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

Abstract

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.

Completion of Crystallographic Data for the Series of 4-Halogenated-1H-pyrazoles: Crystal Structure Determination of 4-Iodo-1H-pyrazole and Spectroscopic Comparison

“…When N1 is protonated, pyrazole coordinates to metals through N2 as a monodentate ligand; however, N1 is readily deprotonated to form the pyrazolide ion, which can coordinate to metals in an exo-or endo-bidentate fashion in addition to monodentate coordination. The Lewis base tunability (via peripheral substitution) and structural rigidity of the pyrazole ligand led to its extensive applications in coordination chemistry [1][2][3], while the existence of both donor and acceptor sites in the same molecule enabled its role in supramolecular chemistry [4][5][6][7][8]. Pyrazoles can be substituted in the 3-, 4-, and 5-positions while maintaining the ability to form an N(H) .…”