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

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-aza-hypoxanthine 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.