Electrochemistry and Homogeneous Self-Exchange Kinetics of the Aqueous 12-Tungstoaluminate(5−/6−) Couple

Czap, Almut; Neuman, Nancy I.; Swaddle, Thomas W.

doi:10.1021/ic060527y

Cited by 29 publications

(26 citation statements)

References 55 publications

(113 reference statements)

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“…In addition, some workers argue that setting the parameter r equal to the internuclear distance between reacting species is not justified, and that successful results obtained by doing so should be viewed as fortuitous. 30 Nonetheless, as is demonstrated later in this chapter, it can give excellent results in some cases. [31][32][33][34] Alternatively, one may use the Guggenheim equation (Equation 1.28), which is rigorously correct for solutions of mixed electrolytes.…”

Section: 29mentioning

confidence: 68%

Electron Transfer Reactions

Snir¹,

Weinstock²

2010

Physical Inorganic Chemistry

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Section: 29mentioning

confidence: 68%

Electron Transfer Reactions

Snir¹,

Weinstock²

2010

Physical Inorganic Chemistry

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“…[92] The truth is much more prosaic and derives from studies of isotope exchanges and electron exchanges (e.g. Czap et al [93] ), in oligomers and nanometre-sized oxide ions. As we discuss below, isotope-exchange into a structural bridge in these molecules requires formation of an intermediate structural form with lowered symmetry and accessible oxygens.…”

Section: Some Macroscopic Reactivity Trendsmentioning

confidence: 99%

Ligand- and oxygen-isotope-exchange pathways of geochemical interest

Casey¹

2015

Environ. Chem.

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Environmental context. Most chemical processes in water are either ligand-or electron-exchange reactions.Here the general reactivity trends for ligand-exchange reactions in aqueous solutions are reviewed and it is shown that simple rules dominate the chemistry. These simple rules shed light on most molecular processes in water, including the uptake and degradation of pesticides, the sequestration of toxic metals and the corrosion of minerals.Abstract. It is through ligand-exchange kinetics that environmental geochemists establish an understanding of molecular processes, particularly for insulating oxides where there are not explicit electron exchanges. The substitution of ligands for terminal functional groups is relatively insensitive to small changes in structure but are sensitive to bond strengths and acid-base chemistry. Ligand exchanges involving chelating organic molecules are separable into two classes: (i) ligand substitutions that are enhanced by the presence of the chelating ligand, called a 'spectator' ligand and (ii) chelation reactions themselves, which are controlled by the Lewis basicity of the attacking functional group and the rates of ring closure. In contrast to this relatively simple chemistry at terminal functional groups, substitutions at bridging oxygens are exquisitely sensitive to details of structure. Included in this class are oxygen-isotope exchange and mineraldissolution reactions. In large nanometer-sized ions, metastable structures form as intermediates by detachment of a surface metal atom, often from a underlying, highly coordinated oxygen, such as m 4 -oxo, by solvation forces. A metastable equilibrium is then established by concerted motion of many atoms in the structure. The newly undercoordinated metal in the intermediate adds a water or ligand from solution, and protons transfer to other oxygens in the metastable structure, giving rise to a characteristic broad amphoteric chemistry. These metastable structures have an appreciable lifetime and require charge separation, which is why counterions affect the rates. The number and character of these intermediate structures reflect the symmetry of the starting structure. Simple reactivity trends for ligand-and oxygen-isotope exchanges FormalismMost metals in aqueous solutions of interest to environmental chemists are coordinatively saturated. Here saturated is meant in the sense of Pauling's First Rule, relating ionic radius to oxygen packing. Most metals in water have the maximum number of coordinated atoms given by their radius ratios -exceptions certainly exist for highly covalent materials (e.g. Pt II , Nb V ), and some are discussed below, but most materials near the Earth's surface are oxides with a metal that has a fixed coordination or slightly variable number. In sharp contrast, the coordination

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“…Weinstock and co-workers [52,76] used a similar 27 Al NMR experiment to determine rate constants as a function of ionic strength in water for electron self-exchange between a series of AlW 12 (It should be noted, however, that at large electrolyte-cation concentrations, or when larger cations are present, Swaddle obtained data that suggest the self-exchange reaction between 3 ox and 3 1e is cation catalyzed. [78] )…”

Section: Electron Self-exchangementioning

confidence: 99%

The Reduction of Dioxygen by Keggin Heteropolytungstates

Snir

Wang

Weinstock

2011

Israel Journal of Chemistry

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Reversible redox chemistries are an inherent feature of numerous metal oxide cluster anions (POMs). Moreover, as discrete molecular structures with well‐defined and controllable solution chemistries, POMs can be deployed as physicochemical probes for studying inorganic reaction mechanisms. In the past decade, we have used an iso‐structural series of α‐Keggin heteropolytungstate cluster anions to systematically investigate a number of fundamental topics, including electron transfer to dioxygen. The iso‐structural series of cluster anions is obtained by varying the heteroatom, Xn+, in the plenary, Td‐symmetry α‐Keggin ion, Xn+W12O40(8−n)−, from Al3+ to Si4+ to P5+. This results in a stepwise and linear modulation of ion charge and reduction potential, whose concerted effects on reaction rates can be used to better understand electron‐transfer processes. Starting from the acquisition of activation parameters associated with electron self‐exchange between the POMs themselves, the studies discussed in this review provide a detailed account of electron transfer from reduced α‐Keggin heteropolytungstate anions to dioxygen, culminating in the recent discovery of a fundamentally new mechanism for electron transfer to O2 in water.

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Electrochemistry and Homogeneous Self-Exchange Kinetics of the Aqueous 12-Tungstoaluminate(5−/6−) Couple

Cited by 29 publications

References 55 publications

Electron Transfer Reactions

Electron Transfer Reactions

Ligand- and oxygen-isotope-exchange pathways of geochemical interest

The Reduction of Dioxygen by Keggin Heteropolytungstates

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