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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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Phonon density of states of piperidine-d11 calculated by periodic DFT.
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Fig6: Phonon density of states of piperidine-d11 calculated by periodic DFT.

Mentions: The Einstein temperatures extracted from the volume versus temperature data are in reasonable agreement with values determined from heat capacities (Cv) simulated as a function of temperature using the results of the DFT phonon calculations (121 and 801 K). The phonon density of states plot shown in Figure 6 suggests that the single-frequency model was unsuccessful because the low-frequency phonon region divides into one block at about 100 cm−1 composed of intermolecular modes, and a second from 200–500 cm−1 corresponding to intramolecular torsional modes such as ring-flexing. Both sets of vibrations contribute to the internal energy between 2 and 255 K, and both therefore need to be taken into account in the data-fitting model.Figure 6


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

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

Phonon density of states of piperidine-d11 calculated by periodic DFT.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig6: Phonon density of states of piperidine-d11 calculated by periodic DFT.
Mentions: The Einstein temperatures extracted from the volume versus temperature data are in reasonable agreement with values determined from heat capacities (Cv) simulated as a function of temperature using the results of the DFT phonon calculations (121 and 801 K). The phonon density of states plot shown in Figure 6 suggests that the single-frequency model was unsuccessful because the low-frequency phonon region divides into one block at about 100 cm−1 composed of intermolecular modes, and a second from 200–500 cm−1 corresponding to intramolecular torsional modes such as ring-flexing. Both sets of vibrations contribute to the internal energy between 2 and 255 K, and both therefore need to be taken into account in the data-fitting model.Figure 6

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