Borate Accelerates Rates of Steady Oxygen‐Isotope Exchange for Polyoxoniobate Ions in Water

Villa, Eric M.; Ohlin, C. André; Casey, William H.

doi:10.1002/chem.201000946

Cited by 18 publications

(14 citation statements)

References 21 publications

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“…Such metastable structures form through concerted movements of many atoms at nanometer-sized steps to establish an equilibrium, and often this process involves separation of charges in solution, which explains why even nominally inert counterions influence the rates of reaction, as we show here. [17] Our observations provide strong evidence for the importance and reality of such metastable intermediates.…”

Section: Angewandte Chemiementioning

confidence: 54%

Dynamics of a Nanometer‐Sized Uranyl Cluster in Solution

et al. 2013

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A class of uranyl peroxide clusters was discovered before as nanometer-sized ions that form spontaneously in aqueous solutions. The uranyl(VI) cluster investigated here is approximately 2 nm in diameter, contains 24 uranyl moieties, and 12 pyrophosphate units. NMR spectroscopy shows that the ion has two distinct forms that interconvert in milliseconds to seconds depending on the temperature and the size of the counterions. P blue, O red, U yellow.

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Section: Angewandte Chemiementioning

confidence: 54%

Dynamics of a Nanometer‐Sized Uranyl Cluster in Solution

et al. 2013

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“…As in the case for the MAl 12 molecules, there is an inert oxygen site in the molecule that tells one when the molecule dissociates fully -it is a central m 6 -O with a sharp and distinct 17 O NMR signal [96][97][98][99][100][101] and, when the signal for this oxygen diminishes, it is clear that the molecule is dissociating. Slow diminution of the 17 O NMR signal for the central m 6 -O site unequivocally indicates that the decaniobate ion is slowly dissociating.…”

Section: Rate Of Dissociationmentioning

confidence: 74%

“…Counterion choice also effects the oxygen-isotope exchange rates regiospecifically, [98] although we do not illustrate these effects with a figure. Also, the local effect on site reactivities of the Ti IV substitution is surprisingly small -approximately a factor of two.…”

Section: Rate Of Dissociationmentioning

confidence: 90%

“…The decaniobate [H x Nb 10 O 28 ] (6Àx)À ion (Fig. 1, bottom) has seven structurally distinct oxygens in D 2v symmetry that react so slowly that oxygen-isotope exchanges can be followed at each site using 17 O NMR spectroscopy [96][97][98][99][100][101] 17 O so that decreases in the 17 O NMR signal from each structural oxygen can be used to gauge rates of isotopic equilibration of that oxygen apart from all others in the structure.…”

Section: Rate Of Dissociationmentioning

confidence: 99%

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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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“…While V, Mo, and W mainly exist as monomeric oxide ions at pH > 9, several examples of polyoxoniobates and -tantalates which are stable to pH > 13 are known. [3][4][5] Polyoxometalates possess several attractive features, as they resemble small fragments of minerals in terms of structural features. [6] The high oxidation state of the metals in the oxide framework has also suggested their use either as catalysts or ligands [7] in oxidative chemistry, such as water oxidation.…”

Section: Polyoxometalatesmentioning

confidence: 99%

Reaction Dynamics and Solution Chemistry of Polyoxometalates by Electrospray Ionization Mass Spectrometry

Ohlin

2011

Chemistry An Asian Journal

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Mass spectrometry both complements other analytical techniques and allows for types of analyses and experiments not possible with common analytical methods, such as NMR, IR, and UV/Vis spectroscopy. Electrospray constitutes one of the mildest forms of ionization, making it the preferred method for the analysis of large fragile or reactive ions. There is particular promise for mass spectrometry in aiding the characterization of polyoxometalates and their solutions, but caution must be taken in designing the experiments in order to yield reliable data and to avoid the temptation of over-interpreting the relevance of gas-phase data to solution chemistry.

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Borate Accelerates Rates of Steady Oxygen‐Isotope Exchange for Polyoxoniobate Ions in Water

Cited by 18 publications

References 21 publications

Dynamics of a Nanometer‐Sized Uranyl Cluster in Solution

Dynamics of a Nanometer‐Sized Uranyl Cluster in Solution

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

Reaction Dynamics and Solution Chemistry of Polyoxometalates by Electrospray Ionization Mass Spectrometry

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