Conformational polymorphism in a heteromolecular single crystal leads to concerted movement akin to collective rack-and-pinion gears at the molecular level
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Edited by Jack Halpern, University of Chicago, Chicago, IL, and approved December 12, 2007 (received for review June 29, 2007)
Abstract
We describe a heteromolecular single crystal that exhibits three reversible and concerted reorganizations upon heating and cooling. The products of the reorganizations are conformational polymorphs. The reorganizations are postulated to proceed through three motions: (i) alkyl translations, (ii) olefin rotations, and (iii) rotational tilts. The motions are akin to rack-and-pinion gears at the molecular level. The rack-like movement is based on expansions and compressions of alkyl chains that are coupled with pinion-like 180° rotations of olefins. To accommodate the movements, phenol and thiophene components undergo rotational tilts about intermolecular hydrogen bonds. The movements are collective, being propagated in close-packed repeating units. This discovery marks a step to understanding how organic solids can support the development of crystalline molecular machines and devices through correlated and collective movements.
Footnotes
- *To whom correspondence should be addressed. E-mail: len-macgillivray{at}uiowa.edu
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Author contributions: A.N.S. and L.R.M. designed research; A.N.S. and D.C.S. performed research; A.N.S., D.C.S., and L.R.M. analyzed data; and A.N.S. and L.R.M. wrote the paper.
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The authors declare no conflict of interest.
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This article is a PNAS Direct Submission.
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Data deposition: The atomic coordinates have been deposited in the Cambridge Structural Database, Cambridge Crystallographic Data Centre, Cambridge CB2 1EZ, United Kingdom [CSD reference nos. 641325 (Phase A), 641326 (Phase B), and 641327 (Phase I)].
- © 2008 by The National Academy of Sciences of the USA
