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Commensurate and incommensurate hydrogen bonds. An exercise in crystal engineering
T L Nguyen1, F W Fowler, J W Lauher
1Department of Chemistry, State University of New York, Stony Brook, NY 11794, USA.
Journal of the American Chemical Society
|November 1, 2001
Summary
Ureas and oxamides typically form distinct hydrogen-bonded networks. Cocrystallization revealed that these molecules can form novel 2D beta-networks or unusual conformations, altering their typical structures.
Area of Science:
- Crystal Engineering
- Supramolecular Chemistry
- Materials Science
Background:
- Ureas and oxamides commonly form 1D alpha-networks via hydrogen bonding.
- These networks exhibit characteristic repeat distances: approximately 4.60 Å for ureas and 5.05 Å for oxamides.
Purpose of the Study:
- Investigate the cocrystallization behavior of glycine urea and glycine oxamide with bipyridine derivatives.
- Determine the structural outcomes when molecules with incommensurate network distances are forced to coexist in the same crystal.
Main Methods:
- Cocrystallization of urea and oxamide derivatives with bipyridine compounds.
- X-ray diffraction analysis of the resulting eight cocrystals.
Main Results:
- All-urea and all-oxamide cocrystals maintained their characteristic alpha-networks.
- Three mixed cocrystals formed 2D beta-networks with alternating urea and oxamide subnetworks, averaging 4.87 Å.
- One mixed crystal showed a normal urea alpha-network, while the oxamide adopted an intramolecularly hydrogen-bonded conformation.
Conclusions:
- Cocrystallization can lead to the formation of novel 2D beta-networks with averaged repeat distances.
- In some cases, competing network formation can induce unusual molecular conformations to maximize intramolecular interactions.
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