¹⁸⁵Re and ¹⁸⁷Re solid‐state NMR of metaperrhenates

Abstract

I solid-state NMR investigations of specific metaperiodates with alkyl-or aryl-substituted cations of main Group V revealed second-order quadrupole effects, except in the case of tetraethylammonium and tetramethylphosphonium metaperiodate. In these compounds the lZ7I quadrupole interactions are either very small or vanish. This allowed the approximate evaluation of the electric field gradients of the analogous isomorphous metaperrhenates. Despite the very large nuclear quadrupole moments of the rhenium isotopes, the estimated values of the ' "Re and Is7Re quadrupole coupling constants of tetraethylammonium and tetramethylphosphonium metaperrhenate have an order of magnitude accessible to solid-state NMR measurements. The ' ' ' Re and lS7Re NMR powder spectra of rhenium compounds in non-cubic lattice structures were measured for the first time. The complete ' "Re and lS7Re solid-state NMR spectra of polycrystalline tetramethylphosphonium metaperrhenate were observed, showing temperaturedependent second-order quadrupole splittings. In this compound the ReO; anions show very small deviations from tetrahedral symmetry, which were estimated from a point charge model and the measured quadrupole splittings. In contrast, the tetrahedral symmetry of the ReO; ions of tetraethylammonium metaperrhenate is nearly undistorted, because no quadrupole splittings of the ' ' ' Re and lS7Re signals were detectable in the powder NMR spectrum.

Dynamic Effects on the Powder Line Shapes of Half-Integer Quadrupolar Nuclei: A Solid-State NMR Study of XO4- Groups

“…23 Because of this feature little solid NMR data is available about these nuclei, all of them arising from highly symmetric substitution environments. [24][25][26] In the present work, static powder 185/187 Re NMR spectra were acquired on NH 4 ReO 4 , NaReO 4 , and AsPh 4 ReO 4 samples that were kindly provided to us by Prof. C. Barnes (University of Tennessee). These Re NMR spectra were acquired using protocols that have been recently described for collecting meaningful wide-line central transition data in the strong coupling regime.…”

“…), possessing some of the largest nuclear quadrupole moments in the Periodic Table (2.4 barn for 185 Re, 2.2 barn for 187 Re) − In the present work, static powder 185/187 Re NMR spectra were acquired on NH 4 ReO 4 , NaReO 4 , and AsPh 4 ReO 4 samples that were kindly provided to us by Prof. C. Barnes (University of Tennessee). These Re NMR spectra were acquired using protocols that have been recently described for collecting meaningful wide-line central transition data in the strong coupling regime. , These methods include suitably timed spin−echoes to overcome the effects of the spectrometer dead time, short pulse lengths and relatively weak Rf fields to maximize homogeneity in the excitation, and the co-addition of purely absorptive frequency-domain spectra acquired as a function of the transmitter irradiation offset.…”

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

“…In addition, they possess relatively high magnetogyric ratios (g( 185 Re) = 6.1057 Â 10 7 rad s À1 T À1 ; g( 187 Re) = 6.1682 Â 10 7 rad s À1 T À1 ). 10 Despite the potential wealth of diagnostic information that could be extracted using 185/187 Re SSNMR experiments, very few literature reports exist, and they are nearly exclusively restricted to compounds that exhibit very high symmetry, [11][12][13] or are from experiments carried out at liquid helium temperatures. [14][15][16] The paucity of 185/187 Re SSNMR studies may be attributed to the very large Q for both NMR-active nuclides (Q( 185 Re) = 2180 (20) mb; Q( 187 Re) = 2070(20) mb).…”

Solid-state185/187Re NMR and GIPAW DFT study of perrhenates and Re2(CO)10: chemical shift anisotropy, NMR crystallography, and a metal–metal bond

“…70 However, very few literature reports of 185/187 Re SSNMR exist, and they are primarily restricted to very high symmetry rhenium environments and/or low temperature conditions. [71][72][73][74][75][76][77][78][79][80] The dearth of 185/187 Re SSNMR information is attributed to the very large Q for both NMR-active nuclides (Q( 185 Re) = 2180 (20) mb; Q( 187 Re) = 2070(20) mb). 81 As such, a very small EFG can result in a rhenium QI that broadens the SSNMR powder pattern to the point that it is undetectable.…”