Characterization of the Two Rubidium Sites in Rb₂CrO₄ by ⁸⁷Rb Single-Crystal NMR

Abstract

The two crystallographically distinct sites in Rb 2 CrO 4 are characterized in terms of their 87 Rb quadrupole coupling and chemical shielding anisotropy (CSA) interactions employing 87 Rb single-crystal NMR. Accurate values for the quadrupole coupling and CSA parameters are reported for both rubidium sites along with the direction cosines describing the orientation of the tensors for the NMR interactions with respect to the Rb 2 -CrO 4 crystal frame. The parameters for site 1 represent the first accurate investigation of this site, while the parameters for site 2 compare excellently with those previously reported. Some remarkable similarities are observed between the present parameters for Rb 2 CrO 4 and the 133 Cs parameters determined from recent magicangle spinning and single-crystal 133 Cs NMR studies for the isomorphous Cs 2 CrO 4 .

The Influence of the Radiofrequency Excitation and Conversion Pulses on the Lineshapes and Intensities of the Triple-Quantum MAS NMR Spectra of I=3/2 Nuclei

“…Experiments were performed on three samples: 23 Na in Na 2 SO 4 with a NQCC value of 2.6 MHz and an asymmetry parameter, η, of 0.6; and 87 Rb in Rb 2 CrO 4 , having two sites with NQCC values of 3.55 MHz (η = 0 36) and 9.4 MHz (η = 0 7) [35], and in Rb 2 SO 4 , with two sites that are temperature dependent. At a temperature of 48.2…”

Solid-State 87Rb NMR Study in Powdered RbMnCl3

“…At room temperature (∼290 K), the observed isotropic chemical shifts for two Rb sites in RbMnCl 3 , δ iso = 492 and 1005 ppm, are much larger than for other Rb sites; for examples, in Rb 2 CrO 4 with δ iso = −60(3) ppm and −8 7(2) ppm [12] and in RbClO 4 with δ iso = −13 7(6) ppm [13]. The very large chemical shift in RbMnCl 3 is related to the transferred hyperfine interaction [14] due to the paramagnetic property.…”

Improved Hardware and Software for Single-Crystal NMR Spectroscopy

“…spectra of the three rotational axes was only 5 h. The complete analysis of these spectra is given elsewhere (8).…”

“…Such cases include (i) complex powder spectra resulting from overlap of patterns from many different sites (4 -8), (ii) samples for which one of the interactions of interest is so weak that the effect of this interaction will be averaged by MAS even at low spinning frequencies (6,9) or is hidden in the line broadening of the dominating anisotropic interaction when observed from static spectra of powder samples (6, 7, 9 -12), and (iii) quadrupolar nuclei for which the quadrupole interaction is so strong that even the second-order broadening of the central transition is larger by more than an order of magnitude than the available spinning frequencies (7,8).…”