ANALYTIC APPLICATIONS OF OXOCARBONS .2. COMPOSITION OF TUNGSTEN COMPLEXES OF BROMANILATE AND CHLORANILATE IONS - SPECTROPHOTOMETRIC DETERMINATION OF TUNGSTEN(VI)

The complexes formed from tungsten(VI) and chloranilate (C2-) and bromanilate (B2-) have been studied in aqueous solution and as solids, by ultraviolet, visible and infrared spectroscopy. At pH 3-4, the complexes have the composition ligand:tungsten = 2. At pH < 2, only the 1:1 complexes are found. The two reagents allow the spectrophotometric determination of W(VI) (λ, = 335 nm for H2C and 340 nm for H2B) in 1.4M HClO4, at concentrations of about 1 mg/l. The conditional stability constants of the two 1:1 complexes in this medium have been calculated. The tungsten complexes are more stable than the corresponding molybdenum complexes, and the complexes of B2- are more stable than the complexes of C2- [with W(VI) and Mo(VI)]. It is shown that this result is due to the difference between the pK1, values of the acids H2B and H2C. The infrared spectra of the complexes of B2- and C2- with Mo(VI) and W(VI) are discussed in order to define the interaction between the metal ions and the ligands. © 1979.