Interaction of Metal Ions with 7-Deaza-8-aza-and 8-Aza-purines Preparation and X-Ray Structural Analysis of Copper(II) Complexes

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Abstract
The reaction of 8-aza- and 7-deaza-8-aza-purines with Cu2+ cations in acid solution has been studied. At a pH value of 2, the 8-azaadenine complex [Cu(H2O)4(AAdH)2](NO3)2 (1), which displays Cu-N9 coordination; may be isolated from solution. The reaction of CuCl2 with 8-azahypoxanthine in concentrated HCl solution leads to ring opening at C2 of the azapurine with subsequent formation of dichlorobis[5-amino-4-carboxamide)[1-3]triazole]copper(II) dihydrate 2, in which the triazole ligands display a chelating function, coordinating the metal via N7 and O6. The results for 1 and 2 suggest that copper coordination of the azapurine base is not a prerequisite for opening of the pyrimidine ring. Respectively N9- and N8-coordinated complexes [CuCl3(AllH3)]n 3 and [CuCl2(H2O)(MAllH)]n (4) of allopurinol (AllH2) and 9-methylallopurinol (MAllH) may be prepared by the reaction of CuCl2 with the respective bases in HCl solution. In contrast, with the analogous 1-methyl-4-aminopyrazolo[3,4-d]pyrimidine MAPP, only the salt (MAPPH)4(Cu2Cl8) (5) could be isolated under similar conditions, indicating that N8 is less attractive as a binding site in this 7-deaza-8-azaadenine derivative. The structures of 1-5 have been established by X-ray structural analysis. A distorted octahedral [4+2]geometry is found for the copper atoms in 1 and 2. Chlorine bridged polymeric chain structures are adopted by the complexes 3 and 4. An intermediate coordination geometry between trigonal bipyramidal and square-pyramidal is observed for the metal atoms in 3, a distorted square-pyramidal geometry in 4.