Proton dynamics in the room-temperature phase of Cs3(HSO4)2(H2PO4) was studied by means of 1H magic-angle-spinning nuclear magnetic resonance. The 1H magic-angle-spinning nuclear magnetic resonance spectra show the presence of several inequivalent proton sites, and their line shapes were dependent on temperature. 1H signals were attributed by the use of the correlation between the 1H chemical shift and the H bond strength, which were supported by 1H magic-angle-spinning nuclear magnetic resonance experiments cross-polarized from 31P. The signal coalescence caused by the SO4 reorientation takes place at 310K, while the coalescence caused by the PO4 reorientation takes place at 330K. Consequently, the SO4 reorientation was a little bit faster than the PO4 reorientation at a given temperature. The 1H chemical shifts demonstrate that the PO4 tetrahedra were connected by the stronger H bonds than the SO4 tetrahedra are. Thus, the H bond strength controls the SO4/PO4 reorientation.

Proton Dynamics in the Room-Temperature Phase of Cs3(HSO4)2(H2PO4) Studied by 1H MAS NMR. H.Omi, K.Suzuki, S.Hayashi: Solid State Ionics, 2007, 178[27-28], 1493-8