The 2D-fingerprint of the Hirshfeld surface represents a novel method for summarising the complex information contained in a molecular crystal structure into a single, unique full colour plot, which provides a 'fingerprint' of the intermolecular interactions in the crystal. Derived from the Hirshfeld surface, these 2D-fingerprint plots provide a visual summary of the frequency of each combination of de and di across the surface of a molecule, so they not only indicate which intermolecular interactions are present, but also the relative area of the surface corresponding to each kind of interaction.
For each point on the Hirshfeld surface we determine both de and di. Each point on the 2D fingerprint plot corresponds to a unique (, ) pair, and the colour of each point corresponds to the relative area of the surface with that (, ) pair. Points on the plot with no contribution on the surface are left uncoloured, and points with a contribution to the surface are coloured blue for a small contribution through green to red for points with the greatest contribution. All fingerprint plots are coloured on the same relative scale, so some fingerprint plots (including naphthalene, right) do not have any red points.
Because Hirshfeld surfaces nearly fill the available space, so void spaces are small, these 2D fingerprint plots are pseudo-mirrored along the de = di diagonal. Features along the diagonal occur due to like···like contacts (H···H contacts in naphthalene), while the 'wings' on the naphthalene plot are due to the C-H··· interaction.