Intriguing Role of a Quaternary Ammonium Cation in the Dissociation Chemistry of Keggin Polyoxometalate Anions

Abstract

The gas-phase fragmentations of a series of Keggin polyoxometalate anions with molecular formula of TBA n [XM 12 O 40 ] (X = P, Si; M = Mo, W) were studied by electrospray ionization tandem mass spectrometry. of the ion clusters in the gas phase, which was in excellent agreement with the relative orders of thermal stability in the condensed phase.

Cation-Anion Interactions and Synergistic Catalysis by Supramolecular Polyoxometalate Complexes [C10H18N]n[XM12O40]

“…The proton‐transfer reaction was supposed to be driven by the strong tendency to abstract proton(s) onto the bridging oxygen atoms of POM framework, thus remarkably reducing the net charges of the anion. This observation is surprisingly consistent with the fragmentations of NR 4 + ‐bound complexes {NR 4 [POM]} (n−1)− ,, in which the secondary dissociation of the primary product {R[POM]} (n−1)– led to {H[POM]} (n−1)− and neutral alkenes C n H 2n (R=C n H 2n+1 ). Unlike the quaternary ammonium salts of POMs, no cation‐adducted anions {(C 10 H 18 N) m [XM 12 O 40 ]} (n−m)− were found, suggesting that the bulky [C 10 H 18 N] + cation shows a weaker interaction with POMs than [NR 4 ] + does although it is the strongest Lewis acid among the ammonium ions in the study.…”

“…The organic amines chosen for the study were those frequently used in the “shrink‐wrapping” approach. This is a continuation of our previous fragmentation study on the quaternary ammonium salts of POMs with Keggin, Dawson and Lindqvist structures by ESI‐MS , …”

Can polyoxometalates enhance the capacitance and energy density of activated carbon in organic electrolyte supercapacitors?

“…It should be stressed that protons are crucial in aqueous electrolytes for keeping the overall charge of the POM clusters at a low 3-/4-by concomitant protonation during reduction. Thus, in the absence of protons in the present organic electrolytes, we consider that the TEA counterions must fulfill a similar role most likely through the formation of ion pairs, as it has been previously reported in other organic solvents with a variety of cations [37][38][39]. Furthermore, we postulate that due to the absence of protons in the organic electrolyte and the formation of ion pairs with the TEA cations, the most negative pH-dependent redox wave has split in two.…”

Complex solution chemistry behind the simple “one‐pot” synthesis of vanadium‐substituted polyoxometalates unraveled by electrospray ionization mass spectrometry

“…[14][15][16][17][18] The power of ESI-MS relies on the 4S characteristics (speed, sensitivity, specialty, and stoichiometry) summarized by McLafferty, [19] which enables MS suitable for monitoring the dynamic speciation changes that occur in the reaction solution and detecting the low-abundance, transient reaction intermediates. [20] We have used this technique to characterize a range of POMs with saturated and lacunary structures, [21][22][23][24] to study the synergetic catalysis, resulting from the specific cation-anion interaction, [25] and to probe the formation mechanism of sandwich-type POMs using [γ-SiW 10 O 36 ] 8À ({γ-SiW 10 }) as a starting material by combining ESI-MS and X-ray crystallography. [26] Herein, we present the first systematic ESI-MS investigation to show how the reaction conditions such as concentration, temperature, molar ratios, and reaction time can sensitively change the solution speciation and hence the final product via taking the binary reaction of Keggin-type lacunary silicotungstates ([SiW 11 O 39 ] 8À , [SiW 10 O 36 ] 8À , [SiW 9 O 34 ] 10À , abbreviated as {SiW 12Àx }, x = 1, 2, and 3) with vanadium salts (NaVO 3 ) as an example.…”