Voltammetric behavior of 1- and 4-[S₂V^VW₁₇O₆₂]⁵⁻in acidified acetonitrile

Abstract

Data derived from a voltammetric and spectroscopic study of the V(V/IV) couple associated with the initial reduction of the Wells-Dawson-type mono vanadium-substituted polyoxometalates, 1- and 4-[S2V(V)W17O62](5-) in CH3CN as a function of CF3SO3H acid concentration have been obtained. (51)V NMR (V(V) component) and EPR (V(IV) component) spectra were measured in CH3CN in the presence and absence of an acid. These data showed a small fraction of the 1-isomer in the 4-[S2V(V)W17O62](5-) sample and that protonation could occur at both redox levels for both isomers. On the basis of the mechanism postulated from the voltammetric and spectroscopic data, simulations of cyclic voltammograms were undertaken for the reduction of the isomerically pure 1-[S2V(V)W17O62](5-) isomer over a wide acid concentration range, and the results were compared with experimental data. Cyclic voltammograms of the V(V/IV) couple derived from the reduction of 1- and 4-[X2V(V)W17O62](7-) (X = P, As) were also obtained in CH3CN and the results were compared with those for 1- and 4-[S2V(V)W17O62](5-). Reversible potentials for the V(V/IV) couple are dependent on the anion charge of the polyoxometalate. Analysis of cyclic voltammograms obtained for 1- and 4-[S2V(V)W17O62](5-) in acetonitrile, acetone, dimethyl sulfoxide, dimethyl formamide and nitromethane showed that these V(V/IV) reversible potentials are also dependent on the acceptor numbers and the polarity index (E(T)(N)) values of the organic solvents.

New Path for Polyoxometalates: Controlled Synthesis and Characterization of Metal‐Substituted Tungstosulfates

“…On the other hand, all S 2 MW 17 show several reduction waves with different current magnitudes because the proton, which acts as a counter cation, is coupled with POMs without full dissociation in CH 3 CN. Similar reduction waves were observed for Keggin‐type POMs without protons as a counter cation in CH 3 CN in the presence of a small amount of acid . In addition to neutralizing S 2 MW 17 , reversible redox couples were obtained, as shown in by the red‐colored lines of Figure , without small redox waves, implying that only one type of isomer (the α 1 ‐form) is present, as mentioned above.…”

“…Vanadium‐substituted sulfur‐centered POMs, [SVM 11 O 40 ] 3– and [S 2 VM 17 O 62 ] 5– , have also been prepared in an aqueous CH 3 CN solution. [6l], The detailed voltammetric behavior of [SVM 11 O 40 ] 3– and [S 2 VW 17 O 62 ] 5– has been investigated in CH 3 CN containing designated concentrations of acid, elucidating that they exhibit a more positive redox potential than the parent POMs and the corresponding vanadium‐substituted POMs, [XVM 11 O 40 ] n – (X = Si, Ge, P, As; M = Mo, W) . In addition, these POMs have low proton‐association constants based on the simulation of the cyclic voltammograms of [SVM 11 O 40 ] 3– and [S 2 VW 17 O 62 ] 5– .…”

Polyoxometalates in Imidazolim-based Ionic Liquids: Acceptor Number and Polarity Estimated from Their Voltammetric Behaviour

“…[25][26][27] In addition, the first redox potentials observed in organic solvents were related to the AN and ET N of organic solvents, which indicates that the redox potentials of POMs can be used as a probe for the electrochemical determination of AN and ET N of various solvents. 27,28 Tetraphenylarsonium tetraphenylborate was selected as a standard compound for the determination of the transfer activity coefficients of individual cations and anions from water to organic solvents. 21 This compound consists of large, similarly sized monocations and monoanions with high symmetry, resulting in no specific interactions between the organic solvents and the ions due to the low and uniform surface charge density of the tetraphenylarsonium cations and the tetraphenylborate anions.…”

Diversity of Polyoxometalate‐Based Copper Compounds Obtained from the Same Reaction System

“…The peak potentials of anodic waves II shows shifts of 0.12 V between CPE 1 and CPE 2 or CPE 4 (Table ); therefore, wave II may be a result of an overlap of the waves for the oxidation of copper(I) centres and the further oxidation of Mo V centres. In this potential range, no redox peaks ascribed to vanadium should be observed, as it is present as a stable V V species in acidic solution . The anodic peak III appears only for CPE 2 and CPE 4 at a high overpotential as a one‐electron oxidation.…”