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) P41 (or P43),Z′ = 1; (2) Pca21, Z′ = 2; (3) P, Z′ = 4; (4) P21/n, Z′ = 1; (5) P41212 (or P43212), 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.