A novel 1:1 benzenesulfonamide: 18-crown-6 complex as uncovered via 13C solid phase NMR spectroscopy and X-ray crystallography

A 1:1 complex of 18-crown-6 ether and benzenesulfonamide has been prepared, whose melting point is within 4° of the previously reported 1:2 complex. The X-ray crystallographic structure shows pseudo D3d symmetry in the crown ether portion of this complex, in contrast to the 1:2 complex, which exhibits Ci symmetry in the macrocycle. The temperature dependent 13C CPMAS NMR spectra of these complexes have two regions of broadening for the crown ether carbons. At higher temperatures, a dipolar "washout" mechanism is operative, leading to broadening when molecular motion has a correlation time approximately equal to the inverse of the decoupling field. At lower temperatures broadening occurs when the motional correlation time is equal to the inverse of the chemical shift difference. From application of the Arrhenius equation, the activation energy for the molecular motion in solid 18-crown-6 is found to be approximately 10kcal/mol. Evidence for independent anisotropic motion in the benzenesulfonamide moiety of the 1:1 complex is also presented. Keywords: crown ether, molecular motion, solid phase NMR.

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The 18-crown-6.2 chloroacetonitrile complex. X-ray crystal structure and solid phase motions of guest and host as studied by variable temperature 13C CPMAS NMR spectroscopy

Canadian Journal of Chemistry ◽

10.1139/v92-138 ◽

1992 ◽

Vol 70 (4) ◽

pp. 1033-1041 ◽

Cited By ~ 5

Author(s):

G. W. Buchanan ◽

A. Rodrigue ◽

C. Bensimon ◽

C. I. Ratcliffe

Keyword(s):

Activation Energy ◽

Correlation Time ◽

Molecular Motion ◽

Solid Phase ◽

Variable Temperature ◽

13C Cpmas Nmr ◽

X Ray ◽

Guest Species ◽

Motional Correlation Time ◽

13C Cpmas Nmr Spectroscopy

The title complex has two distinct 18-crown-6 moieties of approximate D3d symmetry in the unit cell. The 45.3 MHz 13C CPMAS spectra have two regions of broadening for the crown ether carbons. At high temperatures a dipolar washout mechanism is operative, leading to broadening when molecular motion has a correlation time approximately equal to the inverse of the decoupling field. At lower temperatures broadening occurs when the motional correlation time is equal to the inverse of the chemical shift difference. The activation energy for 18-crown-6 reorientation in this solid is calculated to be ca. 48 kJ/mol. For the chloroacetonitrile, the CH2 carbon also shows dipolar washout, but at a temperature much lower than the 18-crown-6. The activation energy for reorientation for this "guest species" is ca. 42 kJ/mol.

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Howard Flack and the Flack Parameter

Chemistry ◽

10.3390/chemistry2040052 ◽

2020 ◽

Vol 2 (4) ◽

pp. 796-804

Author(s):

David John Watkin ◽

Richard Ian Cooper

Keyword(s):

Structure Determination ◽

Standard Uncertainty ◽

Crystallographic Structure ◽

X Ray ◽

Original Algorithm ◽

X Ray Crystallography ◽

Chiral Materials

The Flack Parameter is now almost universally reported for all chiral materials characterized by X-ray crystallography. Its elegant simplicity was an inspired development by Howard Flack, and although the original algorithm for its computation has been strengthened by other workers, it remains an essential outcome for any crystallographic structure determination. As with any one-parameter metric, it needs to be interpreted in the context of its standard uncertainty.

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Molecular cleft or tweezer compounds derived from trioxabicyclo[3.3.1]nonadiene diisocyanate and diacid dichloride

Beilstein Journal of Organic Chemistry ◽

10.3762/bjoc.11.1 ◽

2015 ◽

Vol 11 ◽

pp. 1-8 ◽

Cited By ~ 3

Author(s):

Gert Kollenz ◽

Ralf Smounig ◽

Ferdinand Belaj ◽

David Kvaskoff ◽

Curt Wentrup

Keyword(s):

Rare Earth ◽

Crown Ether ◽

Dft Calculations ◽

Metal Ions ◽

Rare Earth Metal ◽

Alkaline Earth ◽

Earth Metal ◽

X Ray ◽

X Ray Crystallography ◽

Derivatives Of

The structures of two derivatives of the bisdioxine diisocyanate 1, the bisurea 4 and the biscarbamate 5, are established by X-ray crystallography and DFT calculations. These compounds possess endo,endo structures, in the case of the bisurea 4 with two nearly parallel pendant chains. The X-ray structures are reproduced very well by DFT calculations. Similar endo,endo conformations are calculated for the bisamide crown ether derivatives 7, where two proximate and nearly parallel crown ether units endow the molecules with a claw-like molecular cleft or tweezer structure as evidenced by an enhanced ability to extract some alkali, alkaline earth and rare earth metal ions.

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The Stereo Structures of Some Mycophenolic Acid Derivatives

Australian Journal of Chemistry ◽

10.1071/ch06481 ◽

2007 ◽

Vol 60 (5) ◽

pp. 354 ◽

Cited By ~ 1

Author(s):

Paul V. Bernhardt ◽

Raymond M. Carman ◽

Tri T. Le

Keyword(s):

Mycophenolic Acid ◽

Crystallographic Structure ◽

X Ray ◽

X Ray Crystallography

X-Ray crystallography affords the stereochemistry of three iodo compounds derived from mycophenolic acid. These included the crystallographic structure of a tertiary iodide.

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Charting Hydrogen Bond Anisotropy

10.26434/chemrxiv.8865944 ◽

2019 ◽

Author(s):

Diogo Santos-Martins ◽

Stefano Forli

Keyword(s):

Hydrogen Bond ◽

Chemical Biology ◽

Solid Phase ◽

Electronic Configuration ◽

Interaction Energies ◽

X Ray ◽

X Ray Crystallography ◽

Chemical Groups ◽

High Degree ◽

Context Free

<div>Hydrogen bond (HB) is an essential interaction in countless phenomena, and regulates the chemistry of life. HBs are characterized by two main features, strength and directionality, with a high degree of heterogeneity across different chemical groups. These characteristics are dependent on the electronic configuration of the atoms involved in the interaction, which, in turn, is influenced strongly by the molecular environment where they are found. Studies based on the analysis of HB in solid phase, such as X-ray crystallography, suffer from significant biases due to the packing forces. These will tend to better describe strong HBs at the expenses of weak ones, which are either distorted or under represented. Using quantum mechanics (QM), we calculated interaction energies for about a hundred acceptor and donors, in a rigorously defined set of geometries. We performed about 180,000 independent QM calculations, covering all relevant angular components, and mapping strength and directionality in a context free from external biases, with both single-site and cooperative HBs. We show that by quantifying directionality, there is not correlation with strength, and therefore these two components need to be addressed separately. Results demonstrate that there are very strong HB acceptors (e.g.,DMSO) with nearly isotropic interactions, and weak ones (e.g.,thioacetone) with a sharp directional profile. Similarly, groups can have comparable directional propensity, but be very distant in the strength spectrum (e.g., thioacetone and pyridine). These findings have implications for biophysics and molecular recognition, providing new insight for chemical biology, protein engineering, and drug design. The results require rethinking the way directionality is described, with implications for the thermodynamics of HB.</div>

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Improved Electronic Transport in Ion Complexes of Crown Ether Based Columnar Liquid Crystals

Crystals ◽

10.3390/cryst9020074 ◽

2019 ◽

Vol 9 (2) ◽

pp. 74 ◽

Cited By ~ 3

Author(s):

Peter Staffeld ◽

Martin Kaller ◽

Philipp Ehni ◽

Max Ebert ◽

Sabine Laschat ◽

...

Keyword(s):

Ionic Conductivity ◽

Crown Ether ◽

Electronic Transport ◽

Columnar Structure ◽

Strong Increase ◽

Temperature Dependent ◽

X Ray ◽

X Ray Scattering ◽

Structural And Electronic Properties ◽

The Stability

The Li+- and K+-complexes of new discotic mesogens, where two n-alkoxy-substituted triphenylene cores are connected by a central crown ether (12-crown-4 and 18-crown-6), provide interesting structural and electronic properties. The inter- and intra-columnar structure was investigated by small and wide angle X-ray scattering. The electronic and ionic transports were studied by temperature dependent photoconductivity and impedance spectroscopy, respectively. Besides a strong increase of the stability and the width of the columnar phases the presence of soft anions (iodide, thiocyanate, tetrafluoroborate) leads to an improved intra-columnar order. The hereby shortened stacking-distance of the triphenylene cores leads to a significant increase of the photoconductivity in the columnar mesophase. Furthermore, the ionic conductivity of the new materials was investigated on macroscopically aligned thin films. The existence of channels for fast cation transport formed by the stacked crown ether moieties in the centre of each column can be excluded. The cations are coordinated strongly and therefore contributing only little to the conductivity. The ionic conductivity is dominated by the anisotropic migration of the non-coordinated anions through the liquid, like side chains favouring the propagation parallel to the columns. Iodide migrates about 20 times faster than thiocyanate and 100 times faster than tetrafluoroborate.

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The X-Ray Crystallographic Structure of a 1,2-Dibromo-4,8-epoxy-p-menthane

Australian Journal of Chemistry ◽

10.1071/ch9960925 ◽

1996 ◽

Vol 49 (8) ◽

pp. 925 ◽

Cited By ~ 1

Author(s):

RM Carman ◽

RA Edwards ◽

AC Rayner ◽

WT Robinson

Keyword(s):

Crystallographic Structure ◽

X Ray ◽

X Ray Crystallography

The crystalline dibromo epoxide obtained from (R)-α- terpineol is shown by X-ray crystallography to have the (1S,2S,4S)-1,2-dibromo-4,8-epoxy-p-menthane structure (3).

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