Free Protons in Solid Heteropoly Compounds
Reference work entry
The basic structure of hetropoly acid hydrates (HPAs∙nH 2O) has already been determined by Keggin ( 1934), but the water and hydrated proton entities filing the channels (secondary structure) have not been studied much until the early 1990s. As heteropoly acids are superionic proton conductors at room temperature and good catalysts, it is clear that their activities will be the function of hydration degree and dynamics of proton species. Therefore, it was necessary to focus on the studies that identify protonic entities and follow their dynamics. The studies started on WPA-6, the most stable hydrate of WPA with well-known structure. Crystallographic results for WPA-6 show that Keggin’s anions in WPA-6 are stabilized by dioxonium ion H 5O 2 +, which was defined as planar and rigid (Brown et al. 1970). On the other hand, IR and Raman spectra taken at room temperature have shown that different protonic species (H 5O 2 +, H 3O +, H 2O) exist in dynamic equilibrium (Mioč et al. 1991, 2005; Colomban...
- Brown GN, Noe-Spirlet MR, Busing WR, Levy HA (1970) Dodecatungstophosphoric acid hexahydrate, (H5O2+)3(PW12O403–). The true structure of Keggin’s ‘pentahydrate’ from single–crystal x–ray and neutron diffraction data. Acta Cristalogr B33:1038–1045Google Scholar
- Kremenović A, Spasojević–de Birè A, Bourree F, Colomban P, Davidović M, Mioč UB (2002) Structural modifications of dodecatungstophosphoric acids hexahydrate induced by temperature in the 10–358 K range. In situ high–resolution neutron powder diffraction investigation. Solid State Ionics 150:431–442CrossRefGoogle Scholar
- Ratajczak HR, Barnes AJ, Bielanski A, Lutz HD, Müller A, Pope MT (2001) Polyoxometalate Chemistry from Topology via Self-Assembly to Applications. In: Pope MT, Müller A (eds) Kluwer, Dodrecht, pp 100–117Google Scholar
© Springer-Verlag Berlin Heidelberg 2016