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) P1̅, 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.

本研究借助赫希菲尔德表面（Hirshfeld surfaces）指纹图，定位并分析了用于测定1,8-二羟基蒽醌五种多晶型物相对能量的多种方法存在的缺陷。研究通过X射线晶体学（X-ray crystallography）表征了9个晶体学独立分子，并从X射线衍射结构中导出了赫希菲尔德表面。五种多晶型物（编号1至5）对应的空间群与独立分子数（Z′）如下：(1) P4₁（或P4₃），Z′=1；(2) Pca2₁，Z′=2；(3) Poverline{1}，Z′=4；(4) P2₁/n，Z′=1；(5) P4₁2₁2（或P4₃2₁2），Z′=0.5。经竞争溶解度实验验证，在可重现的晶体结构中，1号多晶型物的热力学稳定性最高，其次为2号与4号。本研究采用CVFF力场、COMPASS力场以及密度泛函代码SIESTA，对五种多晶型物的无约束结构进行了计算。