Cytosine nucleobase as a tridentate ligand: metal binding to N(3), N(4) and O(2) in trans-[(NH2Me)2Pt(dmcyt)2Ag2][NO3]2(dmcyt = 1,5-dimethylcytosinate)

Abstract

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-[(NH₂Me)₂Pt(dmcyt)₂Ag₂][NO₃]₂1 was prepared from trans-[Pt(NH₂Me)₂(Hdmyct-N³)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)Å. The compound is compared with related mixed Pt–Ag nucleobase complexes as well as other trinuclear d¹⁰–d⁸–d¹⁰ 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 ¹H NMR spectroscopy following precipitation of AgCl.