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Conformational polymorphs of 1,1,2,2-tetrachloroethane: pressure vs. temperature
Maciej Bujak1, Dieter Bläser, Andrzej Katrusiak
1Faculty of Chemistry, University of Opole, Oleska 48, 45-052 Opole, Poland. mbujak@uni.opole.pl
Chemical Communications (Cambridge, England)
|May 28, 2011
Summary
Chlorine-chlorine interactions dictate how 1,1,2,2-tetrachloroethane molecules pack in crystals. Low-density structures form via specific chlorine contacts and synclinal conformations, while high-pressure packing uses antiperiplanar forms.
Area of Science:
- Solid-state chemistry
- Crystallography
- Molecular interactions
Background:
- Understanding molecular aggregation is crucial for predicting material properties.
- The crystalline state of halogenated ethanes presents complex packing arrangements.
- Chlorine-chlorine (Cl···Cl) interactions play a significant role in molecular assembly.
Purpose of the Study:
- To elucidate the role of directional Cl···Cl interactions in the aggregation of 1,1,2,2-tetrachloroethane.
- To investigate the conformational preferences of 1,1,2,2-tetrachloroethane in different crystalline states.
- To determine the mechanism driving the transformation between low-density and high-density molecular packing.
Main Methods:
- Single-crystal X-ray diffraction at varying temperatures and pressures.
- Computational modeling to analyze intermolecular forces and conformational energies.
- Analysis of Cl···Cl contact types (Type I and Type II) and their geometric parameters.
Main Results:
- Low-density aggregation at low temperatures is governed by specific synclinal conformers and favored Cl···Cl contacts.
- High-pressure conditions promote dense packing through antiperiplanar conformers and less favored Cl···Cl contacts.
- The transition between packing densities involves the collapse of Cl···Cl contacts and conformational changes.
Conclusions:
- Directional Cl···Cl interactions are key determinants of 1,1,2,2-tetrachloroethane crystal structures.
- Conformational flexibility and electrostatic preferences dictate molecular packing under varying conditions.
- A mechanism involving contact collapse and conformational conversion explains the observed structural transitions.
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