Supramolecular self-assembly and thermodynamic properties of 5-aryl-1-(1,1-dimethylethyl)-1H-pyrazoles in the crystalline state

Abstract A series of seven 5-aryl-1-(1,1-dimethylethyl)-3-trifluoromethyl-1H-pyrazoles [in which aryl: C6H5 (1); C6H4-4-F (2); C6H4-4-Cl (3); C6H4-4-Br (4); C6H4-4-I (5); C6H4-4-CH3 (6), C6H4-4-OCH3 (7)] and 5-aryl-1-(1,1-dimethylethyl)-1H-pyrazole [C6H4-4-NO2 (8)] was studied at the molecular and supramolecular level. X-ray diffraction, thermal analysis, sublimation enthalpy data, NMR spectroscopy, and DFT calculations were used in this systematic study. The supramolecular cluster was used as demarcation and furnished energetic and contact area data of each compound, which allowed proposals of crystallization mechanisms. Two different mechanisms were observed: (i) compounds 1–4 had 2 stages, where initially the monomers formed a 2-D block, followed by the formation of the 3-D block; (ii) compounds 5–8 also had 2 stages, where initially the monomers formed a 1-D block, followed by formation of the 3-D block. The packing observed in the crystal was corroborated by data from 1H NMR experiments. The types of interactions observed were evaluated using Hirshfeld surface and QTAIM analysis and showed slight differences in both methods. Lastly, energetic and topologic data obtained from the clusters were correlated with crystal properties such as crystal packing efficiency, sphericity, and sublimation enthalpy and presented good trends between data.