Proton dynamics in the room-temperature phase of Cs3(HSO4)2(H2PO4) studied by 1H MAS NMR

Abstract Proton dynamics in the room-temperature phase of Cs 3 (HSO 4 ) 2 (H 2 PO 4 ) has been studied by means of 1 H magic-angle-spinning (MAS) NMR. The 1 H MAS NMR spectra show the presence of several inequivalent proton sites, and their line shapes are dependent on temperature. 1 H signals are assigned by the use of the correlation between the 1 H chemical shift and the hydrogen bond strength, which are supported by 1 H MAS NMR experiments cross-polarized from 31 P. The signal coalescence caused by the SO 4 reorientation takes place at 310 K, while the coalescence caused by the PO 4 reorientation takes place at 330 K. Consequently, the SO 4 reorientation is a little bit faster than the PO 4 reorientation at a given temperature. The 1 H chemical shifts demonstrate that the PO 4 tetrahedra are connected by the stronger hydrogen bonds than the SO 4 tetrahedra are. Thus, the hydrogen bond strength controls the SO 4 /PO 4 reorientation.