Insights on the Similarity of Supramolecular Structures in Organic Crystals Using Quantitative Indexes

Abstract

The quest for concepts of isostructurality in organic crystals has been long and mostly based on geometric data, even with the development of modern software. This field of study is of great interest to the pharmaceutical industry and for the prediction of crystal structures. Despite this, there is still no methodology that provides broad quantitative and comparable similarity data between two complete crystalline structures. The present study demonstrated that the similarity between two crystalline structures could be estimated from the similarity between the two “supramolecular clusters”. Quantitative indexes for similarity comparisons of crystal structures were shown using nine 5-aryl-1-(1,1-dimethylethyl)-1 H -pyrazoles as a model. This proposal includes the quantitative data of a geometric parameter ( I D ), a contact area parameter ( I C ), and an energetic parameter ( I G ). The proposed indexes exhibited good perspective regarding the similarity data and distinct regions of similarity. The range of similarity was set at I X ≥ 0.80, 0.80 > I X > 0.60, and I X ≤ 0.60 (X = D, C, or G). Indexes with a value near 1.0 indicate systems with isostructural, isocontact, and isoenergetic behavior. The results indicated that supramolecular structures with high similarity must have high values for all three indexes ( I D , I C , and I G ).

Crystallization Mechanisms Applied to Understand the Crystal Formation of Rotaxanes

“…The similarity indices for the supramolecular comparison between 5 and 6 furnished values of 0.74, 0.65, and 0.81 for I D , I C , and I G indices, respectively. These indices demonstrated that the molecular change mainly affected the geometric position and complementarity of the molecules when both systems were compared, this due the intermediate values of I D and I C .…”

“…In order to understand the similarity between two complete crystalline structures beyond qualitative comparisons, the recently proposed supramolecular similarity indices ( I X ) were applied. The indices use geometric ( I D ), contact area ( I C ), and stabilization energy ( I G ) parameters obtained by means of the supramolecular cluster . When the three parameters are combined is furnished a multiparameter index called I DCG , in which a single final value of similarity is furnished.…”

“…For this, new descriptors are discussed to evaluate rotaxane structures followed by the supramolecular investigation for the proposal of crystallization mechanisms. Additionally, supramolecular comparisons, which use similarity indices, will be discussed to evaluate the degree of similarity between supramolecular structures of rotaxanes.…”

Comment on ‘Solution growth and thermal treatment of crystals lead to two new forms of 2-((2,6-dimethylphenyl)amino)benzoic acid’ by R. Hu, Y. Zhoujin, M. Liu, M. Zhang, S. Parkin, P. Zhou, J. Wang, F. Yu and S. Long, RSC Adv., 2018, 8, 15459

“…Our rst questions regarding the new polymorph reported by Long et al 1 (Form II) relied on the supramolecular analysis of the supposed new polymorph and the earlier structure reported by Kovala-Demertzi et al 2 (Form I). Aer growing the supramolecular cluster [4][5][6] of both structures and applying an overlayby using the molecule M1 as referencehigh resemblance between the crystalline structures was observed. This indicated the possibility of being either the same crystalline structure (with a different renement) or the phenomenon of quasiisostructural polymorphism.…”

Intermolecular Interactions in Functional Crystalline Materials: From Data to Knowledge

“…The analysis of 42 tyrammonium salts demonstrated that isostructural cation packing can occur even with structurally different anions, with different hydration states and with different hydrogen bonding; realization of different packing was associated with various conformations of the ethylammonium group of the cation [110]. Martins, et al demonstrated that similarity between supramolecular clusters occurs only for molecules able to exhibit similarity in molecular shape-size parameters (thus called isostructural molecules), contact area, and energy of intermolecular interactions [111]. Fenamate co-crystals with 4,4'-bipyridine keep the packing arrangement of the initial solid connected by the 4,4'-bipyridine [112].…”