HIGH-FIELD SOLID-STATE <sup>35</sup>Cl NMR IN SELENIUM(IV) AND TELLURIUM(IV) HEXACHLORIDES
We report solid-state <sup>35</sup>Cl NMR spectra in three hexachlorides, (NH<sub>4</sub>)<sub>2</sub>SeCl<sub>6</sub>, (NH<sub>4</sub>)<sub>2</sub>TeCl<sub>6</sub> and Rb<sub>2</sub>TeCl<sub>6</sub>. The C<sub>Q</sub> (<sup>35</sup>Cl) quadrupole coupling constants in the three compounds were found to be 41.4±0.1 MHz, 30.3±0.1 MHz and 30.3±0.1 MHz, respectively, some of the largest C<sub>Q</sub> (<sup>35</sup>Cl) quadrupole coupling constants ever measured in polycrystalline powdered solids directly via <sup>35</sup>Cl NMR spectroscopy. The <sup>35</sup>Cl EFG tensors are axial in all three cases reflecting the C <sub>4 v </sub> point group symmetry of the chlorine sites. <sup>35</sup>Cl NMR experiments in these compounds were only made possible by employing the WURST-QCPMG pulse sequence in the ultrahigh magnetic field of 21.1 T. <sup>35</sup>Cl NMR results agree with the earlier reported <sup>35</sup>Cl NQR values and with the complementary plane-wave DFT calculations. The origin of the very large C<sub>Q</sub> (<sup>35</sup>Cl) quadrupole coupling constants in these and other main-group chlorides lies in the covalent-type chlorine bonding. The ionic bonding in the ionic chlorides results in significantly reduced C<sub>Q</sub> (<sup>35</sup>Cl) values as illustrated with triphenyltellurium chloride Ph<sub>3</sub>TeCl. The high sensitivity of <sup>35</sup>Cl NMR to the chlorine coordination environment is demonstrated using tetrachlorohydroxotellurate hydrate K[TeCl<sub>4</sub>(OH)]×0.5H<sub>2</sub>O as an example. <sup>125</sup>Te MAS NMR experiments were performed for tellurium compounds to support <sup>35</sup>Cl NMR findings.