Reactions of Mo(VI) with (2 R,3 R)-tartaric acid in diluted aqueous solutions: a study by circular dichroism spectrophotometry

Abstract

The reactions between molybdenum(VI) and (2 R,3 R)-tartrate in aqueous solutions with C L/ C Mo ⩾ 1, pH between 1.5 and 6.0 and metal concentration between 1.0 × 10 −4 and 2.5 × 10 −2 mol dm −3 were studied by circular dichroism and UV spectrophotometry, at room temperature. At least four species were observed, their relative importance in solution varying with the molybdenum concentration, C L/ C Mo relation, pH and ionic medium. Three of them were identified with species previously observed by NMR spectroscopy. The fourth species is probably polymeric, with L/M < 1. The influence of the nature of different electrolytes in solution is reported. The formation constant for the complex [MoO 2(TH −1) 2] 4−, TH 2 = (2 R,3 R)-tartaric acid, was determined, the value log K = 16.2 ± 0.2 being found from solutions with I = 1 mol dm −3, NaCl and T = 18 ± 1 °C. Similar reactions between tungsten(VI) and the ligand are also discussed.