Conformation and supramolecular assembly in an azo-azomethine-pyrazole hybrid: crystal structure, Hirshfeld surface and QTAIM analyses.

An azo-azomethine-pyrazole hybrid, namely, 2-({[3-tert-butyl-1-(4-nitrophenyl)-1H-pyrazol-5-yl]imino}methyl)-4-[(4-methylphenyl)diazenyl]phenol, C27H26N6O3, crystallizes as an extended donor-π-acceptor system that combines azo, azomethine and pyrazole fragments within an almost coplanar conjugated framework. Single-crystal XRD revealed two crystallographically independent molecules (M1 and M2) in the asymmetric unit (Z' = 2), with small conformational differences arising mainly from the orientation variations of the peripheral substituents. In both molecules, an intramolecular O-H...N(imine) hydrogen bond generates an S(6) motif that reinforces molecular planarity and π-electron delocalization. The crystal packing is dominated by heterogeneous M1...M2 contacts, whereas the homologous M1...M1 and M2...M2 interactions are comparatively less effective. C-H...O and C-H...N hydrogen bonds, complemented by π-related contacts, assemble the molecules into a three-dimensional supramolecular architecture. The Hirshfeld surface analysis identifies H...H, C...H/H...C, O...H/H...O and N...H/H...N contacts as the principal contributors to the intermolecular organization. A Quantum Theory of Atoms in Molecules (QTAIM) analysis confirmed the intramolecular O-H...N(imine) interaction through the corresponding bond critical point and associated topological descriptors and also confirmed that a secondary intramolecular C-H...N(imine) contact forms a nonplanar S(6) motif. The FT-IR, 1H NMR and mass spectrometric data support the proposed molecular structure. The combined crystallographic, Hirshfeld surface and QTAIM analyses demonstrate the co-operative influence of hydrogen bonding and weak noncovalent interactions on the conformational stabilization and supramolecular assembly of this conjugated azo-azomethine-pyrazole system.