Journal of Physical Chemistry B, Vol.103, No.29, 5920-5927, 1999
H-2-{H-1} CPMAS NMR of guest-host species in zeolites: An experimental study
The feasibility of H-2-{H-1} cross-polarization magic-angle spinning (CPMAS) NMR and its implementation in HETCOR experiments is studied using as-made all-silica zeolites. The results presented show that H-2-{H-1} CPMAS can be employed successfully in two-dimensional correlation spectroscopy experiments. The effects of experimental and physical parameters (spin rate, RF field strengths, H-1 homonuclear dipole-dipole coupling, and the magnitude of the quadrupole coupling constants) on the NMR spectra are studied in detail. In the limit of small quadrupole coupling constants and weak proton homonuclear dipolar coupling, the crosspolarization behavior of the deuterons is similar to spin I = 1/2 systems and proton spin-diffusion is minimal. Samples with larger quadrupole coupling constants and strong proton dipole-dipole coupling exhibit less efficient spin-locking of the deuterons and proton spin-diffusion is more prevalent. In this case, it is necessary to perform proton spin-diffusion experiments in conjunction with the correlation spectroscopy. Minimizing proton spin-diffusion is crucial for correct interpretation sf the multidimensional correlation spectroscopy experiments, which can be achieved for the samples studied here by using short contact times. H-2-{H-1} CPMAS HETCOR experiments could find uses for bath organic and organic-inorganic solids where selective deuteration can be achieved.