Solid-state 33S MAS NMR of inorganic sulfates.

Solid-state (33)S MAS NMR spectra of a variety of inorganic sulfates have been obtained at magnetic field strengths of 4.7, 14.1, 17.6, and 18.8 T. Some of the difficulties associated with obtaining natural abundance (33)S NMR spectra have been overcome by using a high magnetic field strength and magic angle spinning (MAS). Multiple factors were considered when analyzing the spectral linewidths, including magnetic field inhomogeneity, dipolar coupling, chemical shift anisotropy, chemical shift dispersion, and quadrupolar coupling. In most of these sulfate samples, quadrupolar coupling was the dominant line broadening mechanism. Nuclear electric quadrupolar coupling constants (C(q)) as large as 2.05 MHz were calculated using spectral simulation software. Spectral information from these new data are compared with X-ray measurements and GAUSSIAN 98W calculations. A general correlation was observed between the magnitude of the C(q) and the increasing difference between S-O bond distances within the sulfate groups. Solid-state (33)S spin-lattice (T(1)) relaxation times were measured and show a significant reduction in T(1) for the hydrated sulfates. This is most likely the result of the modulation of the time-dependent electric field gradient at the nuclear site by motion of water molecules. This information will be useful in future efforts to use (33)S NMR in the compositional and structural analysis of sulfur containing materials.

Solid state 33S NMR of inorganic sulfides.

Solid state 33S NMR spectra of a variety of inorganic sulfides have been obtained at magnetic field strengths of 4.7 and 17.6T. Spectra acquired with magic angle spinning show considerable improvements in sensitivity and resolution when compared with static spectra. Multiple factors are considered when analyzing the spectral line widths, including; magnetic field inhomogeneity, dipolar coupling, chemical shift anisotropy, chemical shift dispersion (CSD), T(2) relaxation, and quadrupolar coupling. Quadrupolar coupling was expected to be the dominant line broadening mechanism. However, for most of the samples CSD was the prevailing line broadening mechanism. Thus, for many of the metal sulfides studied at a high magnetic field strength, the line widths were actually larger than those observed in the spectra at low field. This is atypical in solid state 33S NMR. Solid state 33S spin-lattice (T(1)) and spin-spin (T(2)) relaxation rates were measured for the first time and are discussed. This information will be useful in future efforts to use 33S NMR in the compositional and structural analysis of sulfur containing materials.