
TY  - JOUR
A1  - Dunne, SJ 
A1  - Burns, RC 
A1  - Lawrance, GA 
T1  - Oxidation of Nickel(II) and Manganese(II) by Peroxodisulfate in Aqueous Solution in the Presence of Molybdate. Crystal Structure of the (NH<sub>4</sub>)<sub>6</sub>[NiMo<sub>9</sub>O<sub>32</sub>].6H<sub>2</sub>O Product
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 1992
VL  - 45
IS  - 12
SP  - 1943
EP  - 1952
KW  - 
UR  - https://doi.org/10.1071/CH9921943 
N2  - Oxidation of Ni2+,aq, by S2O82- to nickel(IV) in the presence of molybdate ion, as in the analogous manganese system, involves the formation of the soluble heteropolymolybdate anion [MMogO32]2- (M = Ni, Mn ). The nickel(IV) product crystallized as (NH4)6 [NiMogO32].6H2O from the reaction mixture in the rhombohedra1 space group R3, a 15.922(1), c 12.406(1) Å ; the structure was determined by X-ray diffraction methods, and refined to a residual of 0.025 for 1741 independent 'observed' reflections. The kinetics of the oxidation were examined at 80 C over the pH range 3.0-5.2; a linear dependence on [S2O82-] and a non-linear dependence on l/[H+] were observed. The influence of variation of the Ni/Mo ratio between 1:10 and 1:25 on the observed rate constant was very small at pH 4.5, a result supporting the view that the precursor exists as the known [NiMo6O24H6]4- or a close analogue in solution. The pH dependence of the observed rate constant at a fixed oxidant concentration (0.025 mol dm-3) fits dequately to the expression kobs = kH [H+]/(Ka+[H+]) where kH = 0.0013 dm3 mol-1 s-1 and Ka = 4-0x10-5. The first-order dependence on peroxodisulfate subsequently yields a second-order rate constant of 0.042 dm3 mol-1 s-1. Under analogous conditions, oxidation of manganese(II) occurs eightfold more slowly than oxidation of nickel(II), whereas oxidation of manganese(II) by peroxomonosulfuric acid is 16-fold faster than oxidation by peroxodisulfate under similar conditions. 
ER  -

