Solution study of a structurally characterized monoalkoxo-bound monooxo-vanadium(V) complex: spontaneous generation of the corresponding oxobridged divanadium(V,V) complex and its electroreduction to a mixed-valence species in solution.

An interesting transformation of a structurally characterized monooxoalkoxovanadium(V) complex [VO(OEt)L] (LH 2 = a dibasic tridentate ONO donor ligand) in solution leading to the formation of the corresponding monooxobridged divanadium(V,V) complex (VOL) 2O is reported. This binuclear species in solution is adequately characterized by elemental analysis, measurement of conductance (in solution), various spectroscopic (UV-vis, IR, NMR, and mass spectrometry) techiniques and by cyclic voltammetry. The corresponding mixed-valence vanadium(IV,V) species has been generated in CH 3CN solution by controlled potential electrolysis of (VOL) 2O. This mixed-valence species is identified and studied by EPR technique (at room temperature and at liquid nitrogen temperature) and also by UV-vis spectroscopy. This study may be regarded as a general method of obtaining monooxo-bridged binuclear vanadium(V,V) species from the corresponding mononuclear monooxoalkoxovanadium(V) complexes of some selected dibasic tridentate ONO chelating ligands, which can be utilized as the precursor of monooxobridged divanadium(IV,V) mixed-valence species in solution obtainable by controlled potential electrolysis.

Simple general method of generating non-oxo, non-amavadine model octacoordinated vanadium(IV) complexes of some tetradentate ONNO chelating ligands from various oxovanadium(IV/V) compounds and structural characterization of one of them.

A simple general route of obtaining very stable octacoordinated non-oxovanadium(IV) complexes of the general formula VL2 (where H2L is a tetradentate ONNO donor) is presented. Six such complexes (1-6) are adequately characterized by elemental analysis, mass spectrometry, and various spectroscopic techniques. One of these compounds (1) has been structurally characterized. The molecule has crystallographic symmetry and has a dodecahedral structure existing in a tetragonal space group Pn2. The non-oxo character and VL2 stoichiometry for all of the complexes are established from analytical and mass spectrometric data. In addition, the non-oxo character is clearly indicated by the complete absence of the strong nuV=O band in the 925-1025 cm-1 region, which is a signature of all oxovanadium species. The complexes are quite stable in open air in the solid state and in solution, a phenomenon rarely observed in non-oxovanadium(IV) or bare vanadium(IV) complexes.

Synthesis, reactivity, and X-ray crystal structure of some mixed-ligand oxovanadium(V) complexes: first report of binuclear oxovanadium(V) complexes containing 4,4'-bipyridine type bridge.

Reaction of the tridentate ONO Schiff-base ligand 2-hydroxybenzoylhydrazone of 2-hydroxybenzoylhydrazine (H2L) with VO(acac)2 in ethanol medium produces the oxoethoxovanadium(V) complex [VO(OEt)L] (A), which reacts with pyridine to form [VO(OEt)L.(py)] (1). Complex 1 is structurally characterized. It has a distorted octahedral O4N2 coordination environment around the V(V) acceptor center. Both complexes A and 1 in ethanol medium react with neutral monodentate Lewis bases 2-picoline, 3-picoline, 4- picoline, 4-amino pyridine, imidazole, and 4-methyl imidazole, all of which are stronger bases than pyridine, to produce dioxovanadium(V) complexes of general formula BH[VO2L]. Most of these dioxo complexes are structurally characterized, and the complex anion [VO2L]- is found to possess a distorted square pyramidal structure. When a solution/suspension of a BH[VO2L] complex in an alcohol (ROH) is treated with HCl in the same alcohol, it is converted into the corresponding monooxoalkoxo complex [VO(OR)L], where R comes from the alcohol used as the reaction medium. Both complexes A and 1 produce the 4,4'-bipyridine-bridged binuclear complex [VO(OEt)L]2(mu-4,4'-bipy) (2), which, to the best of our knowledge, represents the first report of a structurally characterized 4,4'-bipyridine-bridged oxovanadium(V) binuclear complex. Two similar binuclear oxovanadium(V) complexes 3 and 4 are also synthesized and characterized. All these binuclear complexes (2-4), on treatment with base B, produce the corresponding mononuclear dioxovanadium(V) complexes (5-10).

Binary, Ternary, and Quarternary Complexes of Ruthenium(II) Involving the Flexidentate ONNS Donor Mono(4-(4-tolyl)thiosemicarbazone) of 2,6-Diacetylpyridine (L(2)H). First Report on Ruthenium Complexes of a Mono(thiosemicarbazone) of a Diketone: Crystal Structure of [Ru(L(2))(PPh(3))(2)]ClO(4).

A series of Ru(II) complexes of the ONNS donor ligand mono(4-(4-tolyl)thiosemicarbazone) of 2,6-diacetylpyridine (L(2)H) synthesized by using three different ruthenium-containing starting materials RuCl(3).xH(2)O, Ru(PPh(3))(3)Cl(2), and [Ru(NH(3))(5)Cl]Cl(2) are reported. Chemical and electrochemical studies of the complexes [Ru(L(2))(PPh(3))(2)]ClO(4) (1), [Ru(L(2))(PPh(3))(2)]Cl (2), [Ru(L(2))(PPh(3))]ClO(4).EtOH (3), [Ru(L(2))(PPh(3))(bpy)]ClO(4) (4), [Ru(L(2))(PPh(3))(ophen)]ClO(4) (5), [Ru(L(2))(2)] (6), and [Ru(L(2))(L(2)H)]Cl (7) have been carried out. The structure of the compound [Ru(L(2))(PPh(3))(2)]ClO(4) (1) has been determined by single-crystal X-ray diffraction techniques. The crystals are triclinic, space group P&onemacr; with a = 12.716(1) Å, b = 13.213(1) Å, c = 15.951(1) Å, alpha = 87.66(1) degrees, beta = 73.81(1) degrees, gamma = 70.93(1) degrees, and Z = 2, where the deprotonated ligand mono(4-(4-tolyl)thiosemicarbazone) of 2,6-diacetylpyridine (L(2)) is chelated to the Ru(II) center through the oxygen of the carbonyl group, pyridine ring nitrogen, imine nitrogen, and the thiolate sulfur atoms. Strong coordination of the carbonyl group suggested from its IR spectral characteristics has been confirmed from the appreciable shortening of the Ru-O bond and lengthening of the C=O bond in the structure of 1.