Proton dynamics in the room-temperature phase of Cs 3(HSO 4) 2(H 2PO 4) studied by 1H MAS NMR

Abstract

Proton dynamics in the room-temperature phase of Cs 3(HSO 4) 2(H 2PO 4) has been studied by means of 1H magic-angle-spinning (MAS) NMR. The 1H MAS NMR spectra show the presence of several inequivalent proton sites, and their line shapes are dependent on temperature. 1H signals are assigned by the use of the correlation between the 1H chemical shift and the hydrogen bond strength, which are supported by 1H MAS NMR experiments cross-polarized from 31P. 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 1H 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.