Crystal structures of a protonated form of trans-[Pt(NH3)2(mura)2] and of a derivative containing three different metal ions, Pt2+, Ag+, and Na+ (mura = 1-methyluracilate). Major difference in packing between heteronuclear pyrimidine nucleobase complexes of cis- and trans-(NH3)2PtII

Abstract

The complex trans-[Pt(NH₃)₂(mura)₂] 1 (mura = 1-methyluracilate), a compound of very low water solubility, is markedly solubilised in the presence of acid or suitable metal salts due to protonation and metal binding to the exocyclic oxygen atoms, respectively. The perchlorate salt trans-[Pt(NH₃)₂(Hmura)₂][ClO₄]₂·2H₂O 2 has been characterised by X-ray analysis. With Ag⁺, 1 formed heteronuclear species of varying stoichiometries, e.g. Pt₂Ag₃ 3, the composition of which can be further varied by the presence of alkali metal salts. The complex trans-[{Pt(NH₃)₂(mura)₂}₂AgNa(H₂O)₄][ClO₄]₂·6.5H₂O 4 appears to be the first structurally characterised example of a nucleobase complex containing three different metal ions. Tetranuclear cations of 4 are arranged in the crystal in such a way as to permit both intermolecular hydrogen bonding between NH₃ ligands and O² sites of mura nucleobases and π stacking between adjacent trans-[Pt(NH₃)₂(mura)₂] entities. This feature is radically different from that observed in related di- and tri-nuclear complexes derived from cis-(am)₂Pt^II. With mercury(II) salts initially binding to exocyclic oxygen atoms of the mura ligand takes place, followed by metal binding to the C⁵ atoms of both uracil ligands of 1.