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

Two binucelar oxidovanadium complexes, [(VO2)(2)(mu-Hpydn)(2)] (1) and [(VO)(2)(mu-pydn)(2)(bpy)(2)]center dot 5H(2)O (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 {(VO)-O-IV(mu-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. V-51 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.