Crystallization Mechanisms Applied to Understand the Crystal Formation of Rotaxanes

Abstract

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.

Supramolecular Similarity in Polymorphs: Use of Similarity Indices (IX)

“…This result corroborates the behavior already observed in our previous study that proposed new descriptors, 16 and also when applied to some crystalline structures of rotaxanes. 23 The range of values for I D is somewhat narrow and indicates that the real minimum for this index should be somewhere between 0.6 and 0.7. Once again, this demonstrates that for a quantitative comparative index the sole use of the geometric parameter has its limitations.…”

“…Recently, these indices have been used to compare crystalline structures of [2]rotaxanes. 23 The normalized data used allow the results to be compared between distinct crystalline structures. A multiparameter index (I mp ) was shown to be a quantitative index to assess the contribution of more than one considered parameter, e.g., a multiparameter index using geometry and contact area will be I DC .…”

π-Stacking Stopper-Macrocycle Stabilized Dynamically Interlocked [2]Rotaxanes

“…To verify the intercomponent stabilization [ 52 , 53 , 54 , 55 , 56 , 57 ], rotaxanes with stronger π-stacking interaction were synthesized. Dialdehyde 1 was selected due to its conjugated aromatic structure.…”

[2]Rotaxanes Bearing a Tetralactam Macrocycle: The Role of a Trifurcated Hydrogen Bond in the Crystalline State

“…The interaction stabilization energies of each "furcated" system were obtained using the G AI analysis, following a procedure already reported in studies using different kind of molecules. [4,10,12,14,[23][24][25][26] The G AI analysis furnished the energy of each atom···atom interaction correlating Quantum Theory of Atoms in Molecules (QTAIM) data and intercomponent stabilization energy. The QTAIM provides a quantum description of the location and behavior of the atoms in a chemical bond.…”

“…In the past, the problem resided in obtaining crystals, and today, the difficulty lies in understanding how to systematically study the number of structures available. [2] Therefore, the search for approaches that investigate interactions in rotaxanes, especially in the crystalline state, presents a continuous challenge as this may lead to a significant impact in designing systems with desired properties, [3,4] which are mainly affected by several intercomponent interactions. Nevertheless, there is a lack of studies in the literature regarding these interactions in the crystalline state.…”