Uniaxial negative thermal expansion facilitated by weak host-guest interactions
Emile R Engel1, Vincent J Smith, Charl X Bezuidenhout
1Department of Chemistry and Polymer Science, University of Stellenbosch, Private Bag X1, Matieland, 7602, South Africa. ljb@sun.ac.za.
Chemical Communications (Cambridge, England)
|March 18, 2014
Summary
A nitromethane solvate of 18-crown-6 exhibits unusual thermal expansion, with significant contraction along one axis due to weak electrostatic interactions. This finding reveals the largest negative thermal expansion for an organic inclusion compound.
Area of Science:
- Crystal engineering
- Materials science
- Solid-state chemistry
Background:
- 18-crown-6 forms solvates with various molecules.
- Unusual unit cell behavior in solvates can lead to novel material properties.
- Thermal expansion is a critical parameter in material design.
Purpose of the Study:
- To investigate the thermal expansion of a nitromethane solvate of 18-crown-6.
- To understand the mechanism behind observed unit cell anomalies.
- To quantify the negative thermal expansion in this organic inclusion compound.
Main Methods:
- Variable-temperature single-crystal X-ray diffraction.
- Analysis of unit cell parameters under changing temperatures.
- Investigation of intermolecular interactions.
Main Results:
- Confirmed exceptionally large positive thermal expansion along two axial directions.
- Observed significant negative thermal expansion along the third axial direction.
- Quantified a linear thermal expansion coefficient of -129 × 10(-6) K(-1).
Conclusions:
- The nitromethane solvate of 18-crown-6 displays anisotropic thermal expansion.
- Weak electrostatic interactions are the primary drivers of this unique behavior.
- This compound exhibits the largest negative thermal expansion reported for an organic inclusion compound, offering potential for novel applications.
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