VO(IV) complexes of 3-hydroxypicolinic acid: a solution study and the structure of a supramolecular assembly in the solid state

Abstract

The complex formation between oxovanadium(IV) and 3-hydroxypicolinic acid (3HPA) was studied in aqueous solution and in the solid state. The ligand displays ambidentate binding properties [Polyhedron 19 (2000) 55]: it forms picolinate-type (N, COO −), salicylate-type (COO −, O −) and mixed-type complexes involving bidentate coordination of the ligand. It can also coordinate in a tridentate way, via the (N, COO −, O −) donor set, forming a tetrameric species. Two of complexes formed in equilibrium in solution were isolated in the solid state too: VOH 2(3HPA) 2 and [VO(3HPA)] 4. The latter was characterized crystallographically; the binding mode was found to be identical in solution and in the solid state. The binding properties of the ligand were compared with those of other substituted picolinic acid derivatives. A possible relationship between the insulin-mimetic activity and the structure of these complexes is discussed.