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Combined Approach for the Structural Characterization of Alkali Fluoroscandates: Solid-State NMR, Powder X‑ray Diffraction, and Density Functional Theory Calculations
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 K<sub>5</sub>Sc<sub>3</sub>F<sub>14</sub> was fully determined from Rietveld refinement performed
on powder X-ray diffraction data. Moreover, the local structures of
NaScF<sub>4</sub>, Li<sub>3</sub>ScF<sub>6</sub>, KSc<sub>2</sub>F<sub>7</sub>, and Na<sub>3</sub>ScF<sub>6</sub> compounds were studied
in detail from solid-state <sup>19</sup>F and <sup>45</sup>Sc NMR
experiments. The <sup>45</sup>Sc chemical shift ranges for six- and
seven-coordinated scandium environments were defined. The <sup>19</sup>F chemical shift ranges for bridging and terminal fluorine atoms
were also determined. First-principles calculations of the <sup>19</sup>F and <sup>45</sup>Sc NMR parameters were carried out using plane-wave
basis sets and periodic boundary conditions (<i>CASTEP</i>), 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 <sup>45</sup>Sc NMR spectroscopy