The crystalline structures of carboxylic acid monolayers adsorbed on graphite

Bickerstaffe, A. K. and Cheah, N. P. and Clarke, S. M. and Parker, J. and Perdigon, A. and Messe, L. and Inaba, A. (2006) The crystalline structures of carboxylic acid monolayers adsorbed on graphite. Journal of Physical Chemistry B, 110 (11). pp. 5570-5575. DOI 10.1021/jp054798q

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Abstract

X-ray and neutron diffraction have been used to investigate the formation of solid crystalline monolayers of all of the linear carboxylic acids from C6 to C14 at submonolayer coverage and from C8 to C14 at multilayer coverages, and to characterize their structures. X-rays and neutrons highlight different aspects of the monolayer structures, and their combination is therefore important in structural determination. For all of the acids with an odd number of carbon atoms, the unit cell is rectangular of plane group pgg containing four molecules. The members of the homologous series with an even number of carbon atoms have an oblique unit cell with two molecules per unit cell and plane group p2. This odd−even variation in crystal structure provides an explanation for the odd−even variation observed in monolayer melting points and mixing behavior. In all cases, the molecules are arranged in strongly hydrogen-bonded dimers with their extended axes parallel to the surface and the plane of the carbon skeleton essentially parallel to the graphite surface. The monolayer crystal structures have unit cell dimensions similar to certain close-packed planes of the bulk crystals, but the molecular arrangements are different. There is a 1−3% compression on increasing the coverage over a monolayer.

Item Type: Article
Uncontrolled Keywords: 2006 AREP BPI IA49 IA52 2006 P
Subjects: 99 - Other
Divisions: 99 - Other
Journal or Publication Title: Journal of Physical Chemistry B
Volume: 110
Page Range: pp. 5570-5575
Identification Number: 10.1021/jp054798q
Depositing User: Sarah Humbert
Date Deposited: 16 Feb 2009 13:01
Last Modified: 23 Jul 2013 10:01
URI: http://eprints.esc.cam.ac.uk/id/eprint/145

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