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The effect of temperature and pressure on the crystal structure of piperidine.

Budd LE, Ibberson RM, Marshall WG, Parsons S - Chem Cent J (2015)

Bottom Line: Analysis of the thermal expansion data in the light of phonon frequencies determined in periodic DFT calculations indicates that the expansion at very low temperature is governed by external lattice modes, but above 100 K the influence of intramolecular ring-flexing modes also becomes significant.The principal directions of thermal expansion are determined by the sensitivity of different van der Waals interactions to changes in distance.The principal values of the strain developed on application of pressure are similarly oriented to those determined in the variable-temperature study, but more isotropic because of the need to minimise volume by filling interstitial voids at elevated pressure.

View Article: PubMed Central - PubMed

Affiliation: EaStCHEM School of Chemistry and Centre for Science at Extreme Conditions, The University of Edinburgh, King's Buildings, West Mains Road, Edinburgh, EH9 3FJ UK.

ABSTRACT

Background: The response of molecular crystal structures to changes in externally applied conditions such as temperature and pressure are the result of a complex balance between strong intramolecular bonding, medium strength intermolecular interactions such as hydrogen bonds, and weaker intermolecular van der Waals contacts. At high pressure the additional thermodynamic requirement to fill space efficiently becomes increasingly important.

Results: The crystal structure of piperidine-d11 has been determined at 2 K and at room temperature at pressures between 0.22 and 1.09 GPa. Unit cell dimensions have been determined between 2 and 255 K, and at pressures up to 2.77 GPa at room temperature. All measurements were made using neutron powder diffraction. The crystal structure features chains of molecules formed by NH…N H-bonds with van der Waals interactions between the chains. Although the H-bonds are the strongest intermolecular contacts, the majority of the sublimation enthalpy may be ascribed to weaker but more numerous van der Waals interactions.

Conclusions: Analysis of the thermal expansion data in the light of phonon frequencies determined in periodic DFT calculations indicates that the expansion at very low temperature is governed by external lattice modes, but above 100 K the influence of intramolecular ring-flexing modes also becomes significant. The principal directions of thermal expansion are determined by the sensitivity of different van der Waals interactions to changes in distance. The principal values of the strain developed on application of pressure are similarly oriented to those determined in the variable-temperature study, but more isotropic because of the need to minimise volume by filling interstitial voids at elevated pressure. Graphical AbstractThough H-bonds are important interactions in the crystal structure of piperidine, the response to externally-applied conditions are determined by van der Waals interactions.

No MeSH data available.


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Largest eigenvalues of the rigid body thermal motion libration tensor L, determined (a) from experimental data at 2 K and (b) from a periodic DFT phonon calculation.
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Fig4: Largest eigenvalues of the rigid body thermal motion libration tensor L, determined (a) from experimental data at 2 K and (b) from a periodic DFT phonon calculation.

Mentions: Anisotropic displacement parameters were modelled using TLS rigid-body constraints [23,24]. The two largest principal axes of the libration tensor, shown in Figure 4a are located in the mean plane of the molecule with magnitudes of approximately 19 degrees2, with the third, out-of-plane, axis having a magnitude of 4.2 degrees2. These data indicate that at 2 K the molecular motion consists mainly of in-plane rocking vibrations. This description of the molecular motion is broadly reproduced in the displacement parameters calculated from the periodic DFT phonon calculations (Figure 4b). The two in-plane L tensor eigenvalues have magnitudes of 12.0 and 15.0 degrees2, with the third axis having a value of 5.8 degrees2. The corresponding in-plane eigenvectors, though similar, are rotated by 29.6° relative to the experimental values. Considering the approximations made in the calculations (e.g. harmonicity), the nearly isotropic cross-section of the L tensor, the tendency for displacement parameters to ‘mop-up’ experimental errors such as absorption and the fact that the atomic motions are independent and not part of a rigid body in the DFT calculation, the overall the agreement between the experimental and theoretical results is quite satisfactory.Figure 4


The effect of temperature and pressure on the crystal structure of piperidine.

Budd LE, Ibberson RM, Marshall WG, Parsons S - Chem Cent J (2015)

Largest eigenvalues of the rigid body thermal motion libration tensor L, determined (a) from experimental data at 2 K and (b) from a periodic DFT phonon calculation.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4403828&req=5

Fig4: Largest eigenvalues of the rigid body thermal motion libration tensor L, determined (a) from experimental data at 2 K and (b) from a periodic DFT phonon calculation.
Mentions: Anisotropic displacement parameters were modelled using TLS rigid-body constraints [23,24]. The two largest principal axes of the libration tensor, shown in Figure 4a are located in the mean plane of the molecule with magnitudes of approximately 19 degrees2, with the third, out-of-plane, axis having a magnitude of 4.2 degrees2. These data indicate that at 2 K the molecular motion consists mainly of in-plane rocking vibrations. This description of the molecular motion is broadly reproduced in the displacement parameters calculated from the periodic DFT phonon calculations (Figure 4b). The two in-plane L tensor eigenvalues have magnitudes of 12.0 and 15.0 degrees2, with the third axis having a value of 5.8 degrees2. The corresponding in-plane eigenvectors, though similar, are rotated by 29.6° relative to the experimental values. Considering the approximations made in the calculations (e.g. harmonicity), the nearly isotropic cross-section of the L tensor, the tendency for displacement parameters to ‘mop-up’ experimental errors such as absorption and the fact that the atomic motions are independent and not part of a rigid body in the DFT calculation, the overall the agreement between the experimental and theoretical results is quite satisfactory.Figure 4

Bottom Line: Analysis of the thermal expansion data in the light of phonon frequencies determined in periodic DFT calculations indicates that the expansion at very low temperature is governed by external lattice modes, but above 100 K the influence of intramolecular ring-flexing modes also becomes significant.The principal directions of thermal expansion are determined by the sensitivity of different van der Waals interactions to changes in distance.The principal values of the strain developed on application of pressure are similarly oriented to those determined in the variable-temperature study, but more isotropic because of the need to minimise volume by filling interstitial voids at elevated pressure.

View Article: PubMed Central - PubMed

Affiliation: EaStCHEM School of Chemistry and Centre for Science at Extreme Conditions, The University of Edinburgh, King's Buildings, West Mains Road, Edinburgh, EH9 3FJ UK.

ABSTRACT

Background: The response of molecular crystal structures to changes in externally applied conditions such as temperature and pressure are the result of a complex balance between strong intramolecular bonding, medium strength intermolecular interactions such as hydrogen bonds, and weaker intermolecular van der Waals contacts. At high pressure the additional thermodynamic requirement to fill space efficiently becomes increasingly important.

Results: The crystal structure of piperidine-d11 has been determined at 2 K and at room temperature at pressures between 0.22 and 1.09 GPa. Unit cell dimensions have been determined between 2 and 255 K, and at pressures up to 2.77 GPa at room temperature. All measurements were made using neutron powder diffraction. The crystal structure features chains of molecules formed by NH…N H-bonds with van der Waals interactions between the chains. Although the H-bonds are the strongest intermolecular contacts, the majority of the sublimation enthalpy may be ascribed to weaker but more numerous van der Waals interactions.

Conclusions: Analysis of the thermal expansion data in the light of phonon frequencies determined in periodic DFT calculations indicates that the expansion at very low temperature is governed by external lattice modes, but above 100 K the influence of intramolecular ring-flexing modes also becomes significant. The principal directions of thermal expansion are determined by the sensitivity of different van der Waals interactions to changes in distance. The principal values of the strain developed on application of pressure are similarly oriented to those determined in the variable-temperature study, but more isotropic because of the need to minimise volume by filling interstitial voids at elevated pressure. Graphical AbstractThough H-bonds are important interactions in the crystal structure of piperidine, the response to externally-applied conditions are determined by van der Waals interactions.

No MeSH data available.


Related in: MedlinePlus