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(μ-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).