Copper(II) perchlorate complexes with N-methyl substituted xanthines

Abstract

Monomeric complexes of the [CuL 2(OClO 3) 2] type (L = theophylline, theobromine, caffeine) were synthesized by refluxing 2:1 mixtures of N-methyl substituted xanthine and Cu(ClO 4) 2 in ethanol–triethyl orthoformate. Characterization studies suggest that the complexes are distorted tetrahedral with terminal unidentate L and -OClO 3 ligands. Most likely binding sites for caffeine and theophylline are the N(9) and N(7) imidazole nitrogens, respectively, in view of previously reported crystal structures of Cu 2+ complexes with these ligands. For the theobromine complex, the N(1) pyrimidine and N(9) imidazole nitrogens are almost equally likely to function as the binding site.