[Applications analytiques des oxocarbones-II: composition des complexes tungstiques des ions bromanilate et chloranilate: dosage spectrophotometrique du tungstene(VI)].
The complexes formed from tungsten(VI) and chloranilate (C(2-)) and bromanilate (B(2-)) 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) (lambda, = 335 nm for H(2)C and 340 nm for H(2)B) in 1.4M HClO(4), 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 B(2-) are more stable than the complexes of C(2-) [with W(VI) and Mo(VI)]. It is shown that this result is due to the difference between the pK(1), values of the acids H(2)B and H(2)C. The infrared spectra of the complexes of B(2-) and C(2-) with Mo(VI) and W(VI) are discussed in order to define the interaction between the metal ions and the ligands.
Poirier
J M
JM
Laboratoire de Chimie Analytique, Université René Descartes, 4, avenue de l'Observatoire, 75006 Paris, France.
Verchere
J F
JF