A NEW TYPE OF DIVALENT METAL NUCLEOSIDATE COMPLEX - CRYSTAL-STRUCTURE OF TRANS-TETRAAQUOBIS(XANTHOSINATO)ZINC(II) DIHYDRATE

Several complexes of divalent transition metals with the anionic form of the purine nucleosides guanosine, inosine, and xanthosine have been isolated and characterized by thermal and spectroscopic techniques and magnetic measurements. The complexes have the general formula [M(Nuc)2(H2O)4].nH2O (except the cadmium complex, which has the formula [Cd(Xao)2(H2O)2].5H2O). The coordinated and uncoordinated water molecules are clearly identified by TG and DSC diagrams. The octahedral coordination for Mn, Co, Ni, and Cu is supported by the magnetic measurements. NMR data for cadmium xanthosinate indicate coordination through N3. The crystal structure of trans-[Zn(Xao)2(H2O)4].2H2O has been solved by X-ray diffraction. This is the first time that the structure of a xanthosine complex has been described and also the first description of the structure of a purine nucleoside complex with a divalent metal of the first transition series. The N7-coordinated xanthosinate is located at the apex of the octahedral complex. The structure reveals an interesting hydrogen-bonding scheme and unusual sugar conformations.