Using the Hirshfeld surface to investigate crystal packing in polymorphs and crystals with Z' > 1
Joshua McKinnon
and Mark Spackman
Chemistry, School of Biological, Biomedical and Molecular Sciences, University of New England, Armidale, NSW 2351, Australia (jmckinn4@une.edu.au)
Understanding the differences in the crystal
packing of molecules in polymorphic structures, or differences in the
crystalline environment of the unique molecules in crystals with Z' > 1.0 can be extremely difficult,
particularly when packing differences are subtle.
We have previously shown that the Hirshfeld surface of a molecular crystal offers a remarkable new way of exploring packing modes and intermolecular interactions in molecular crystals using a novel partitioning of crystal space[1]. Because these surfaces are most effectively utilised in the laboratory where access to interactive molecular graphics is available, we have also devised a two-dimensional mapping, called a 2D fingerprint plot, which quantitatively summarises the nature and type of intermolecular interaction and presents this information in a convenient colour graph[2].
We have found that the combination of the Hirshfeld surface and 2D
fingerprint plot for a molecule in a crystal provides a particularly powerful
tool when attempting to investigate subtle differences where a molecule exists
in different crystallographic environments. Here we present two detailed
examples - three polymorphs of
p-dichlorobenzene, and two polymorphs of
tetrathiafulvalene (TTF), one of which which contains four unique molecules.
1
McKinnon, J. J., Mitchell, A. S.,
Spackman, M. A. (1998) Chem. Eur. J. 4, 2136-2141; McKinnon, J. J., Mitchell, A. S., Spackman, M. A.
(1998) Chem. Commun. 2071-2072
2
Spackman, M. A., McKinnon, J. J.
(2002) CrystEngComm, 4, 378-392