[(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-N-1,N-3)](4) (1) (where en = ethylenedia mine, U = uracil dianion) is able to act as an efficient Ligand for additio nal 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-N-1,N-3,O-2,O-4)M](4)X-8 [M = Cu2+, X = Cl (2a), X = (SO 4)(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 urac il are bound at the nucleobases. The structurally characterized heteronucle ar compounds show a 1,3-alternate arrangement of the uracil nucleobases. Pt -M contacts are in the range 2.743(2)-2.804(2) Angstrom; the Pt atoms act a s weak sigma donors to the heterometals. In spite of the high degree of pos itive charge associated with compounds 2a-5, they do not behave as hosts fo r anions. This is a consequence of the orientation of the four nucleobases which, in contrast to a cone arrangement, does not produce a sufficiently l arge cavity for the incorporation of anions.