High-field solid-state 35Cl NMR in selenium(IV) and tellurium(IV) hexachlorides

We report solid-state Cl-35 NMR spectra in three hexachlorides, (NH4)(2)SeCl6, (NH4)(2)TeCl6 and Rb2TeCl6. The C (Q) (Cl-35) 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 (Q) (Cl-35) quadrupole coupling constants ever measured in polycrystalline powdered solids directly via Cl-35 NMR spectroscopy. The Cl-35 EFG tensors are axial in all three cases reflecting the C (4v) point group symmetry of the chlorine sites. Cl-35 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. Cl-35 NMR results agree with the earlier reported Cl-35 NQR values and with the complementary plane-wave DFT calculations. The origin of the very large C (Q) (Cl-35) 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 (Q) (Cl-35) values as illustrated with triphenyltellurium chloride Ph3TeCl. The high sensitivity of Cl-35 NMR to the chlorine coordination environment is demonstrated using tetrachlorohydroxotellurate hydrate K[TeCl4(OH)]a (TM) 0.5H(2)O as an example. Te-125 MAS NMR experiments were performed for tellurium compounds to support Cl-35 NMR findings.