Packing and Conformational Polymorphism in 1,2-Bis(aminocarbonyl(1-<i>tert</i>-butyl-1<i>H</i>-pyrazol-(3)5-yl))ethanes: Illuminating Examples of Highly Flexible Molecules
Geórgia C. Zimmer, Anderson B. Pagliari, Vanessa B. Solner, Manfredo Hörner, Hélio G. Bonacorso, Nilo Zanatta, Marcos A. P. Martins
Abstract
Insights into the occurrence of packing and conformational polymorphs and anhydrous/hydrate forms of 1,2-bis(aminocarbonyl(1-tert-butyl-1H-pyrazol-[3]5-yl))ethanes with the substituents R = Me (a), F-4-Ph (b), Cl-4-Ph (c), and Br-4-Ph (d) in positions 5 (1) and 3 (2) of the pyrazole rings are presented. In this series, two molecular forms were observed, linear and folded. Compound 1a revealed an illuminating and rare example of a highly flexible molecule with packing polymorphism. The molecular stacking and absence of NH···O═C interactions promoted polymorph growth. Structure 2a showed chains driven by NH···O═C bonds in the anhydrous form and closed dimers by water binding the molecules (NHamide···OHwt···C═Oamide) in the hydrate form. Two different forms were observed for conformational polymorph 2d (linear and folded). The folded form was about −10 kcal mol–1 more stable than the linear form, showing significant crystalline packing differences. This occurrence is attributed to the rotation of the amide groups through the NH···O═C bonds. The linear shape showed a higher stabilization energy for NH···O═C bonds and a cluster −6 kcal mol–1 more stable than polymorph 2dI. Compounds 1b–d and 2b-c also had their crystal growth proposed and features highlighted.