The present study discusses the crystalline packing formation of several [2]rotaxanes with Leigh‐type tetralactam macrocycle bearing different threads. The presence of solvent molecules in some structures are also addressed to shed some light on this matter. Additionally, the degree of similarity between supramolecular structures of rotaxanes was discussed using similarity indices. For this, new descriptors and crystallization mechanisms, which were proposed in terms of contact area and stabilization energy, were carried out to evaluate the rotaxane molecules. It was possible to observe similar general stages of crystallization dominated by the formation of 1D‐blocks and, in fewer cases, by dimers in the first stage of nucleation. The preference for the formation of 1D nuclei resides in the large contact area and complementarity involved in the large set of interactions between the rotaxanes at the earliest stages of crystallization. In this context, it was possible to propose when solvent molecules are trapped between the rotaxanes during crystal formation. Therefore, a unique example of a rotaxane whose topology favored the entrapment of water molecules between rotaxanes during the first stage of the crystallization process is presented. Crystallization mechanisms showed to be a valuable asset in the supramolecular investigation of rotaxanes in the crystalline state.

Bis-ureas are generally associated with strongly bifurcated hydrogen bonds (NH···OC interactions). For this reason, a series of trisubstituted bis-ureas (TBU) with bulk substituents were designed and used as a study model to gain a better understanding of the persistence of NH···OC interactions as driving interactions of the crystallization process. The TBU molecules possess different substituents (isopropyl, benzyl, and 4-nitro-benzyl) and variations in the methylene spacer. The TBU self-assembly, through crystallization mechanism proposals, is discussed related to the role of intermolecular interactions that drive and participate in the crystallization process. The intermolecular interactions present in the proposed first nuclei of crystallization were studied by concentration-dependent 1H NMR experiments and QTAIM analysis. Our findings showed that even with bulky substituents, the NH···OC interactions in most compounds played an important role in stabilizing the first nuclei formed during the crystallization process. However, in one case the molecular topology prevented the formation of NH···OC as the driving interaction in the first crystallization nuclei. In this case, the crystallization was mainly governed by a set of “weaker” interactions, showing that a subtle molecular change in the methylene spacer favored H···H interactions over directional N–H···O interactions. For some of the compounds studied, we propose both when the symmetry-independent molecules observed in the crystal lattice could be formed and when the water molecules are probably trapped during the crystallization to form the hydrate crystalline phases. This study contributes to the better understanding of issues related to modulating NH···OC hydrogen bonds using bulky substituents in the self-assembly of flexible TBU molecules.

This study investigated the proper classification and quantification of intercomponent trifurcated hydrogen bonds, in the crystalline state, of rotaxanes bearing a tetralactam Leigh‐type macrocycle. Quantum mechanical calculations were carried out to obtain the interaction paths and their stabilization energies. In general, the use and necessity of fragmentation in types of interaction have been reported in the literature, although they are commonly performed only using a geometric approach. This results in N–H···O interactions that are indicated as the main interactions between components, neglecting other possible interactions. The use of energetic fragmentation was demonstrated here under an appropriate demarcation considering all interactions and showing the existence and role of the C–H···O interaction. The C–H···O interactions showed similar energy to N–H···O interactions with average values around –4.75 kcal mol–1 and –4.60 kcal mol–1, respectively. This revealed that the three hydrogen bonds are part of a cooperative set of interactions with a similar contribution. The trifurcated hydrogen bonds presented high contribution in the total intercomponent stabilization energy of the rotaxanes, with an average value of 51 % in the studied series.

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Understanding the nature of the mechanical bond is critical to advancing the design of novel mechanically interlocked molecules. Given that numerous applications of new materials are related to solid-state properties, the behavior of the mechanical bond in the crystalline solid state is a key issue to be explored. Hence, this study sought to address how the freedom degree of the interlocked components can promote the formation of different crystalline phases. A series of rotaxanes substituted with different halogen atoms in the same position of the macrocycle were chosen as the model for study. Crystallization experiments were carried out in different solvents, obtaining 15 crystalline phases for the five studied compounds. The intercomponent interactions were evaluated in solution through variable-temperature 1 H NMR experiments and in the crystalline solid state through quantum mechanics calculations. All rotaxanes presented the same type of interaction in solution and the solid state, although the distribution of interaction energies was modified depending on the crystalline phase. Selecting the substituent at the macrocycle and using different crystallization solvents at different temperatures formed these different crystalline phases. At the supramolecular crystalline level, four similar comparisons were found correlating the different compounds, in which one was the anhydrous phase and the other three phases were solvates of chloroform, tetrahydrofuran, and toluene. The key to understanding the formation of the different crystalline forms is the presence of the mechanical bond, providing the flexibility and mobility of the entwined components for keeping the most favorable intermolecular interactions in each experimental condition assayed.