Electrospray Behavior of Lacunary Keggin‐Type Polyoxotungstates [XW₁₁O₃₉]^p− (X = Si, P): Mass Spectrometric Evidence for a Concentration‐Dependent Incorporation of an MOⁿ⁺ (M = W^VI, Mo^VI, V^V) Unit into the Polyoxometalate Vacancy

Abstract

ESI-MS analysis provides a straightforward tool for the solution characterization of highly charged mono-lacunary Keggin-type polyoxotungstates α- [XW 11 O 39 ] p− (X = Si, P; p = 8, 7). Doubly and triply charged quasi-molecular ion peaks were identified on the basis of both the theoretical simulation of the isotopic cluster distributions and the fragmentation modes observed with MS/MS technique. This approach allows the characterization of the inorganic polyanions transferred into the gas-phase with associated alkali metal cations (Li + , Na + ). Indeed, the ESI-MS spectrum was found to be dependent on the counterion nature and on the initial concen-

Electrospray ionization mass spectrometry of a cerium(III) phosphomolybdate complex: Condensed and gas-phase cluster chemistry

“…An example of this effect is the protonation of surface oxygens and subsequent loss of neutral H 2 O molecules from lacunary Keggin ions, e.g., PMo 11 O 39 7− + 4H + → PMo 11 O 37 3− + 2H 2 O, which has been shown to be an effective method of reducing the charge of these POM ligands during the spray process [9]. Intriguing concentration-dependent behavior has also been reported by Bon [10]. The inherent electrochemistry of ESI can be used, for example, to employ the different redox properties of nickel and cobalt porphyrins for their independent detection from solution mixtures [13].…”

“…(9a)-(9c), as well as other gas-phase processes, can be excluded as feasible explanations. It is therefore concluded that the precursor of Ce(III)PMo 10 26 2− , which increase in relative abundance across the series. A detailed understanding of these variations in ESI/MS spectra is beyond the scope of this work.…”

“…The complex behavior of iso-and heteropolyoxometalates during transference from solution to gas has been determined from investigations via electrospray ionization mass spectrometry (ESI/MS) [2][3][4][5][6][7][8][9][10][11]. ESI, while a "soft" process in principle, has the potential to cause structural and chemical transformations of solution species during ion formation and transport.…”

Oxygenation by Ruthenium Monosubstituted Polyoxotungstates in Aqueous Solution: Experimental and Computational Dissection of a Ru(III)–Ru(V) Catalytic Cycle

“…[61,62] The m/z value and the isotopic signature pertaining to the multimetal polyanionic cluster provide direct evidence of the POM solution speciation (Figure 1 (Figure 2). This feature can be associated to the higher negative charge of the undecatungstosilicate ligand with respect to the tungstophosphate analogue, favoring the oneelectron oxidation of the Ru II and its evolution to the Ru III species under the adopted synthetic conditions.…”

Electrospray Ionization Based Methods for the Generation of Polynuclear Oxo- and Hydroxo Group 6 Anions in the Gas-Phase

“…ESI is a soft ionisation technique that permits transfer of ions from condensed-phases to the gas-phase with minimal fragmentation and has been shown to be a convenient tool for the characterization of high nuclearity group 6 polyoxyanions and for the study of their aqueous speciation under a wide pH range. [27][28][29][30][31][32] Typically, ESI generation of gaseous anions with M=O or M-OH groups heavily relies on the availability of preexisting polynuclear entities in solution, a fact that for example precludes the production of the elusive [W 2 O 7 ] 2-dianion or tri-tetra-and pentanuclear group 6 oxide species in the gas-phase.…”