Unraveling structure-property relationships in pseudopolymorphic 3,3′-(4-amino-1,2,4-triazol-3,5-diyl)diphenol: Insights from advanced crystallographic analysis (Hirshfeld surfaces, Energy frameworks), thermal behavior, and luminescent properties

Pesudopolymorphism/polymorphism significantly impacts the physical properties of crystalline materials, making the discovery and characterization of new pesudopolymorphs/polymorphs crucial for material science. This study aimed to characterize a newly discovered pseudopolymorph of 3,3′-(4-amino-4H-1,2,4-triazole-3,5-diyl)diphenol ( β- 3OH ) obtained from ethanol crystallization, compare its structural and physicochemical properties with the known methanol-derived polymorph ( α - 3OH ), and determine their relative stability. The novel β- 3OH was characterized using single-crystal X-ray diffraction (SCXRD), infrared (IR) spectroscopy, ultraviolet-visible (UV–vis) spectroscopy, powder X-ray diffraction (PXRD), and differential scanning calorimetry (DSC). Hirshfeld surface analysis and energy framework calculations were employed to understand intermolecular interactions and lattice energies. SCXRD revealed β- 3OH crystallizes in the monoclinic I 2 / a space group. Structural analysis showed different hydroxyl group orientations and molecular conformations ( cis/trans isomers) compared to α - 3OH . β- 3OH exhibited a higher luminescent emission maximum (428 nm vs. 414 nm for α - 3OH ). Hirshfeld surface analysis correlated larger stacking distances and phenyl-triazole dihedral angles in β- 3OH with specific C⋯H/C⋯C contacts. DSC data and fusion rules determined β- 3OH shows a monotropic relationship. Energy framework calculations demonstrated significantly stronger intermolecular interactions (electrostatic, dispersion, polarization, repulsion, total) in β- 3OH . Comprehensive characterization confirms the successful isolation of a new pseudopolymorph, β- 3OH . The combined structural, spectroscopic, thermal, and computational analyses consistently demonstrate that β- 3OH is thermodynamically more stable than α - 3OH , attributed to its enhanced network of intermolecular interactions. Pseudopolymorphs and polymorphs serve as crucial mediators in determining the physical characteristics of compounds. A new pseudopolymorph of 3,3′-(4-amino-4 H -1,2,4-triazole-3,5-diyl)diphenol ( β -3OH ) was obtained from ethanol. Single-crystal X-ray diffraction analysis shows that β -3OH belongs to the monoclinic system with the I 2 /a space group. There are two distinct cis -isomers and trans-isomer molecules in the crystal-structure of 3OH , where hydroxyl hydrogen-atoms exhibit the back-to-back, head-to-head and head-to-tail patterns. The luminescent maxima of β - 3OH are obviously higher than that of α - 3OH . The results of single-crystal X-ray diffraction analysis show that the stacking distances and the dihedral angles between phenyl and triazole rings in β - 3OH are higher than those found in α - 3OH , which are in line with the C∙∙∙H and C∙∙∙C intercontacts calculated by the Hirshfeld surface analysis. The results of energy frameworks reveal that β- 3OH is more stable comparison to α -3OH . • One novel pseudopolymorph of 4-amine-1,2,4-triazole have been obtained. • Their pseudopolymorphs can be modulated by the solvents. • β- 3OH is more stable comparison to α -3OH . • Several energies of β- 3OH are stronger than those of α -3OH . • The luminescent maxima of β - 3OH are obviously higher than that of α - 3OH .