Electric field gradient distributions about strontium nuclei in cubic and octahedrally symmetric crystal systems

Abstract

Strontium nuclei $(^{87}\mathrm{Sr})$ in natural abundance are examined with magic angle spinning (MAS) nuclear magnetic resonance (NMR) of powder samples possessing either simple cubic (SrO) or fluorite-analogue (${\mathrm{SrCl}}_{2}$ and ${\mathrm{SrF}}_{2}$) structures. The MAS spectra of these samples reveal a sideband pattern resulting from first order quadrupolar broadening of the outer transitions brought about by imperfections in the crystal structure. These imperfections lead to a distribution of electric field gradients (efgs) that can be characterized in these cases by fitting integrated sideband intensities as a function of spectral frequency with a Lorentzian function. Strontium oxide is simple cubic and found to have an isotropic $^{87}\mathrm{Sr}$ chemical shift of $340\ifmmode\pm\else\textpm\fi{}1\phantom{\rule{0.3em}{0ex}}\mathrm{ppm}$ with respect to 1 M ${\mathrm{SrCl}}_{2}$ (aqueous) and an efg distribution with a full width at half-height (FWHH) of $50.4\ifmmode\pm\else\textpm\fi{}2.5\phantom{\rule{0.3em}{0ex}}\mathrm{kHz}$. Strontium chloride (anhydrous) is isostructural with fluorite and was found to have a $^{87}\mathrm{Sr}$ chemical shift of $45.9\ifmmode\pm\else\textpm\fi{}1.2\phantom{\rule{0.3em}{0ex}}\mathrm{ppm}$ and an efg distribution with a FWHH of $30.9\ifmmode\pm\else\textpm\fi{}1.4\phantom{\rule{0.3em}{0ex}}\mathrm{kHz}$. Strontium fluoride is also isostructural with fluorite and had a $^{87}\mathrm{Sr}$ chemical shift of $\ensuremath{-}13.0\ifmmode\pm\else\textpm\fi{}1.2\phantom{\rule{0.3em}{0ex}}\mathrm{ppm}$ and an efg FWHH of $104\ifmmode\pm\else\textpm\fi{}18\phantom{\rule{0.3em}{0ex}}\mathrm{kHz}$.