Synthesis, structure and properties of a series of scorpionate oxovanadium(IV)–carboxylate complexes

A series of oxovanadium(IV) complexes: TpVO(pzH)(2,4-Cl–C6H3–OCH2COO) (1), TpVO(pzH)(C6H5–OCH2COO) (2), TpVO(pzH)(p-Cl–C6H4–COO) (3), TpVO(pzH)(3,5-NO2–C6H3–COO) (4), Tp∗VO(pzH∗)(p-Cl–C6H4–COO) (5) and Tp∗VO(pzH∗)(p-Cl–C6H4–COO) · CH3OH (6) (Tp = hydrotris(pyrazolyl)borate, pzH = pyrazole, Tp∗ = hydrotris(3,5-dimethylpyrazolyl)borate, pzH∗ = 3,5-dimethylpyrazole) were synthesized and their crystal structures were determined by X-ray diffraction. In all the complexes, the vanadium ions are in a distorted-octahedral environment with a N4O2 donor set. Hydrogen bonding interaction exists in each complex. Complexes 1 and 2 are hydrogen-bonded dimers. Dimeric units of 2 are connected to one another via weak inter-molecular C–H···O interactions to form a 2D network on the bc-face. In 3–6 there exist intramolecular N–H···O hydrogen bonds between the neutral pyrazole/3,5-dimethylpyrazole and the uncoordinated carboxyl oxygen atom. In addition, the catalytic activity of complex 2 in a bromination reaction in phosphate buffer with phenol red as a trap was evaluated by UV–Vis spectroscopy. Furthermore, the elemental analyses, IR spectra and thermal stabilities were recorded.

The one-step reaction of VOSO4 · nH2O, pyrazole or 3,5-dimethylpyrazole, potassium poly(pyrazolyl)borate and carboxylic acids in methanol resulted in six new complexes, 1–6. The synthetic process described here is different from those in literature reports. Structural analyses show that in all of these complexes, the vanadium atoms are six-coordinated with a N4O2 donor set in a distorted-octahedral geometry, the carboxylate groups are coordinated as monodentate and the uncoordinated oxygen atom of the carboxylate groups form intra- or inter-molecular hydrogen bonds with the NH group of the corresponding coordinated neutral pyrazole (pzH/pzH∗).Figure optionsDownload as PowerPoint slide