Synthesis and crystal structure of (E)-3-tert-butyl-N-[(2-nitrophenyl)methylidene]-1-phenyl-1H-pyrazol-5-amine: a coplanar Schiff base with enhanced π-stacking interactions.

Abstract

The pyrazole-based Schiff base (E)-3-tert-butyl-N-[(2-nitrophenyl)methylidene]-1-phenyl-1H-pyrazol-5-amine, C₂₀H₂₀N₄O₂, was synthesized in a straightforward manner via a solventless maceration technique, and its structure elucidated through spectroscopic characterization and single-crystal X-ray diffraction analysis. The compound exhibits a degree of coplanarity, influenced by the ortho-nitro group on a phenyl ring. Crystal structure analysis, complemented by Hirshfeld surface analysis and QTAIM-C calculations, reveals that the crystal packing is mainly stabilized by a network of π-stacking and dispersion interactions. Notably, H...C π-stacking interactions, particularly those between ortho- and para-C-H atoms of phenyl groups, play a significant role in the packing motif. The Hirshfeld surface also reveals a 5.8% contribution from H...N contacts, involving aliphatic H atoms interacting with a pyrazole N atom. CE-B3LYP calculations highlight the dominance of dispersion forces in the crystal, with the strongest interaction energy calculated to be -58.9 kJ mol^-1 between the central molecule and the molecular pair related by the identity symmetry operation (x, y, z). These findings provide insights into the structure-property relationships of this compound and contribute to understanding crystal engineering principles for designing new materials.