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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.


Related in: MedlinePlus

The effects of a 5% reduction in the a and c axis lengths on intermolecular contact energies. The energies were calculated for different model structures using the PIXEL method. Model ‘opt’ refers to the structure at 0.22 GPa after optimisation of the coordinates using DFT (holding the cell dimensions fixed). Model ‘A’ was obtained from model ‘opt’ by reducing the length of the a-axis by 5% and re-optimising the structure. Model ‘C’ was obtained in a similar way, but after reducing the length of the c-axis by 5%. The Figures 3 and 5etc. on the right of the figure refer to the contact numbers listed on the far left of Table 2. Contacts 4, 6, 10 and 12 are symmetry equivalent to those shown. The H-bond contacts 1 and 2 are omitted for clarity.
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Fig11: The effects of a 5% reduction in the a and c axis lengths on intermolecular contact energies. The energies were calculated for different model structures using the PIXEL method. Model ‘opt’ refers to the structure at 0.22 GPa after optimisation of the coordinates using DFT (holding the cell dimensions fixed). Model ‘A’ was obtained from model ‘opt’ by reducing the length of the a-axis by 5% and re-optimising the structure. Model ‘C’ was obtained in a similar way, but after reducing the length of the c-axis by 5%. The Figures 3 and 5etc. on the right of the figure refer to the contact numbers listed on the far left of Table 2. Contacts 4, 6, 10 and 12 are symmetry equivalent to those shown. The H-bond contacts 1 and 2 are omitted for clarity.

Mentions: The energies of other contacts are depicted in Figure 11. In all but one case (#5), the contacts in structure C are less energetic that those in A, indicating that compression along c destabilises the inter-chain van der Waals interactions more than compression along a. While this explains the greater compressibility along the a-direction, it is also clear that the balance is a rather fine one, and this is manifested in the variable pressure series by the more isotropic strain tensor. As pressure increases, the PV contribution to free energy becomes appreciable. As Figure 10 shows, closure of the interstitial voids involves a significant component of c-axis shortening, and the isotropy of strain at high pressure is the result of compression along a being favoured by the inter-chain contacts, while compression along c leads to greater volume reduction.Figure 11


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

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

The effects of a 5% reduction in the a and c axis lengths on intermolecular contact energies. The energies were calculated for different model structures using the PIXEL method. Model ‘opt’ refers to the structure at 0.22 GPa after optimisation of the coordinates using DFT (holding the cell dimensions fixed). Model ‘A’ was obtained from model ‘opt’ by reducing the length of the a-axis by 5% and re-optimising the structure. Model ‘C’ was obtained in a similar way, but after reducing the length of the c-axis by 5%. The Figures 3 and 5etc. on the right of the figure refer to the contact numbers listed on the far left of Table 2. Contacts 4, 6, 10 and 12 are symmetry equivalent to those shown. The H-bond contacts 1 and 2 are omitted for clarity.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig11: The effects of a 5% reduction in the a and c axis lengths on intermolecular contact energies. The energies were calculated for different model structures using the PIXEL method. Model ‘opt’ refers to the structure at 0.22 GPa after optimisation of the coordinates using DFT (holding the cell dimensions fixed). Model ‘A’ was obtained from model ‘opt’ by reducing the length of the a-axis by 5% and re-optimising the structure. Model ‘C’ was obtained in a similar way, but after reducing the length of the c-axis by 5%. The Figures 3 and 5etc. on the right of the figure refer to the contact numbers listed on the far left of Table 2. Contacts 4, 6, 10 and 12 are symmetry equivalent to those shown. The H-bond contacts 1 and 2 are omitted for clarity.
Mentions: The energies of other contacts are depicted in Figure 11. In all but one case (#5), the contacts in structure C are less energetic that those in A, indicating that compression along c destabilises the inter-chain van der Waals interactions more than compression along a. While this explains the greater compressibility along the a-direction, it is also clear that the balance is a rather fine one, and this is manifested in the variable pressure series by the more isotropic strain tensor. As pressure increases, the PV contribution to free energy becomes appreciable. As Figure 10 shows, closure of the interstitial voids involves a significant component of c-axis shortening, and the isotropy of strain at high pressure is the result of compression along a being favoured by the inter-chain contacts, while compression along c leads to greater volume reduction.Figure 11

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