Experimental and theoretical investigations of the sulfite-based polyoxometalate cluster redox series: α - and β-[Mo18O54(SO3)2]4-/5-/6-

Baffert, C., Boas, J.F., Bond, A.M., Kögerler, P., Long, D.-L. , Pilbrow, J.R. and Cronin, L. (2006) Experimental and theoretical investigations of the sulfite-based polyoxometalate cluster redox series: α - and β-[Mo18O54(SO3)2]4-/5-/6-. Chemistry: A European Journal, 12(33), pp. 8472-8483. (doi:10.1002/chem.200501450)

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Publisher's URL: http://doi.wiley.com/10.1002/chem.200501450

Abstract

The synthesis, isolation and structural characterization of the sulfite polyoxomolybdate clusters α-(D3h)(C20H44N)4α-[Mo18O54(SO3)2]}CH3CN and β-(D3d)(C20H44N)4{β[Mo18O54(SO3)2]}CH3CN is presented. Voltammetric studies in acetonitrile (0.1 M Hx4NClO4, Hx4N=tetra-n-hexylammonium) reveal the presence of an extensive series of six one-electron reduction processes for both isomers. Under conditions of bulk electrolysis, the initial [Mo18O54(SO3)2]4-/5- and [Mo18O54(SO3)2]5-/6- processes produce stable [Mo18O54(SO3)2]5- and [Mo18O54(SO3)2]6- species, respectively, and the same reduced species may be produced by photochemical reduction. Spectroelectrochemical data imply that retention of structural form results upon reduction, so that both α and β isomers are available at each of the 4-, 5-, and 6-redox levels. However, the α isomer is the thermodynamically favored species in both the one- and two-electron-reduced states, with β-->α isomerization being detected in both cases on long time scales (days). EPR spectra also imply that increasing localization of the unpaired electron occurs over the α- and β-[Mo18O54(SO3)2]5- frameworks as the temperature approaches 2 K where the EPR spectra show orthorhombic symmetry with different g and hyperfine values for the α and β isomers. Theoretical studies support the observation that it is easier to reduce the α cluster than the β form and also provide insight into the driving force for β -->α isomerization in the reduced state. Data are compared with that obtained for the well studied α-[Mo18O54(SO4)2)]4- sulfate cluster.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Long, Dr Deliang and Cronin, Professor Lee
Authors: Baffert, C., Boas, J.F., Bond, A.M., Kögerler, P., Long, D.-L., Pilbrow, J.R., and Cronin, L.
Subjects:Q Science > QD Chemistry
College/School:College of Science and Engineering > School of Chemistry
University Centres > Glasgow Materials Research Initiative
Journal Name:Chemistry: A European Journal
Journal Abbr.:Chem. Eur J.
ISSN:0947-6539
ISSN (Online):1521-3765

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