Comparison between structural analyses of plastic and brittle crystals

Amoureux, Jean‐Paul; Foulon, M.

doi:10.1107/s0108768187097465

Cited by 46 publications

(43 citation statements)

References 11 publications

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“…Pawley refinement, 38 which minimizes the weighted R-factor, R wp , describing the agreement between the experimental and the simulated patterns, helps to confirm the indexing result and the systematic absences for the space group assessment. In order to determine the structure of the two crystalline phases we have built up the molecule of 1F-ada using the parameters defining the adamantane molecule C 10 H 16 , 39 replacing one hydrogen atom in the molecule of adamantane by a fluorine one. The carbon atom C 1 and the fluorine atom F are placed on the diagonal of the cube and the carbon atom C 2 is placed on a cube axis.…”

Section: Resultsmentioning

confidence: 99%

Structure and reorientational dynamics of 1-F-adamantane

Hassine

Negrier

Romanini

et al. 2016

Phys. Chem. Chem. Phys.

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The polymorphism and the dynamics of a simple rigid molecule (1-fluoro-adamantane) have been studied by means of xray powder diffraction and broadband dielectric spectroscopy. At temperatures below the melting, the molecule forms an orientationally disordered phase I with cubic-centered structure (Phase I, Fm 3 m, Z=4). This phase possesses eight equilibrium positions for the fluorine atom, with equal occupancies factors of 1/8. A solid-solid phase transition to a lowtemperature tetragonal phase (Phase II, P 4 21c, Z=2) reduces the statistical disorder to only four possible equivalent sites for the fluorine atom, with fractional occupancies of 1/4. The dynamics has been rationalized under the constraints imposed by the space group of the crystal structure determined by powder X-ray diffraction. The dielectric spectroscopy study reveals that the statistical disorder in Phase II is dynamic in character and is associated with reorientational jumps along the two-and three-fold axes. In the dielectric loss spectra, the cooperative (α) relaxation exhibits a shoulder on the high-frequency side. This remarkable finding clearly reveals the existence of two intrinsic reorientational processes associated with the exchange of the F atom along the four sites. In addition to such "bimodal" relaxation, a secondary Johari-Goldstein relaxation is detected at lower temperatures.

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Section: Resultsmentioning

confidence: 99%

Structure and reorientational dynamics of 1-F-adamantane

Hassine

Negrier

Romanini

et al. 2016

Phys. Chem. Chem. Phys.

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“…In a related reasoning, the Cl atom at C(1) and the H atoms at C (3,5) are the geometric equivalents of geminal methylene C atoms in adamantane (3). The distance d(H 2 C ··· CH 2 ) = 249.5 pm [27] is shorter than Σr(vdW)[C, C] = 340 pm [8] by 27 %. The short contact is evidence of steric crowding rather than of an attractive interaction between the C atoms of the methylene groups.…”

Section: Discussionmentioning

confidence: 98%

The Sum of van der Waals Radii – A Pitfall in the Search for Bonding

Schiemenz

2007

Zeitschrift Für Naturforschung B

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The most widely used criterion for the evaluation of chemical bonding, especially of weak bonding, are interatomic distances shorter than the sum of the van der Waals radii, d(X···Y) < Σr(vdW)[X, Y]. The shortcomings of these radii are, however, so serious, that illicit conclusions are easily arrived at. It is proposed to discard the 'shorter than Σr(vdW)' criterion altogether and to rely on alternative criteria.

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“…There are different types of disorder 3,4 observed in crystalline systems associated with various structural degrees of freedom of molecules. Globular-shape molecules such as adamantane 5,6 and its substituted compounds 7,8 are known to show disorder associated with orientational degrees of freedom resulting in the well-known plastic crystalline phase. 8 In the case of crystals of 2-methyl-1,3-cyclohexane dione 9 the disorder is associated with the onset of large-amplitude vibrations of methylene groups.…”

Section: Introductionmentioning

confidence: 99%

Temperature-induced dynamical conformational disorder in 4-vinyl benzoic acid molecular crystals: A molecular simulation study

Murugan

2005

The Journal of Chemical Physics

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Extensive molecular simulations are carried out as a function of temperature to understand and quantify the conformational disorder in molecular crystals of 4-vinyl benzoic acid. The conformational disorder is found to be dynamic and associated with a flip-flop motion of vinyl groups. The population of minor conformer is less than 3% up to 300 K and is 13.2% at 350 K and these results are consistent with the experimental observations. At still higher temperatures, the population of minor conformer increases up to 25%. The evolution of structure at both molecular and unit-cell level of the molecular crystal as a function of temperature has been characterized by various quantities such as radial distribution functions, average cell parameters, volume, and interaction energies. The van't Hoff plot shows a nonlinear behavior at lower temperatures as it has been reported recently by Ogawa and co-workers in the case of stilbene, azobenzene, and N-(4-methylbenzylidene)-4-methylaniline molecular crystals. A set of rigid body simulations were also carried out to quantify the effect of conformational disorder on structural quantities such as unit-cell volume and interaction energy. The anomalous shrinkage of vinyl C=C bond length as a function of temperature has been explained by combining the results of simulations and a set of constrained optimizations using ab initio electronic structure calculations for various molecular structures differing in torsional angle.

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Comparison between structural analyses of plastic and brittle crystals

Cited by 46 publications

References 11 publications

Structure and reorientational dynamics of 1-F-adamantane

Structure and reorientational dynamics of 1-F-adamantane

The Sum of van der Waals Radii – A Pitfall in the Search for Bonding

Temperature-induced dynamical conformational disorder in 4-vinyl benzoic acid molecular crystals: A molecular simulation study

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