Chapter 5 Chlorine, Bromine, and Iodine Solid-State NMR Spectroscopy

Widdifield, Cory M.; Chapman, Rebecca P.; Bryce, David L.

doi:10.1016/s0066-4103(08)00405-5

Cited by 56 publications

(73 citation statements)

References 419 publications

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“…Thus, a comparison of theoretical and experimental magnetic shielding (maybe together with a comparison of computed electric field gradients and experimental quadrupole splittings 57 ) may provide an interesting and alternative test of DFT functionals as compared to more common total energy or band gap calculations. [43,44] * The cited shielding has been converted to absolute shifts using our value for KBr.…”

Section: Discussionmentioning

confidence: 99%

Assessment of DFT functionals with NMR chemical shifts

2013

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Density-functional theory (DFT) calculations of the magnetic shielding for nuclear magnetic resonance (NMR) in solids provide an important contribution for understanding the experimentally observed chemical shifts. It is known that the calculated NMR shielding parameters for a particular nucleus in a series of compounds correlate well with the experimentally measured chemical shifts; however, the slope of a linear fit often differs from the ideal value of 1.0. Focusing on a series of ionic compounds (fluorides, oxides, bromides, and chlorides), we show that the error is caused by the generalized gradient approximation (GGA) to the exchange-correlation functional and it is related to the well-known band-gap problem. In order to devise an ab initio approach that would correctly reproduce the variation of the shifts within a series of compounds, we test various DFT based approaches. A simple GGA + U scheme with the orbital field acting on the cation d states does not work in a general way. Also, the popular hybrid functionals (including the screened versions), which contain some fixed amount of exact exchange, lead to a large overestimation of the necessary slope correction. Surprisingly, the best solution to this problem is offered by a semilocal potential designed by Becke and Johnson to reproduce the optimized exact exchange potential in free atoms. Density functional theory (DFT) calculations of the magnetic shielding for nuclear magnetic resonance (NMR) in solids provide an important contribution for understanding the experimentally observed chemical shifts. It is known that the calculated NMR shielding parameters for a particular nucleus in a series of compounds correlate well with the experimentally measured chemical shifts, however, the slope of a linear fit often differs from the ideal value of 1.0. Focusing on a series of ionic compounds (fluorides, oxides, bromides and chlorides), we show that the error is caused by the generalized gradient approximation (GGA) to the exchange correlation functional and it is related to the well known band-gap problem. In order to devise an ab-initio approach that would correctly reproduce the variation of the shifts within a series of compounds, we test various DFT based approaches. A simple GGA+U scheme with the orbital field acting on the cation d-states does not work in a general way. Also the popular hybrid functionals (like HSE or YS-PBE0), which contain some fixed amount of exact exchange, leads to a large overestimation of the necessary slope correction. Surprisingly, the best solution to this problem is offered by a semi-local potential designed by Becke and Johnson to reproduce the optimized exact exchange potential in free atoms.

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Section: Discussionmentioning

confidence: 99%

Assessment of DFT functionals with NMR chemical shifts

2013

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“…Therefore, the quadrupolar and isotropic chemical shift (δiso) parameters were easily extracted from the spectrum observed at 24 T with a SIMPSON simulation: (χQ, η, δiso) = (4.26 MHz, 0.75, 110 ppm) despite these parameters hardly to obtain from that at 14.1 T. These parameters agree well with the previously reported values. 19,20 The distortions in the lineshape observed at 14.1 T are mainly due to the combined effect of the broad lineshape and the dead time in NMR measurements. The first few sampling points of the FID were found to be absent in the NMR experiments during the dead time due to some technical difficulty in observing the signal just after the rf pulses.…”

Section: Resultsmentioning

confidence: 99%

“…Since chloride is a quite important nucleus in pharmaceutical, organic, and inorganic chemistry, both 35 Cl and 37 Cl have been extensively studied. [19][20][21][22][23][24][25][26][27] To demonstrate the advantage of the high magnetic field, we propose a simple theoretical model a) to predict the sensitivity enhancement at higher magnetic fields, and b) to estimate the isotope effect. In the present study, this model is experimentally verified utilizing 35 Cl and 37 Cl solid-state NMR at two different magnetic fields.…”

Section: Introductionmentioning

confidence: 99%

24 T High-Resolution and -Sensitivity Solid-State NMR Measurements of Low-Gamma Half-Integer Quadrupolar Nuclei 35Cl and 37Cl

Pandey

Hashi²,

Ohki³

et al. 2016

ANAL. SCI.

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Solid-state NMR observations of low-gamma half-integer quadrupolar nuclei, 35 Cl and 37 Cl, were demonstrated using a 24 T hybrid magnet ( 1 H resonance frequency of 1.02 GHz) comprised of the high-temperature (HTS) and low-temperature (LTS) superconductors, and compared with results using a 14.1 T standard NMR magnet. While at 24 T the linewidth is 1.7 times narrower than that at 14.1 T, the gain in the sensitivity is 7.0 times because of enhanced polarization, reduced linewidth, and the use of larger rotor. A simple theoretical model was used to rationalize the sensitivity enhancements. The ratio of 35 Cl and 37 Cl quadrupolar couplings agrees well with the ratio of quadrupolar moments, and no isotopedependent chemical shift has been observed. In addition, the 3QMAS spectrum of 35 Cl is shown to demonstrate the high sensitivity rendered by the 24 T spectrometer.

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“…1) have spin quantum numbers greater than 1/2 and are called quadrupolar nuclei. Indeed, the stable isotopes of chlorine, bromine, and iodine are all quadrupolar [28][29][30]. The NMR spectra of such nuclei are influenced by the interaction between the quadrupole moment of the nucleus (Q) and the electric field gradient (EFG) at the nucleus.…”

Section: The Nuclear Electric Quadrupolar Interactionmentioning

confidence: 99%

“…This means that, for a given chemical environment (and fixed EFG), the quadrupolar coupling constant and NMR powder pattern breadth will be largest for 127 I and smallest for 37 Cl. In practice this means that 127 I NMR spectroscopy is extremely challenging and there are relatively few reports in the literature [30].…”

Section: The Nuclear Electric Quadrupolar Interactionmentioning

confidence: 99%

Solid-State NMR Study of Halogen-Bonded Adducts

Bryce

Viger‐Gravel

2014

Topics in Current Chemistry

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Nuclear magnetic resonance (NMR) spectroscopy offers unique insights into halogen bonds. NMR parameters such as chemical shifts, quadrupolar coupling constants, J coupling constants, and dipolar coupling constants are in principle sensitive to the formation and local structure of a halogen bond. Carrying out NMR experiments on halogen-bonded adducts in the solid state may provide several advantages over solution studies including (1) the absence of solvent which can interact with halogen bond donor sites and complicate spectral interpretation, (2) the lack of a need for single crystals or even long-range crystalline order, and (3) the potential to measure complete NMR interaction tensors rather than simply their isotropic values. In this chapter, we provide an overview of the NMR interactions and experiments which are relevant to the study of nuclei which are often found in halogen bonds (RX···Y) including (13)C, (35/37)Cl, (79/81)Br, (127)I, (77)Se, and (14/15)N. Experimental examples based on iodoperfluorobenzene halides, bis(trimethylammonium)alkane diiodide, and selenocyanate complexes, as well as haloanilinium halides, are discussed. Of particular interest is the sensitivity of the isotropic chemical shifts, the chemical shift tensor spans, and the halide nuclear electric quadrupolar coupling tensors to the halogen bond geometry in such compounds. Technical limitations associated with the NMR spectroscopy of covalently-bonded halogens are underlined.

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Chapter 5 Chlorine, Bromine, and Iodine Solid-State NMR Spectroscopy

Cited by 56 publications

References 419 publications

Assessment of DFT functionals with NMR chemical shifts

Assessment of DFT functionals with NMR chemical shifts

24 T High-Resolution and -Sensitivity Solid-State NMR Measurements of Low-Gamma Half-Integer Quadrupolar Nuclei 35Cl and 37Cl

Solid-State NMR Study of Halogen-Bonded Adducts

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