HIGH-FIELD SOLID-STATE 35Cl NMR IN SELENIUM(IV) AND TELLURIUM(IV) HEXACHLORIDES
We report solid-state 35Cl NMR spectra in three hexachlorides, (NH4)2SeCl6, (NH4)2TeCl6 and Rb2TeCl6. The CQ(35Cl) quadrupole coupling constants in the three compounds were found to be 41.4r0.1 MHz, 30.3r0.1 MHz and 30.3r0.1 MHz, respectively, some of the largest CQ(35Cl) quadrupole coupling constants ever measured in polycrystalline powdered solids directly via 35Cl NMR spectroscopy. The 35Cl EFG tensors are axial in all three cases reflecting the C4v point group symmetry of the chlorine sites. 35Cl 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. 35Cl NMR results agree with the earlier reported 35Cl NQR values and with the complementary plane-wave DFT calculations. The origin of the very large CQ(35Cl) 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 CQ3(535Cl) values as illustrated with triphenyltellurium chloride Ph3TeCl. The high sensitivity of Cl NMR to the chlorine coordination environment is demonstrated using tetrachlorohydroxotellurate hydrate K[TeCl4(OH)]?0.5H2O as an35example. 125Te MAS NMR experiments were performed for tellurium compounds to support Cl NMR findings.
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The CQ(35Cl) quadrupole coupling constants in the three compounds were found to
be 41.40.1 MHz, 30.30.1 MHz and 30.30.1 MHz, respectively, some of the largest
CQ(35Cl) quadrupole coupling constants ever measured in polycrystalline powdered solids directly
via 35Cl NMR spectroscopy. <...> The 35Cl EFG tensors are axial in all three cases reflecting
the C4v point group symmetry of the chlorine sites. 35Cl 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. 35Cl NMR results agree with the earlier reported 35Cl NQR values
and with the complementary plane-wave DFT calculations. <...> The origin of the very large
CQ(35Cl) 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 CQ(35Cl) values as illustrated with triphenyltellurium chloride Ph3TeCl. <...> While the higher magnetic fields benefit NMR in general, it has been
found particularly advantageous for solid-state applications when dealing with quadrupolar nuclei. <...> In ionic and mostly organic salts, i.e. hydrochlorides in particular, CQ(35Cl) quadrupole
couplings are found in a convenient range of below 10 MHz, which allows for reasonably straightforward
recording of the spectral data and its subsequent analysis [16—19 ]. <...> In several transition
metal organometallic complexes containing chlorine ligands the 35Cl EFG tensor parameters measured
via 35Cl NMR were found to be sensitive to the chlorine bonding environment [21—23 ], which allowed
the differentiation between bridging, terminal-axial and terminal-equatorial chlorine sites. <...> The tour-de-force solid-state 35,37Cl NMR study of covalent organic chlorides,
the first study of its kind, was published very recently [ 26 ]. 35Cl and 37Cl NMR spectra recorded
for several solid organic chlorides with the use of the WURST-QCPMG pulse sequence were in excess
of 6—7 MHz broad, which is quite remarkable even at 21.1 T. Such strong 35,37Cl EFG interactions
necessitated the exact treatment of the Zeeman-quadrupolar (ZQ) interaction in modeling the
experimental spectra, since the second-order perturbation theory was no longer valid [ 27 ]. <...> In practice <...>
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