Electrochemistry of Isopoly and Heteropoly Oxometalates

Abstract

The sections in this article are Introduction Definitions General Properties, Literature, and Topics Covered A simplified Overview of the Formation of POMs Fundamental Redox Mechanisms of POMs at Electrodes Electrochemical Reductions of Selected Plenary POMs : α‐[ Si W 12 O 40 ] 4− , α‐[ PW 12 O 40 ] 3− , α‐[ P 2 W 18 O 62 ] 6− , and α‐[ H 2 W 12 O 40 ] 6− Aqueous Media Nonaqueous and Mixed Solvents Quinone/hydroquinone‐like Behaviors in the First Several Reduction Waves of POMs Selected Achievements that Illustrate the Basic Behaviors of Plenary POMs at Electrodes Heterogeneous One‐electron Exchange of α‐[ Si W 12 O 40 ] 4− in Dimethylformamide The Reduction Potential of the One‐electron Wave and the Role of the Central Heteroatom Isomerization upon Reduction POM ‐solvent Interactions as Probed by the Redox Potentials of Two POMs Structure of Electrolyte Solutions As Probed by the Electrochemical Behaviors of POMs Cation and Pressure Effects on the Electrochemistry of 12‐Tungstocobaltate and 12‐Tungstophosphate Ions in Acidic Aqueous Solution Mixed Addenda and Other Substituted POMs Comparison of Valence Trapping in Uniform and Mixed Addenda Plenary POMs Lacunary and Transition Metal–substituted POMs Lacunary POMs Transition Metal–monosubstituted POMs An Interesting Case of Mixing up of Substituent and Tungsten Waves: α 1 ‐ and α 2 ‐[ Fe III ( OH 2 ) P 2 W 17 O 61 ] 7− Sandwich‐type POMs Electron Transfer Behaviors of Multi‐iron Sandwich‐type POMs Electrochemical Probing of Siderophoric Behavior in Sandwich‐type Multi‐iron Wells–Dawson Heteropolytungstates Recent Developments Electrochemistry of a New Family of Wells–Dawson Anions: Semivacant Tungstophosphates and Arsenates [ H 4 XW 18 O 62 ] 7− ( X = P or As) Evidence for an Influence of the Dissymmetry on the Voltammetric Behavior of PW 18 : Comparison with P 2 W 18 Recent Achievements in Apparently Direct Multiple Electron Transfers on the First Waves of POMs Electrochemistry of the Multi‐nickel Polyoxoanions [ Ni 6 As 3 W 24 O 94 ( H 2 O ) 2 ] 17− , [ Ni 3 Na ( H 2 O ) 2 ( As W 9 O 34 ) 2 ] 11− , and [ Ni 4 Mn 2 P 3 W 24 O 94 ( H 2 O ) 2 ] 17− Electrochemistry of the Iron(III)‐substituted Keggin Dimer, [ Fe 6 ( OH ) 3 (A‐α‐ Ge W 9 O 34 ( OH ) 3 ) 2 ] 11− Theoretical Approaches Electronic Structures of POMs Explain their Redox Behaviors and the Relative Stability of Reduced Forms An Extended Hückel Calculations Approach to a Qualitative Understanding of the Initial Electron Transfer Site in Dawson‐type POMs Electrocatalysis Basic Concepts of Homogeneous Catalysis of Electrode Reactions Selected Electrocatalysis in Homogeneous Solution Electrocatalytic Reductions Electrocatalytic Oxidations Conclusion Acknowledgment

Rational Synthesis, Structure, Magnetism and Electrochemistry of Mixed Iron–Nickel‐Containing Wells–Dawson‐Fragment‐Based Sandwich‐Type Polyoxometalates

“…To keep a recent example, a supramolecular compound like [P 8 W 48 O 184 ] 40-, with only W centres, can also be used to reduce NO efficiently. [48,53] In the present pH 1 experiments, the two processes HNO 2 i H + + NO 2 -, pK a = 3.3 at 18°C and 3 HNO 2 i HNO 3 + 2 NO + H 2 O indicate that nitrous acid might be the reactive intermediate. Figure 7 compares the CVs, in a pH 1 medium, restricted to Fe III reduction potential domain for Fe2_Ni2As4 and Ni2_Fe2As4 upon addition of nitrite (γ = 30).…”

“…[48,49] Complementary data can be found in Table S2 and the Supporting Information. We now come to the comparison of the CVs of Fe2_ Ni2As4 and Ni2_Fe2As4.…”

“…In line with the studies we have undertaken for a few years now, [47] we are developing simple and rational procedures that may improve targeted syntheses of new POMs likely to play a major role in catalytic and electrocatalytic reactions. [48] In fact, it was found that the location, nature and number of the d metal centres in the POM framework may influence the interactions between redox-active centres within the molecule. n-(where X = As or P and y = 2, 3 or 4) towards the electroreduction of dioxygen is improved when the number of Fe atoms is increased.…”

Magnetic Bistability of Individual Single‐Molecule Magnets Grafted on Single‐Wall Carbon Nanotubes

“…[10] Such stepwise reductions constitute fingerprints of iron centers within iron-sandwich-type POMs. [15] Both the small anodic-to-cathodic peak potential separation for the waves and the linear variation of the peak current with the scan rate (shown for one tungsten wave, Figure 2 b) testify that Fe 6 -POM is grafted on the SWNTs. [16] Perfect reproducibility of the voltammogram during prolonged potential cycling confirms that the electrode is durable ( Figure S6 in the Supporting Information).…”

In situ measurement of the Preyssler polyoxometalate morphology upon electrochemical reduction: A redox system with Born electrostatic ion solvation behavior

“…In principle, SANS (small-angle neutron scattering), and measurements of diffusion coefficients for the determination of hydrodynamic radii [74] may well be engaged to provide insight into this ancillary issue. Similarly, as concerns solute effects (e.g., anion-cation pairing) [75], once again, our SAXS measurements of dilute Preyssler anion solutions in 1 M HCl electrolytes provide no information about protonation, a specialty which can be directly addressed by pH-dependent voltammetry measurements [76]. Both of these subjects, although of contemporary interest in POM sciences, are outside of the scope of design and performance of this work on the effects of reduction on the P-W-O framework morphology.…”