Similaridade de estruturas supramoleculares em cristais orgânicos: proposta de índices quantitativos

Abstract

This investigation reports the proposal of a new method to obtain quantitative indexes of similarity in crystals, using the supramolecular cluster as study demarcation. A series of tert-butyl pyrazoles were used as models for the proposal and application of the indexes. The indexes (IX) consider geometric (ID), contact area (IC) and stabilization energy (IG) parameters. In addition, a multiparameter index of similarity (IDCG) was proposed – in which the inheritance of the initial parameters is carried – to aid in the comparison between structures with only one final value. It was observed that the demarcation problem, in relation to the size of the studied system, is one of the problems in studies of supramolecular similarity. It was possible to establish a similarity range for the proposed indexes, where IX ≥ 0.80 (high similarity); 0.80 > IX > 0.60 (intermediate); IX < 0.60 (low), where X = D, C, G or DCG. It was observed that two highly similar systems must have an isostructural, isotopological and isoenergetic behavior. Similarity indexes were applied in a series of polymorphs, with different numbers of molecules in the asymmetric unit. It was determined different regions of similarity within the polymorphism phenomenon, being possible to determine the boundaries between quasi-isostructural polymorphs. A new similarity index – based on the types and normalized contribution of the total intermolecular interactions of each cluster (IQ) – was proposed. The IQ indicates to be a versatile tool and applicable even for systems that do not share any similarity. In addition, mechanisms of crystallization of new polymorphs have been proposed. It was possible to indicate the time in which the different triazene polymorphs (1IA and 1IIA) are formed during the nucleation process. Similarity indexes were also applied for the bisphenyltriazenes, and mechanisms of crystallization were proposed to study the selfassembly of this series. The hydrogen interactions between the triazenes and the stacking are present in almost all examples at some point of crystallization process. It was possible to evaluate the unique characteristics of a pyridine solvate and to compare it with the structure without solvent. The IDCG was presented as a robust comparative index for all the comparisons, taking into account the particularities of the systems in its final value. The multilinear correlation indicated a high contribution of the energy parameter (43%) to the final value of the IDCG, followed by geometric (31%) and contact area (27%) parameters. Therefore, the IG is an indispensable parameter in the analysis of supramolecular similarity of crystalline structures.