Long Hydrogen-Bonded Rod of Molecular Oxide: A Hexatantalate Tetramer

Matsumoto, Miki; Ozawa, Yoshiki; Yagasaki, Atsushi

doi:10.1021/ic3004883

Cited by 31 publications

(14 citation statements)

References 32 publications

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“…15 Decatantalate, [Ta 10 O 28 ] 6− has been very recently isolated as a tetrabutylammonium (TBA) salt from nonaqueous solution, 16 and similar chemistry was also employed to obtain TBA salts of [H 2 Ta 6 O 19 ] 6− . 17,18 Even the protonated [H 2 Ta 6 O 19 ] 6− clusters were a noteworthy discovery, as identification of the most basic oxo ligand of the hexatantalate cluster was under some debate. 15,17,19 However, unlike Nb-POM chemistry, no additional heteropolyanions, or lacunary derivatives have been observed or isolated.…”

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confidence: 99%

Contrasting ion-association behaviour of Ta and Nb polyoxometalates

et al. 2014

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Small-angle X-ray scattering (SAXS) studies of aqueous [Ta6O19](8-) compared to prior studies of aqueous [Nb6O19](8-) reveals key differences in behaviour, which is likely at the root of the difficultly in developing polyoxotantalate chemistry. Specifically, where contact ion-pairing dominates between [Nb6O19](8-) and its counterions, solvent-separated ion-pairing between [Ta6O19](8-) and its counterions has been unveiled in the current study.

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confidence: 99%

Contrasting ion-association behaviour of Ta and Nb polyoxometalates

et al. 2014

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“…Like the high-temperature calorimetry, this too indicates that Ta

is `less selective’ in its ion association than Nb

(in both solution and solid state). On the other hand, it has been noted that Nb

is more basic than Ta

, meaning it protonates upon dissolution in water, at the bridging oxos sites [ 32 , 33 ]. Since protonation is an endothermic process that is not equal between the Ta

and Nb

, it is difficult to compare the dissolution enthalpy with exact certainty.…”

Section: Resultsmentioning

confidence: 99%

Thermochemical Measurements of Alkali Cation Association to Hexatantalate

et al. 2018

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Ion association is an important process in aqueous dissolution, precipitation, and crystallization of ionic inorganic, organic, and biological materials. Polyoxometalates (POMs) are good model compounds for understanding the complex relationships between lattice energy, ion-pairing in solution, and salt solubility. Here we perform calorimetric measurements to elucidate trends in cluster stability, lattice energy, and ion-pairing behavior studies of simple hexatantalate salts in neat water, parent hydroxide solutions, and molybdate melts, extending previous studies on the isostructural hexaniobates. High temperature calorimetry of alkali salts of hexatantalate reveals that the enthalpies of formation from oxides of the K, Rb, and Cs salts are more similar to each other than they are for their niobate analogues and that the tantalate cluster is energetically less stable than hexaniobate. Aqueous dissolution calorimetry reveals that the cesium salt of hexatantalate has a similar concentration dependence on its dissolution enthalpy to that of hexaniobate. However, unlike rubidium hexaniobate, rubidium hexatantalate also exhibits increased concentration dependence, indicating that hextantalate can undergo increased ion-pairing with alkali salts other than cesium, despite the dilute environments studied. Dissolution enthalpies of POM salts in the parent alkali hydroxides shows that protonation of clusters stabilizes lattices even more than the strongly associating heavy alkali cations do. Additionally, neither weak nor strong lattice ion associations necessarily correlates with respectively high or low aqueous solubility. These studies illuminate the importance of considering ion-pairing among the interrelated processes in the aqueous dissolution of ionic salts that can be extended to serving as a model of cation association to metal oxide surfaces.

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“…Like the high-temperature calorimetry, this too indicates that Ta 6 is 'less selective' in its ion association than Nb 6 (in both solution and solid state). On the other hand, it has been noted that Nb 6 is more basic than Ta 6 , meaning it protonates upon dissolution in water, at the bridging oxos sites [32,33]. Since protonation is an endothermic process that is not equal between the Ta 6 and Nb 6 , it is difficult to compare the dissolution enthalpy with exact certainty.…”

Section: Dissolution Energy Of Ta 6 Saltsmentioning

confidence: 99%

Thermochemical Measurements of Alkali Cation Association to Hexatantalate

Sures¹,

Nagabhushana²,

Navrotsky³

et al. 2018

Preprint

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Ion association is an important process in aqueous dissolution, precipitation, and~crystallization of ionic inorganic, organic, and biological materials. Polyoxometalates (POMs) are good model compounds for understanding the complex relationships between lattice energy, ion-pairing in solution, and salt solubility. Here we perform calorimetric measurements to elucidate trends in cluster stability, lattice energy, and ion-pairing behavior studies of simple hexatantalate salts in neat water, parent hydroxide solutions, and molybdate melts, extending previous studies on the isostructural hexaniobates. High temperature calorimetry of alkali salts of hexatantalate reveals that the enthalpies of formation from oxides of the K, Rb, and Cs salts are more similar to each other than they are for their niobate analogues and that the tantalate cluster is energetically less stable than hexaniobate. Aqueous dissolution calorimetry reveals that the cesium salt of hexatantalate has a similar concentration dependence on its dissolution enthalpy to that of hexaniobate. However, unlike~rubidium hexaniobate, rubidium hexatantalate also exhibits increased concentration dependence, indicating that hextantalate can undergo increased ion-pairing with alkali salts other than cesium, despite the dilute environments studied. Dissolution enthalpies of POM salts in the parent alkali hydroxides shows that protonation of clusters stabilizes lattices even more than the strongly associating heavy alkali cations do. Additionally, neither weak nor strong lattice ion associations necessarily correlates with respectively high or low aqueous solubility. These studies illuminate the importance of considering ion-pairing among the interrelated processes in the aqueous dissolution of ionic salts that can be extended to serving as a model of cation association to metal oxide surfaces.

show abstract

Long Hydrogen-Bonded Rod of Molecular Oxide: A Hexatantalate Tetramer

Cited by 31 publications

References 32 publications

Contrasting ion-association behaviour of Ta and Nb polyoxometalates

Contrasting ion-association behaviour of Ta and Nb polyoxometalates

Thermochemical Measurements of Alkali Cation Association to Hexatantalate

Thermochemical Measurements of Alkali Cation Association to Hexatantalate

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