Neutral peroxovanadium(v) complexes, [VO(O2)(pca)(bpy)] (1), [VO(O2)(pca)(phen)] (2) and [VO(O2)(pic)(pcaa)(H2O)].H2O(3), were synthesized [2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), pyrazinecarboxamide (pcaa), 2-pyrazinecarboxylic (Hpca) and picolinic (Hpic) acids]. Their X-ray single crystal analysis revealed a distorted pentagonal bipyramidal geometry in all complex molecules. The four "free" coordination sites of the vanadium atoms of the VO(eta2-O2)+ moieties in 1 and 2 are occupied by the donor atoms of two bidentate heteroligands. The supramolecular structures of 1 and 2 are exclusively constructed by intermolecular C--H(ar)...O hydrogen bonds [dH(H...O): 2.292-2.708 A (1), and 2.260-2.720 A (2)]. In addition, the structures are stabilized by parallel off-set pi-pi interactions between the bpy rings resp. non-parallel off-set interactions between the phen rings [centroid distances: 3.7000(1) A (1), 3.9781(2) and 3.6757(2) A (2)]. In the molecular structure of 3, pcaa is coordinated in an equatorial position of the bipyramid via the nitrogen atom of the pyrazine ring, while the aqua ligand is in the apical position. The disordered crystal water molecules are located in 1D channels oriented along the a axis. The intermolecular C-H(ar)...O hydrogen bonds in 3 were found within the dH(H..O) range 2.409-2.669 A. The pic ligands are off-set pi-pi stacked, with centroid distances: 3.6725(3) and 3.8323(3) A. The DFT orbital calculations and NBO analysis for the VO(eta2-O2)+ group gave evidence for a triple V[triple bond]O bond, and showed that the observed cis arrangement of the oxo and peroxo ligands results from the direct interaction between them. Experimental and calculated UV-Vis and IR spectral data are presented.
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.
Monoperoxovanadium(V) complexes, [NH3(CH2)2NH3][VO(O2)(ox)(pic)].2H2O (1) and [NH3(CH2)2NH3][VO(O2)(ox)(pca)] (2) [NH3(CH2)2NH3 = ethane-1,2-diammonium(2+), ox=oxalate(2-), pic=pyridine-2-carboxylate(1-), pca=pyrazine-2-carboxylate(1-)], were synthesized and characterized by X-ray analysis, IR and Raman spectroscopies. The five equatorial positions of the pentagonal bipyramid around the vanadium atoms are occupied by the eta2-peroxo ligand, two oxygen atoms of the ox, and the nitrogen atom of the pic or pca ligands, respectively. The oxo ligand and the oxygen atom of pic or pca are in the axial positions. Networks of X-HO (X=C, N or O) hydrogen bonds, and pi-pi interactions between aromatic rings in and anion-pi interactions in , determine the molecular packings and build up the supramolecular architecture. Three stereochemical rules for occupation of the donor sites in two-heteroligand [VO(O2)(L1)(L2)] complexes (L1, L2 are bidentate neutral or differently charged anionic heteroligands providing an OO, NN or ON donor set) are discussed. and crystallize as racemic compounds. The 51V NMR spectra proved that the parent complex anions of and partially decompose on dissolution in water to the monoperoxo-ox, -pic or -pca complexes.
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