The crystallization of a series of 1-(4-halophenyl)-3-phenyltriazenide N1-oxides (1–4) and 1-(phenyl)-3-phenyltriazenide N1-oxide (5) was evaluated using the supramolecular cluster approach. This method is an efficient tool to assess the crystallization mechanism of compounds and, consequently, the steps involved in crystal formation. Compounds 1 and 4 show crystallization in two main steps while compounds 2 and 3 present three main steps, in which column formation occurs in the first step. The crystallization process for 5 occurs in 3 main steps, starting from a robust dimer formation (−16.82 kcal mol⁻¹). Two new parameters – N_CG% (topological and energetic contribution percentage) and NG/NC (energetic parameter/topological parameter ratio) – assisted in the interpretation of crystal growth. Compounds 1–4 showed N_CG% = 50 in the first step while compound 5 reached only 50% of the contribution in the second step. The differences in N_CG% were attributed to strong hydrogen bonds in the non-halogenated compound. The dominant parameter in each step of the crystallization process was indicated by the NG/NC parameter. The crystallization mechanism in all compounds was initially driven by an energetic process followed by a topological process. The existence of X⋯π interactions was shown and was observed to be a consequence of a topological process and without any major contributions to crystal formation. Thermal analysis and UV-vis spectral data were also discussed regarding the properties of these compounds.

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)-1H-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).

The crystal structures of dicationic ILs [DBMIM][2BF₄] (1) and [DBMIM][2Br]·[2H₂O] (2) were investigated in order to explore the intermolecular interactions in these compounds. An energetic and topological approach for characterization of supramolecular clusters in organic crystals was used. The study of the crystals was done by considering the stabilization energy and topological properties such as contact surfaces and energy content between cations and neighboring anions (supramolecular clusters). The study showed that: 1 is auto-organized into layers (one-dimensional structure) by an anion–cation interaction (weak electrostatic and ionic), and the three-dimensional supramolecular structure of 2 is constructed through simultaneous interactions between cations, anions, and water molecules. This network results in interaction chains in two different directions. Additionally, the supramolecular cluster approach allowed evaluation of the participation of the topological component during the formation of the crystals of 1 and 2. Among the different types of interactions proposed, the most predominant was the one classified as type III, which has small and medium energy values, and a medium-sized contact surface. The thermal and morphological properties were also studied to further characterize these materials and to better understand the resulting structure–property relationships.

A series of seven N-phenylamides [R–C(O)NHPh, in which R: CH₃, C(CH₃)₃, Ph, CF₃, CCl₃, CBr₃, and H] were used as models in this study. Molecular packing and intermolecular interactions were evaluated by theoretical calculations, solution NMR, and quantum theory of atoms in molecules analyses. Crystallization mechanisms were proposed based on the energetic and topological parameters using the supramolecular cluster as demarcation. Concentration-dependent ¹H NMR experiments corroborated the proposed interactions between molecules. For all compounds (except for R: H, which initially formed tetramers), layers (two-dimensional) or chains (one-dimensional) were formed in the first stage of the proposed crystallization mechanisms. The presence of strong intermolecular NH···O═C interactions promoted the first stages. The study in solution provided different values of association constant (K_ass) governed by the hydrogen bond NH···O═C, showing that the stronger interactions are directly influenced by the substituent steric hindrance. A correlation between K_{ass(NH···O═C)} from the solution and the NH···O═C interaction energy in the crystal showed a good trend.