Study on crystallographically inequivalent protons in RbH2AsO4 using static NMR and MAS NMR

• Spin–lattice relaxation times in laboratory frame and in rotating frame.
• Dynamics of two distinct hydrogen bonds, H(1) and H(2), in RbH2AsO4.
• Reorientational motion for H(1) in RbH2AsO4.

Two inequivalent protons from 1H NMR spectra of RbH2AsO4 in the paraelectric phase were distinguished using static NMR and MAS NMR. From the 1H spin–lattice relaxation times in the laboratory frame, T1, and rotating frame, T1ρ, of the two crystallographically inequivalent hydrogen sites, i.e., H(1) and H(2), the temperature dependences of T1 and T1ρ for H(1) were related to the reorientational motion. The shorter H(1) bonds give rise to stronger H-bonds, and protons involved in stronger H-bonds have long relaxation times. Consequently, the RbH2AsO4 structure has two crystallographically inequivalent sites with two different hydrogen-bond lengths.

Figure optionsDownload as PowerPoint slide