Electrospray mass spectrometry of aqueous solutions of isopolyoxotungstates

Electrospray mass spectrometry (ESMS) has been conducted on aqueous solutio ns of isopolyoxotungstate systems. There is direct evidence that the desorp tion process in the ESMS technique has resulted in significant chemical eff ects, resulting in the detection of many new anions and cations. For the am monium polyoxotungstate system, negative-ion ESMS yields ions of the form [ HWmO3m+1](-), [WmO3m+1](2-), and [HWmO3m+2](3-) (with the latter being bett er formulated as [H2W2mO6m+4](6-)). For the alkali metal polyoxotungstate s ystems ions of the form [W(m)O(3m+1)A](-) and [W(m)O(4m)A(2m-2)](2-) (where A = Li+, Na+, K+) were observed. For positive-ion ESMS two series were obs erved, namely, the [W(m)O(4m)A(2m+1)](+) and [W(m)O(4m)A(2m+2)](2+) ions. I n the ammonium polyoxotungstate system, aggregates of both the [HWmO3m+1](- ) and the [WmO3m+1](2-) series can be classified as open-chained structures of tetrahedra that are cooler shared, whereas the more highly charged anio ns [H2W2mO6m+4](6-) are consistent with closed-packed structures which are based on the structure of paratungstate-B [H2W12O42](10-). For the alkali m etal tungstate systems, the ESMS spectra are consistent with open-chained s tructures of octahedral units that are edge shared, with a terminating tetr ahedral unit. Linear correlations suggest that the assembly of these aggreg ates occurs via an additive polymerization mechanism for which the additive moieties (WO3, WO22+, and W(2)O(8)A(4)) in aqueous solution can be identif ied.