Molecular, supramolecular and solution structures of peroxovanadium complexes with ON and O3N donor set ligands: two...

The complexes, [VO(O(2))(pa)(2)]ClO(4).3H(2)O (1), [VO(O(2))(pa)(2)][VO(O(2))(2)(pa)].3H(2)O (2), [VO(O(2))(pa)(2)][VO(O(2))(ada)].2H(2)O (3) and [VO(O(2))(pa)(pca)].H(2)O (4)[pa = picolinamide, ada = carbamoylmethyliminodiacetate(2-) and pca = 2-pyrazinecarboxylate(1-)], were synthesized. 2 and 3 are new types of peroxovanadium complexes: monoperoxovanadium diperoxovanadate (2) and monoperoxovanadium monoperoxovanadate (3). The complexes were characterized by chemical analysis and IR spectroscopy, and 1, 3 and 4 also by X-ray analysis. The structure of 1 is disordered, with alternating positions of the oxo and peroxo ligands. The peroxo oxygen atoms, O(p), in 1 are involved in weak hydrogen bonds with water molecules and close intramolecular C-HO...(p) bonds [d(HO(p)) approximately 2.0 A]. The supramolecular structure of 1 is formed by a network of hydrogen bonds and strong attractive intermolecular pi-pi interactions between the pyridine rings. The supramolecular architecture in 4 is constructed by (N,O)-H...O hydrogen bonds between the neutral complex molecules and water of crystallization. The peroxo oxygen atoms in 4 form intramolecular C-H...O(p) bonds [d(H...O(p))= 2.303 A]. The pa and pca ligands are ON coordinated via the oxygen atoms of the C(NH(2))=O and COO(-) groups, respectively, and nitrogen atoms of the heterocyclic rings, and ada as a tetradentate O(3)N ligand. The thermal analysis of 4 showed that the loss of water of crystallization and the active oxygen release (T(min)/ degrees C 82, T(max)/degrees C 165) are, under given conditions, individual processes separated by the temperature interval 90-132 degrees C. The solution structures and stability were studied by UV-VIS and (51)V NMR spectroscopies.