Hirshfeld Surfaces Identify Inadequacies in Computations of Intermolecular Interactions in Crystals: Pentamorphic 1,8-Dihydroxyanthraquinone

Fingerprint plots of Hirshfeld surfaces were used to locate and analyze the deficiencies in various methodologies employed in the determination of the relative energies of five polymorphs of 1,8-dihydroxyanthraquinone. Nine crystallographically independent molecules were characterized by X-ray crystallography and Hirshfeld surfaces were derived from the X-ray structures. The space groups and number of independent molecules ( Z ′) for each of the polymorphs ( 1 − 5 ) is as follows: ( 1 ) P 4 1 (or P 4 3 ), Z ′ = 1; ( 2 ) Pca 2 1, Z ′ = 2; ( 3 ) P 1̅, Z ′ = 4; ( 4 ) P 2 1 / n, Z ′ = 1; ( 5 ) P 4 1 2 1 2 (or P 4 3 2 1 2), Z ′ = 0.5. Form 1 is the most thermodynamically stable among the reproducible structures, as established by competitive solubility tests, followed by 2 and then 4 . The unrestrained structures of the five polymorphs were computed using the CVFF and COMPASS force fields as well as with the density functional code, SIESTA.