Combined Approach for the Structural Characterization of Alkali Fluoroscandates: Solid-State NMR, Powder X-ray Diffraction, and Density Functional Theory Calculations

Abstract

The structures of several fluoroscandate compounds are presented here using a characterization approach combining powder X-ray diffraction and solid-state NMR. The structure of KScF was fully determined from Rietveld refinement performed on powder X-ray diffraction data. Moreover, the local structures of NaScF, LiScF, KScF, and NaScF compounds were studied in detail from solid-state F andSc NMR experiments. The Sc chemical shift ranges for six- and seven-coordinated scandium environments were defined. TheF chemical shift ranges for bridging and terminal fluorine atoms were also determined. First-principles calculations of the F andSc NMR parameters were carried out using plane-wave basis sets and periodic boundary conditions (CASTEP), and the results were compared with the experimental data. A good agreement between the calculated shielding constants and experimental chemical shifts was obtained. This demonstrates the good potential of computational methods in spectroscopic assignments of solid-state Sc NMR spectroscopy.

Combining solid state NMR, powder X-ray diffraction, and DFT calculations for CsSc3F10 structure determination

“…To convert the calculated isotropic chemical shielding into isotropic chemical shift, the definition of calibration curve relating isotropic chemical shift and shielding is necessary. For 45 Sc and 19 F the relationship reported in our previous study [6] are : δiso = -0.852×σiso+667.42 and δiso = -0.589×σiso +20.24, respectively.…”

“…We suppose that this is some unknown cesium fluoroscandates CsxScyFz. The chemical shift for the bridging fluorine atoms is ranging from -23 to -75 ppm [6], therefore, it can be concluded that each fluorine atom in the CsSc3F10 compound is bonded with two scandium atoms. respectively [6].…”

“…The Table 1). The very small peak of maximum at -33.9 ppm [6] and showing a Lorentzian-Gaussian line shape, and was assigned to the secondary phase ScF3. Additionally spectrum shows 3 very small peaks at -3.2 ppm, -12.5 ppm and -55 ppm.…”

“…The necessary improvement of these different crystalline materials for these specific applications requires precise knowledge of the local structure and an accurate description of their structure. There are many reports on lithium, potassium, and sodium fluoroscandates (for example: LiScF4 [5], KSc2F7 [2,3], NaScF4 [1,2], and others [6]), but relatively little is known about rubidium-and cesium-containing fluoride compounds. We suppose that the main reasons for this lack of investigations are related to the high cost of ScF3 and the high corrosiveness and hygroscopicity of Rb and Cs fluorides.…”

<p>Synthesis, Characterization, and Pharmacodynamics Study of Enrofloxacin Mesylate</p>

“…X-ray powder diffraction characterization showed that EM has a distinct diffraction peak, compared with enrofloxacin, EM has the characteristics of diffraction peak in 2θ were 7.93, 9.61, 11.89, 22.07, 22.95, 23.68, 24.36, 24.97, 35.29, 35.97, respectively, indicating that it is a crystal. 37 In addition, the numbers of diffraction peaks of EM were greatly different from enrofloxacin, and the energetic peak of EM is less than that of enrofloxacin, indicating that EM crystals may have small particle size, which facilitates their rapid dissolution. The angular positions, and relative intensity, as well as the shape of the diffraction peaks of EM, are greatly different from enrofloxacin, indicating that mesylate and enrofloxacin are not a simple physical mixture, but mesylate reacts with enrofloxacin to form a crystal different from enrofloxacin.…”