Structural Diversity of Hydrogen-Bonded 4-Aryl-3,5-Dimethylpyrazoles for Supramolecular Materials

The 1H-pyrazoles have high versatility and ability to form hydrogen-bonded supramolecular materials. In this study, the thermal stability, fluorescence, and H-bonding ability of the studied 3,5-dimethyl-4-(4-X-phenyl)-1H-pyrazoles showed large differences depending on the terminal substituent. Supramolecular structures were analyzed using X-ray diffraction and Hirshfeld surface calculations. Compounds were found to arrange in different hydrogen-bonded structures, depending on the substitution at the para position of the phenyl ring (X = OCH₃, NO₂, NH₂). The methoxy-substituted compounds arranged in dimers through methanol bridges, the nitro-substituted compound formed supramolecular polymers or catemers, and the amino-substituted compound gave rise to a new structure based on a 2D hydrogen-bonded network.