W0049

Hirshfeld Surfaces: A New Tool For Visualising And Exploring Molecular Crystals. M.A. Spackman, J.J. McKinnon & A.S. Mitchell, Division of Chemistry, University of New England, Armidale NSW 2351, Australia

A remarkable new way of exploring molecular crystals is afforded by smooth, non-overlapping molecular surfaces arising from a novel partitioning of crystal space. These molecular Hirshfeld surfaces, so named because they derive from Hirshfeld's stockholder partitioning [1], are constructed by partitioning space in the crystal into regions where the contribution from the electron distribution of a sum of spherical atoms for the molecule (the promolecule) exceeds the contribution from the corresponding sum over the crystal (the procrystal). They clearly reflect the proximity of nearest neighbours, and hence intermolecular interactions, in a novel visual manner, offering a hitherto unseen picture of molecular shape in a crystalline environment. Surface features characteristic of different types of intermolecular interactions can be identified, and Hirshfeld surfaces are remarkably different for different polymorphic forms of the same material.

The figure illustrates this for the [alpha] and [beta] forms of oxalic acid (left and right in the figure, respectively).

Applications of this new tool to a variety of molecular crystals will be presented, including 3D isosurface pictures as well as a number of quantitative measures of molecular size and global shape. Future utilisation of local descriptors such as curvature will also be outlined.

[1] F.L. Hirshfeld, Theor. Chim. Acta, 44, 129 (1977).