Hirshfeld surfaces34,35 and their corresponding fingerprint plots36 for EPI and derivatives were calculated using the Crystal Explorer37 software package. Hirshfeld surfaces offer a description of the electron density belonging to a defined unit (in this case molecules). Contrary to other types of molecular surfaces, Hirshfeld surfaces are defined by the molecule and the environment around it; the area enclosed within the surfaces presented here is defined as being where >50% of the electron density belongs to the selected molecule around which the surface is plotted. Two distances are defined for each point on the Hirshfeld isosurface: d e, the distance to the nearest nucleus outside the surface, and d i, the distance to the nearest nucleus within the surface. From these values, a normalized contact distance, d norm, can be defined relative to the van der Waals radii of the atoms involved, where d norm is either positive or negative depending on if the intermolecular contact distance is greater or less than the sum of the van der Waals radii.34 Plotting d norm on the Hirshfeld surface produces a surface with a red/blue/white color scheme; red areas correspond to contact distances shorter than the sum of the van der Waals radii, white areas approximately equal to the sum of the van der Waals radii, and blue areas where the distance is longer than the sum of the van der Waals radii (i.e. there are no close contacts). As plotting d norm on the Hirshfeld surface requires knowledge of the atom types associated with the values of d e and d i calculated at each point on the surface, it is possible to define the percentages of interactions to/from the surface arising from specific atom types. In this way, the Hirshfeld surface can be used to get information regarding types of intermolecular interactions occurring with a given molecule for which the surface is plotted.