Probing the Self-Assembly of Inorganic Cluster Architectures in Solution with Cryospray Mass Spectrometry: Growth of Polyoxomolybdate Clusters and Polymers Mediated by Silver(I) Ions

• Published in: Journal of the American Chemical Society 2008-10, Vol.130 (42), p.13876-13884
• Main Authors: Wilson, Elizabeth F, Abbas, Hamera, Duncombe, Bridgette J, Streb, Carsten, Long, De-Liang, Cronin, Leroy
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja802514q

Cryospray mass spectrometry (CSI-MS) has been used to probe the mechanism of self-assembly of polyoxometalate clusters in solution. By using CSI-MS and electronic absorbance spectroscopy it was possible to monitor in real-time the self-assembly of polymeric chains based on [Ag2Mo8O26]2− n building blocks. The role of the AgI ion in the solution state rearrangement of molybdenum Lindqvist ({Mo6}) into the silver-linked β-octamolybdate ({Mo8}) structure ((n-C4H9)4N)2n [Ag2Mo8O26] n (1) is revealed in unprecedented detail. A monoanionic series, in particular [AgMo m O3m+1]− where m = 2 to 4, and series involving mixed oxidation state polyoxomolybdate species, which illustrate the in-solution formation of the (Ag{Mo8}Ag) building blocks, have been observed. CSI-MS detection of species with increasing metal nuclearity concomitant with increasing organic cation contribution supports the hypothesis that the organic cations used in the synthesis play an important structure-directing role in polyoxometalate (POM) growth in solution. A real-time decrease in [{Mo6}] and associated increase in [{Mo8}] have been observed using CSI-MS and electronic absorbance spectroscopy, and the rate of {Mo6} interconversion to {Mo8} was found to decrease on increasing the size of the countercation. This result can be attributed to the steric bulk of larger organic groups hindering {Mo6} to {Mo8} rearrangement and hindering the contact between silver cations and molybdenum anions.