine (Hdmcyt). which is a model of the naturally occurring 5-methylcytidine nucleobase, has been demonstrated to be capable of binding three metal ions simultaneously, via N(3), monodeprotonated N(4) and O(2). The compound trans-[(NH(2)Me)(2)Pt(dmcyt)(2)Ag-2][NO3](2) 1 was prepared from trans-[Pt(NH(2)Me)(2)(Hdmyct-N-3)(2)] [NO3](2) and AgNO3 at alkaline pH. and its crystal structure determined. The Pt ... Ag distances within the trinuclear cation are 2.892(1) and 3.040(1) Angstrom. The compound is compared with related mixed Pt-Ag nucleobase complexes as well as other trinuclear d(10)-d(8)-d(10) systems. Despite the problem of differentiation of the nucleobase arrangement (head-to-head or head-to-tail) due to the pseudo-two-fold symmetry of the 1,5-dimethylcytosine ligand, the head-to-head orientation has unambiguously been established by use of H-1 NMR spectroscopy following precipitation of AgCl.