Synthesis, characterization, DFT calculations and bromoperoxidase activity of binuclear oxidovanadium complexes containing vitamin B6

Abstract

Two binucelar oxidovanadium complexes, [(VO2)2(µ-Hpydn)2] (1) and [(VO)2(µ-pydn)2(bpy)2]·5H2O (2), where pydn = pyridoxine and bpy = 2,2’-bipyridine, were synthesized and characterized by elemental analysis and infrared (IR), electron paramagnetic resonance (EPR), and electronic (UV-vis) spectroscopies. The structure of 2 was determined by single-crystal X-ray diffraction analysis. It is comprised of two distorted octahedral oxidovanadium(IV) centers with a terminal bpy ligand and bridged by the methoxido group of the pydn ligands, forming the {VIVO(µ-OR)2}2+ core with anti-orthogonal configuration. Density functional theory (DFT) calculations at the B3LYP/LANL2DZ level were used to obtain the optimized geometries and to study the electronic structure of 1 and 2. For 2, EPR analysis in the solid state, magnetic susceptibility measurements and the theoretical magnetic exchange coupling constant (J) of 20.1 cm−1 indicate a weak ferromagnetic coupling. 51V NMR and EPR spectroscopies suggest partial breakage of both binuclear structures in solution. Both complexes act as pre-catalysts for the bromination of phenol red to phenol blue in the presence of KBr, H2O2 and perchloric acid.