Polyoxidovanadate complexes: synthesis, structures and catalytic oxidative bromination of phenol red.

By selecting appropriate ligands, two polyoxidovanadate complexes, [Ni(en)2]3[V18O42Cl]·7H2O·2H3O+(1) and [H2N(CH3)2]3[PV14O42]·2TMP·6H3O+(2), have been synthesized at different pH values using V2(SO4)3, Ni(CH3COO)2, and H6TTHA (for1), VO(acac)2and TPP (for2) (en = C2H8N2, TPP = thiamine pyrophosphate, TMP = thiamine monophosphate, H6TTHA = 1,3,5-triazine-2,4,6-triamine hexaacetic acid). The complexes have been characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis (TG), and single crystal X-ray diffraction. The complexes catalyze the oxidation of the organic substrate phenol red in the presence of H2O2and bromide, and the reaction system is considered as a model for hydrogen peroxide determination. The reaction rate constants (k) for1and2are calculated as 3.729 × 103and 4.083 × 103(mol L)−2 s−1. The maximum conversion rate of phenol red for1is 83.32%, while for2is 81.12%. [ABSTRACT FROM AUTHOR]