Molecular, supramolecular and solution structures of peroxovanadium complexes with ON and O3N donor set ligands: two new types of cationic–anionic peroxovanadium(v) peroxovanadates(v)

Abstract

The complexes, [VO(O₂)(pa)₂]ClO₄·3H₂O (1), [VO(O₂)(pa)₂][VO(O₂)₂(pa)]·3H₂O (2), [VO(O₂)(pa)₂][VO(O₂)(ada)]·2H₂O (3) and [VO(O₂)(pa)(pca)]·H₂O (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–H⋯O_p bonds [d(H⋯O_p) ∼ 2.0 Å]. The supramolecular structure of 1 is formed by a network of hydrogen bonds and strong attractive intermolecular π–π 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 Å]. The pa and pca ligands are ON coordinated via the oxygen atoms of the C(NH₂)O and COO⁻ groups, respectively, and nitrogen atoms of the heterocyclic rings, and ada as a tetradentate O₃N ligand. The thermal analysis of 4 showed that the loss of water of crystallization and the active oxygen release (T_min/°C 82, T_max/°C 165) are, under given conditions, individual processes separated by the temperature interval 90–132 °C. The solution structures and stability were studied by UV-VIS and ⁵¹V NMR spectroscopies.