Definitive solid-state 185/187Re NMR spectral evidence for and analysis of the origin of high-order quadrupole-induced effects for I = 5/2

Abstract

Rhenium-185/187 solid-state nuclear magnetic resonance (SSNMR) experiments using NaReO₄ and NH₄ReO₄ powders provide unambiguous evidence for the existence of high-order quadrupole-induced effects (HOQIE) in SSNMR spectra. Fine structure, not predicted by second-order perturbation theory, has been observed in the ^185/187Re SSNMR spectrum of NaReO₄ at 11.75 T, where the ratio of the Larmor frequency (ν₀) to the quadrupole frequency (ν_Q) is ∼2.6. This is the first experimental observation that under static conditions, HOQIE can directly manifest in SSNMR powder patterns as additional fine structure. Using NMR simulation software which includes the quadrupole interaction (QI) exactly, extremely large ^185/187Re nuclear quadrupole coupling constants (C_Q) are accurately determined. QI parameters are confirmed independently using solid-state ^185/187Re nuclear quadrupole resonance (NQR). We explain the spectral origin of the HOQIE and provide general guidelines that may be used to assess when HOQIE may impact the interpretation of the SSNMR powder pattern of any spin-5/2 nucleus in a large, axially symmetric electric field gradient (EFG). We also quantify the errors incurred when modeling SSNMR spectra for any spin-5/2 nucleus within an axial EFG using second-order perturbation theory. Lastly, we measure rhenium chemical shifts in the solid state for the first time.