[(Ethylenediamine)Pt(uracilate)]4 – A Metal Analogue of Calix[4]arene: Coordination Chemistry of Its 1,3-Alternate Conformer towards First-Row Transition-Metal Ions

The open “molecular box” [(en)Pt(U-N1,N3)]4 (1) (where en = ethylenediamine, U = uracil dianion) is able to act as an efficient ligand for additional metal ions. Reactions of the 1,3-alternate conformer of 1 with divalent metal ions result in the formation of octanuclear compounds of the general formula [(en)Pt(U-N1,N3,O2,O4)M]4X8 [M = Cu2+, X = Cl (2a), X = (SO4)0.5 (2b), and M = Co2+ (3), Ni2+ (4), Zn2+ (5) with X = (SO4)0.5], in which the heterometals are bound at the exocyclic oxygen atoms of the uracil nucleobases. The structurally characterized heteronuclear compounds show a 1,3-alternate arrangement of the uracil nucleobases. Pt–M contacts are in the range 2.743(2)–2.804(2) Å; the Pt atoms act as weak σ donors to the heterometals. In spite of the high degree of positive charge associated with compounds 2a–5, they do not behave as hosts for anions. This is a consequence of the orientation of the four nucleobases which, in contrast to a cone arrangement, does not produce a sufficiently large cavity for the incorporation of anions.