Purine N(1)-oxide complexes with 3d metal perchlorates

Abstract

A series of purine N(1)-oxide (LH) complexes with 3d metal perchlorates were synthesized by relfuxing mixtures of ligand and salt in ethanol–triethyl orthoformate. In one case (M = Cr 3+), an apparently hexacoordinated monomeric complex of the [Cr(LH) 2(C 2H 5OH) 2(OClO 3) 2](ClO 4 type, with terminal imidazole nitrogen-bonded LH was isolated (N(7) and N(9) are considered as equally likely binding sites for terminal unidentate LH). A number of pentacoordinated M 2+ complexes of the M(LH) 2(C 2H 5OH)(ClO 4) 2 type (M = Mn, Fe, Ni, Cu, Zn) seem to contain exclusively bidentate bridging LH, coordinated through the O(1) oxygen and one of the imidazole nitrogens (most probably N(7)); whereas, Co(LH) 2(C 2H 5OH) 2(ClO 4) 2 (pentacoordinated) and Fe(LH) 3(ClO 4) 3 (hexacoordinated) involve both bidentate bridging ligands of the preceding type and terminal unidentate imidazole nitrogen-bonded LH groups. Since all of the new polymeric complexes show normal ambient temperature magnetic moments, structural types involving MLHMLH bridges were considered as most probable. Simple linear chain-like structures wityh MLHMLH sequences were proposed for the Co 2+ and Fe 3+ complexes (the latter compound also contains a bidentate O 2ClO 2 ligand per Fe 3+ ion), whilst for the Mn +, Fe +, Ni 2+, Cu 2+ and Zn 2+ compounds, a more complicated structural type, involving cross-linking of linear chains of thepreceding type, seems to be most likely.