Characterization of the Binary Nitrides VN and ScN by Solid-State NMR Spectroscopy

NMR spectra of polycrystalline samples of the binary nitrides ScN and VN were acquired under magic-angle spinning. The observed nuclides Sc-45, V-51 and N-14 are all quadrupolar nuclei with a spin I>1/2 ${I\char62 1/2}$ . However, due to the high symmetry of their rock-salt type structures, the spectra of the nitrides do not exhibit effects of quadrupolar or other anisotropic interactions of significant magnitude. This allows a relatively straightforward evaluation of the acquired spectra, leading to isotropic chemical shift values (delta(iso)) of -213 ppm ((VN)-V-51), 378 ppm ((VN)-N-14), 290 ppm ((ScN)-Sc-45) and 442 ppm ((ScN)-N-14) against commonly used reference standards. In the wider context of N-14-NMR of binary nitrides, it is shown that the distance of nitrogen to the nearest neighbour cation can be correlated to the observed chemical shift

Characterisation of contact twinning for cerussite, PbCO3, by single-crystal NMR spectroscopy

<jats:title>Abstract</jats:title><jats:p>Cerussite, <jats:inline-formula><jats:alternatives><jats:tex-math>$$\\hbox {PbCO}_3$$</jats:tex-math><mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\"> <mml:msub> <mml:mtext>PbCO</mml:mtext> <mml:mn>3</mml:mn> </mml:msub> </mml:math></jats:alternatives></jats:inline-formula>, like all members of the aragonite group, shows a tendency to form twins, due to high pseudo-symmetry within the crystal structure. We here demonstrate that the twin law of a cerussite contact twin may be established using only <jats:inline-formula><jats:alternatives><jats:tex-math>$$^{207}$$</jats:tex-math><mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\"> <mml:msup> <mml:mrow /> <mml:mn>207</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula>Pb-NMR spectroscopy. This is achieved by a global fit of several sets of orientation-dependent spectra acquired from the twin specimen, allowing to determine the relative orientation of the twin domains. Also, the full <jats:inline-formula><jats:alternatives><jats:tex-math>$$^{207}$$</jats:tex-math><mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\"> <mml:msup> <mml:mrow /> <mml:mn>207</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula>Pb chemical shift tensor in cerussite at room temperature is determined from these data, with the eigenvalues being <jats:inline-formula><jats:alternatives><jats:tex-math>$$\\delta _{11} = (-2315\\pm 1)$$</jats:tex-math><mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\"> <mml:mrow> <mml:msub> <mml:mi>δ</mml:mi> <mml:mn>11</mml:mn> </mml:msub> <mml:mo>=</mml:mo> <mml:mrow> <mml:mo>(</mml:mo> <mml:mo>-</mml:mo> <mml:mn>2315</mml:mn> <mml:mo>±</mml:mo> <mml:mn>1</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> ppm, <jats:inline-formula><jats:alternatives><jats:tex-math>$$\\delta _{22} = (-2492 \\pm 3)$$</jats:tex-math><mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\"> <mml:mrow> <mml:msub> <mml:mi>δ</mml:mi> <mml:mn>22</mml:mn> </mml:msub> <mml:mo>=</mml:mo> <mml:mrow> <mml:mo>(</mml:mo> <mml:mo>-</mml:mo> <mml:mn>2492</mml:mn> <mml:mo>±</mml:mo> <mml:mn>3</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> ppm, and <jats:inline-formula><jats:alternatives><jats:tex-math>$$\\delta _{33} = (-3071 \\pm 3)$$</jats:tex-math><mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\"> <mml:mrow> <mml:msub> <mml:mi>δ</mml:mi> <mml:mn>33</mml:mn> </mml:msub> <mml:mo>=</mml:mo> <mml:mrow> <mml:mo>(</mml:mo> <mml:mo>-</mml:mo> <mml:mn>3071</mml:mn> <mml:mo>±</mml:mo> <mml:mn>3</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> ppm.</jats:p&gt

Local Electronic Structure in AlN Studied by Single-Crystal ²⁷Al and ¹⁴N NMR and DFT Calculations

Both the chemical shift and quadrupole coupling tensors for 14 N and 27 Al in the wurtzite structure of aluminum nitride have been determined to high precision by single-crystal NMR spectroscopy. A homoepitaxially grown AlN single crystal with known morphology was used, which allowed for optical alignment of the crystal on the goniometer axis. From the analysis of the rotation patterns of 14 N ( I=1 ) and 27 Al ( I=5/2 ), the quadrupolar coupling constants were determined to χ(14N)=(8.19±0.02) kHz, and χ(27Al)=(1.914±0.001) MHz. The chemical shift parameters obtained from the data fit were δiso=−(292.6±0.6) ppm and δΔ=−(1.9±1.1) ppm for 14 N, and (after correcting for the second-order quadrupolar shift) δiso=(113.6±0.3) ppm and δΔ=(12.7±0.6) ppm for 27 Al. DFT calculations of the NMR parameters for non-optimized crystal geometries of AlN generally did not match the experimental values, whereas optimized geometries came close for 27 Al with χ¯¯calc=(1.791±0.003) MHz, but not for 14 N with χ¯¯calc=−(19.5±3.3) kHz

Characterisation of different polymorphs of tris(8-hydroxyquinolinato)aluminium(III) using solid-state NMR and DFT calculations

<p>Abstract</p> <p>Background</p> <p>Organic light emitting devices (OLED) are becoming important and characterisation of them, in terms of structure, charge distribution, and intermolecular interactions, is important. Tris(8-hydroxyquinolinato)-aluminium(III), known as Alq₃, an organomettalic complex has become a reference material of great importance in OLED. It is important to elucidate the structural details of Alq₃in its various isomeric and solvated forms. Solid-state nuclear magnetic resonance (NMR) is a useful tool for this which can also complement the information obtained with X-ray diffraction studies.</p> <p>Results</p> <p>We report here ²⁷Al one-dimensional (1D) and two-dimensional (2D) multiple-quantum magic-angle spinning (MQMAS) NMR studies of the meridional (<it>α</it>-phase) and the facial (<it>δ</it>-phase) isomeric forms of Alq₃. Quadrupolar parameters are estimated from the 1D spectra under MAS and anisotropic slices of the 2D spectra and also calculated using DFT (density functional theory) quantum-chemical calculations. We have also studied solvated phase of Alq₃containing ethanol in its lattice. We show that both the XRD patterns and the quadrupolar parameters of the solvated phase are different from both the <it>α</it>-phase and the <it>δ</it>-phase, although the fluorescence emission shows no substantial difference between the <it>α</it>-phase and the solvated phase. Moreover, we have shown that after the removal of ethanol from the matrix the solvated Alq₃has similar XRD patterns and quadrupolar parameters to that of the <it>α</it>-phase.</p> <p>Conclusion</p> <p>The 2D MQMAS experiments have shown that all the different modifications of Alq₃have ²⁷Al in single unique crystallographic site. The quadrupolar parameters predicted using the DFT calculation under the isodensity polarisable continuum model resemble closely the experimentally obtained values. The solvated phase of Alq₃containing ethanol has structural difference from the <it>α</it>-phase of Alq₃(containing meridional isomer) from the solid-state NMR studies. Solid-state NMR can hence be used as an effective complementary tool to XRD for characterisation and structural elucidation.</p

Forty years of carabid beetle research in Europe - from taxonomy, biology, ecology and population studies to bioindication, habitat assessment and conservation

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