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).

以三齿ONO席夫碱配体——2-羟基苯甲酰肼的2-羟基苯甲酰腙（H₂L），在乙醇介质中与二(乙酰丙酮)合氧钒(IV) [VO(acac)₂]反应，得到氧乙氧基钒(V)配合物[VO(OEt)L]（记为配合物A）；该配合物可与吡啶作用生成[VO(OEt)L·py]（记为配合物1）。配合物1经结构表征，其V(V)配位中心周围为畸变八面体O₄N₂配位环境。配合物A与1均可在乙醇介质中与碱性强于吡啶的中性单齿路易斯碱（包括2-甲基吡啶、3-甲基吡啶、4-甲基吡啶、4-氨基吡啶、咪唑及4-甲基咪唑）反应，生成通式为BH[VO₂L]的二氧钒(V)配合物。此类二氧配合物大多经结构表征，其中配阴离子[VO₂L]⁻呈现畸变四方锥结构。将BH[VO₂L]配合物在醇（ROH）中的溶液或悬浮液，用同醇介质中的HCl溶液处理，可转化为相应的单氧烷氧基钒(V)配合物[VO(OR)L]，其中R来自反应所用的醇溶剂。配合物A与1均可与4,4'-联吡啶反应，生成4,4'-联吡啶桥联双核配合物[VO(OEt)L]₂(μ-4,4'-bipy)（记为配合物2），据我们所知，该配合物为首例经结构表征的4,4'-联吡啶桥联氧钒(V)双核配合物。此外，本研究还合成并表征了另外2种结构类似的双核氧钒(V)配合物3和4。所有上述双核配合物（2~4）经碱B处理后，均可转化为对应的单核二氧钒(V)配合物（5~10）。