Local environments and dynamics of hydrogen atoms in protonated forms of ion-exchangeable layered perovskites estimated by solid-state 1H NMR

The local environments and dynamics of hydrogen atoms in five samples of protonated forms of ion-exchangeable layered perovskites, Dion–Jacobson-type H[LaNb2O7] and H[LaTa2O7], Ruddlesden–Popper-type H2[SrTa2O7] and H2[La2Ti3O10], and H1.8[(Sr0.8Bi0.2)Ta2O7] derived from an Aurivillius phase, Bi2Sr2Ta2O9, have been investigated by solid-state 1H nuclear magnetic resonance spectroscopy (NMR). Solid-state 1H NMR with a magic-angle spinning technique conducted at room temperature reveals that the mean electron densities around the 1H nuclei in these protonated forms are relatively low, and that they decrease in the following order: H1.8[(Sr0.8Bi0.2)Ta2O7]>H[LaNb2O7]>H2[SrTa2O7]>H[LaTa2O7]>H2[La2Ti3O10]. The temperature-dependent solid-state 1H broad-line NMR spectra measured at 140–400 K reveal a decrease in the signal width for all of these five samples upon heating due to motional narrowing. The NMR spectra of H[LaNb2O7] and H[LaTa2O7] are different from the other three protonated forms due to the weaker dipole–dipole interactions at low temperatures and lower mobility of the hydrogen atoms at high temperatures.

Graphical abstractSolid-state 1H MAS NMR spectra of protonated forms of ion-exchangeable layered perovskites: (a) H[LaNb2O7]; (b) H[LaTa2O7]; (c) H1.8[(Sr0.8Bi0.2)Ta2O7]; (d) H2[SrTa2O7]; and (e) H2[La2Ti3O10]. The spinning side bands are marked with asterisks.Figure optionsDownload full-size imageDownload as PowerPoint slide