Janine Lagrange

Complex formation of peroxouranyl (and uranyl) with polyaminocarboxylate ligands

Abstract Complexation of the uranyl ion (UO 2 2+ ) and of the peroxouranyl species (UO 4 ) by some polyaminocarboxylate ligands has been investigated in solution (3M NaClO 4 ) at 25°C. The logarithms of the cumulative formation constants of the UO 2 2+ chelates formed are: UO 2 edta 2− (15.65), UO 2 Hedta − (18.59), (UO 2 ) 2 edta (20.24); UO 2 edda (16.02); UO 2 Hnta (12.19); UO 2 ida (9.63), UO 2 H 2 (ida) 2 (23.80). The equilibrium UO 2 2+ + H 2 O 2 ⇌ UO 4 + 2H + has a stability log K = −3.99. The peroxocomplexes formed are UO 4 Hedda − (14.81, expressed from UO 2 2+ and H 2 O 2 ) and UO 4 Hnta 2− (8.50). Solution structures of the chelates are proposed.

Determination and comparison of stability constants of vanadium(V), molybdenum(VI), and tungsten(VI) aminocarboxylate complexes

The solution structure and equilibria of vanadium(V), molybdenum(VI), and tungsten(VI) complexes formed by ethylenediaminetetra-acetic (H4edta), ethylenediamine-NN′-diacetic (H2edda), nitrilotriacetic (H3nta), and iminodiacetic (H2ida) acids have been investigated potentiometrically and spectrophotometrically. If Yn– represents the fully dissociated ligand anion, all the 1 : 1 complexes have the formula [VO2Y](n–1)–, [MoO3Y]n–, and [WO3Y]n–. A 1 : 2 vanadium(V)-ida, a 2 : 1 molybdenum(VI)- or tungsten(VI)–edta and two protonated 1 : 1 vanadium(V)–edta chelate complexes are also formed. The formation constants of the 1 : 1 complexes increase with the number of chelate rings for the same metal and decrease from VV to MoVI and WVI for a given ligand. The oxometal ions have a greater affinity for the nitrogen of the amine function than for the acetate oxygen.

Kinetic study of acid dechelation of some vanadium(V)–aminocarboxylate complexes in aqueous solution

Kinetic studies of the acid hydrolysis of vanadium(V) complexes of ethylenediaminetetra-acetic acid (H4edta), ethylenediamine-N,N′-diacetic acid (H2edda), and nitrilotriacetic acid (H3nta) have been carried out by stopped-flow spectrophotometry in aqueous solution (I= 3 mol dm–3, NaClO4). The observed first-order (with respect to chelate) rate constant increases as a hyperbolic-type function with H+ concentration. Discussion of the differences in reactivity of the chelates indicates that the dissociation of the chelate complexes would proceed by a pre-equilibrium step leading to the formation of an intermediate for which the ketonic oxygen of one carboxylate group of the chelate is protonated. This first step is followed by rupture of a metal–oxygen bond, rupture of a metal–nitrogen bond, and then by complete cleavage of the multidentate ligand.

Mechanism of the Homogeneous Liquid Oxidation of Sulphur(IV) to Sulphur(VI) by Hydrogen Peroxide

This work is a contribution to elucidate the mechanism of the S(IV) oxidation by hydrogen peroxide in atmospheric water droplet. This laboratory study has been done by stopped-flow spectrophotometry. In order to determine the factors which should give interfering reactions, the kinetic study was performed, at first, in sodium Perchlorate medium. This medium does not give interference, but stabilizes only the activity factors of the reacting species. Between pH 3 and 7, the reaction rate appears proportional to the H+, HSO3- and H2O2 concentrations. The influence of the buffers used was studied. After this fundamental study, the roles of anions as SO4 2- and C1- and of cations as Cu2+, Mn2+, Cr3+ and Fe3+ were determined in order to extrapolate the results to cloud or rain conditions.