Interaction of vanadium(III) with imidazole carboxylic acids

Complex formation between vanadium(III) and several imidazole carboxylic derivatives (urocanic acid, imidazole-4-carboxylic and imidazole-4,5-dicarboxylic acid) was studied using pH-potentiometric and spectroscopic (UV–Vis absorption and fluorescence) methods. The results show that urocanic acid is a weak ligand in aqueous solution and hydrolysis of vanadium(III) effectively competes with the complexation processes. Imidazole mono and di-carboxylate are relatively stronger donor (N,O) ligands and are able to prevent, to some degree, the hydrolysis processes. The main complex species in the vanadium(III)–imidazole-4,5-dicarboxylic acid system is the dinuclear μ-oxo bridged V2OL2 species.In the vanadium(III)–imidazole-4-carboxylic acid system formation of several mononuclear (ML, ML2, MLH−1, and ML2H−2) and dinuclear (M2L2H−2 and M2L4H−2) μ-oxo bridges species have been observed in the pH range 2–9.We have isolated a solid compound of vanadium(III) with the urocanate ligand in the microcrystalline form from a non-aqueous solvent (tetrahydrofuran). This compound has interesting luminescent properties, which result in an effective energy transfer from the ligand molecule to the d-electronic V3+ states.

Graphical abstractComplex formation between vanadium(III) and several imidazole carboxylic derivatives (urocanic acid, imidazole-4-carboxylic and imidazole-4,5-dicarboxylic acid) was studied using pH-potentiometric and spectroscopic (UV–Vis absorption and fluorescence) methods. The results show that urocanic acid is a weak ligand in aqueous solution and hydrolysis of vanadium(III) effectively competes with the complexation processes. Imidazole mono and di-carboxylate are relatively stronger donor (N,O) ligands and are able to prevent, to some degree, the hydrolysis processes. The main complex species in the vanadium(III)–imidazole-4,5-dicarboxylic acid system is the dinuclear μ-oxo bridged V2OL2 species.Figure optionsDownload full-size imageDownload as PowerPoint slide