Packing and Conformational Polymorphism in 1,2-Bis(aminocarbonyl(1-tert-butyl‑1H‑pyrazol-(3)5-yl))ethanes: Illuminating Examples of Highly Flexible Molecules

• Published in: Crystal growth & design Vol. 21; no. 8; pp. 4690 - 4706
• Main Authors: Zimmer, Geórgia C, Pagliari, Anderson B, Solner, Vanessa B, Hörner, Manfredo, Bonacorso, Helio G, Zanatta, Nilo, Martins, Marcos A. P
• Format: Journal Article
• Language: English
• Published: American Chemical Society 04-08-2021
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/acs.cgd.1c00541

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.