Stereochemistry of Vanadium Peroxido Complexes: The Case of the Quinoline-2-carboxylato Ligand.

A new mononuclear vanadium peroxido complex [VO(O2)(phen)(quin)]·H2O (1) exhibiting an unprecedented isomerism of its ligands was isolated from a two-component water-acetonitrile solvent system. DFT computations aimed at inspecting the stability of all possible isomers of complexes [VO(O2)(L1)(L2)], where L1 and L2 are NN+ON, OO+ON, NN+OO, and ON+ON donor atom set ligands, suggested that every complex characterized so far was the one preferred thermodynamically. However, the particular case of complex [VO(O2)(phen)(quin)] reported herein poses a notable exception to this rule, as this complex yielded single crystals of the isomer with total energy above the anticipated isomer, although both of these isomers could be observed concurrently in solution and also in the solid state. 51V NMR spectroscopy suggested these isomers to be present both in the crystallization solution and in the acetonitrile solution of 1. The coexistence of two isomers is a consequence of their small computed energy difference of 2.68 kJ mol-1, while the preferential crystallization favoring the unexpected isomer is likely to be triggered by solvent effects and the effects of different solubility and/or crystal packing. The coordination geometry of the unusual isomer also manifests itself in FT-IR and Raman spectra, which were corroborated with DFT computations targeted at band assignments.

Interpretation of the multiple vanadium-oxygen bonds in the central VO(eta2-O2)+ group. Synthesis, structure, supramolecular interactions and DFT studies for complexes with 2,2'-bipyridine, 1,10-phenanthroline, pyrazinato(1-) and pyrazinamide ligands.

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.

Hexakis[3-(aminocarbonyl)pyridinium] decavanadate(V) dihydrate.

The structure of the title compound, (C(6)H(7)N(2)O)(6)[V(10)O(28)].2H2O, at 120 (2) K has monoclinic (C2/c) symmetry. The asymmetric unit consists of one half-decavanadate anion of Ci symmetry, three cations and one water molecule. Each water molecule is hydrogen bonded to two decavanadate anions, thus forming a one-dimensional chain of anions. The three-dimensional supramolecular structure is formed by a network of N-H...O, O-H...O and C-H...O hydrogen bonds, in which the cations, anions and water molecules are involved, and by nonparallel-displaced pi-stacking interactions between pyridine rings. As a result of hydrogen bonding, the carboxamide groups of the cations are somewhat twisted from the pyridine ring plane.