For each crystal in the 11 CSP landscapes, we calculated the extent of parallel π -π stacking interactions for each molecule, expressed as a percentage per molecule. Aromatic rings within the molecule were only considered to be π-stacked if the intermolecular distance between the centre of the benzene rings did not exceed 5.5 Å, the angle between the benzene rings was within 0 • to 30 • , and the displacement between the centroids of the two benzene rings parallel to the plane of the rings was less than 2.0 Å.