Fig. 1. Statistical distributions for all $Z^{\prime }\le 5$ structures in the Cambridge Structural Database (CSD) composed of C, H and O atoms.

a Distributions of the minimum angle formed by the vectors e_i and n_c for $n_{\max }=5$. The 95% and 99% confidence intervals are within 3 degrees, suggesting a restriction in the orientation of the inertial eigenvectors related to the vector set n_c. b Distributions of the minimum angle formed by the vectors k_r, defined to be perpendicular to the average plane of the benzene rings, and n_c for $n_{\max }=5$. c The van der Waals (vdW) free volume as a fraction of the unit cell volume. d The molecular van der Waals volume (vdW)_mol as a fraction of the unit cell volume Ω for crystals with four molecules in the unit cell (Z = 4). e, f Distributions of the lengths of the C–H and O–H close contacts for contact length l ≤ (sum of vdW radii + 0.5)Å. The close contacts are characterized as line-of-sight contacts, for which the position vector connecting the two atoms does not intersect the vdW sphere of a third atom. The peak of the distribution for the line-of-sight contacts provide the optimal separation between the two atoms forming the contact. The distribution for the C–H contacts is characteristic of all contacts involving at least one C atom while the O–H distribution is characteristic of the contacts between a hydrogen and a highly electronegative atom. The presence of intermolecular hydrogen bonding creates a secondary peak characteristic of the optimal hydrogen bond length affecting the connectivity of neighboring molecules in the unit cell. Source data are provided as a Source Data file.