The biological activity of the vanadium Schiff base complexes, which can be potentially
used as insulin-mimetic compounds, was extensively studied in the last decade. Pharmacological
data showed that these compounds produced a significant decrease in blood glucose level and
improved liver and kidney function after two weeks of daily use. The vanadium complexes obtained
so far with Schiff bases create problems, most often with cytotoxicity, very low solubility in water,
difficulty in studying the crystal structure, instability at pH = 2 and transport to cells. Therefore,
it is necessary to search for new organic vanadium compounds to optimize their pharmaceutical
activity. Lastly, several hundred vanadium(III–V) complexes with Schiff bases were tested, controlling
both the starting vanadium compound for the synthesis of complexes, as well as changing
the substituents in the aromatic ring of aldehyde and hydrazide—Schiff base components. The
obtained neutral compounds were highly soluble in organic solvents; however, they were insoluble
in water. Therefore, the DMSO-H2O mixture was used to test the stability of the complexes. In the
last studies, the synthesis and physicochemical characterization of the vanadium(V) complex with triethylamine
as a cation—HTEA[VO2(L)] (where L = Schiff base formed from 5-bromosalicylaldehyde
and 2-hydroxybenzhydrazide)—was described. In the formed ionic complexes, the crystal studies
show additional hydrogen interactions between the cation and the complex anion. The ionic structure
of such compounds should increase the solubility of the complexes in water, thus maximizing their
availability in the biological systems studied.