A 69Ga and 71Ga MAS NMR study of the gallium analogue zeolite ZSM-5

69Ga and 71Ga magic-angle-spinning (MAS) NMR spectra of a series of gallium analogue zeolites H—(Ga)ZSM-5, with varying Si/Ga ratios, were obtained at 14.1 and 7.1 T. The quadrupole coupling constant e2qQ/h was deduced from the shift difference of the centre of gravity of the 69Ga and 71Ga resonance. An analysis of the linewidth as a function of the magnetic field shows that the width is not only determined by the second-order quadrupolar broadening, but also by a distribution of chemical shifts. The values obtained for the quadrupole coupling constant and chemical shift distribution are compared to those found for 27Al in H—(Al)ZSM-5. It is argued that the observed differences are related to the different NMR properties of the isotopes, and do not point to any structural changes of the ZSM-5 lattice.