Solid-state NMR investigation of the novel microporous gallophosphate cloverite

Abstract

The investigation of the gallophosphate molecular sieve cloverite by solid-state 13C, 31P, and 71Ga NMR techniques is described. Comparison of the 13C CP/MAS spectra of cloverite quinuclidine and quinuclidinium chloride give further evidence that the templating amine is protonated. The non-spinning CP experiment shows the full chemical shift anisotropy and reveals no motion of the template molecules. The 1H-decoupled 31P MAS spectrum of cloverite exhibits very poor resolution. However, the resonance lines of the five crystallographically independent 31P atoms are resolved by applying a dipolar-dephasing technique which utilizes differences in dipolar 31P—1H interactions. CP/MAS experiments with variable contact times and a depolarization experiment support this result and allow partial assignment of resonance lines to two groups of 31P atoms. The experimental conditions for 71Ga CP/MAS experiments were evaluated using Ga2(SO4)3·18H2O as a model substance. Application to cloverite with decreasing contact times shifts the maximum of the main signal from − 41 to − 26 ppm, thus indicating the presence of gallium sites with different cross-polarization dynamics.