Solvent and stoichiometry-dependent versatile organogelation and robust crystallization from the supramolecular association of adipic acid and triethanolamine

Abstract

Supramolecular self-assembly–directed two unique organogels were achieved by varying gel-immobilized solvents. One gel is comprised of adipic acid (ADP) and triethanolamine (TEA) in pure dimethylformamide medium (i.e., ADP-TEA-DMF), while the other is formed from the combination of adipic acid and triethanolamine in a 1 : 1 mixed solvent system of DMF and acetonitrile (i.e., ADP-TEA-DMF-MeCN). Furthermore, we observed robust crystallization behaviour under the different stoichiometric conditions of adipic acid with triethanolamine in pure dimethylformamide (i.e., Crystal-DMF) and in pure dimethyl sulfoxide (i.e., Crystal-DMSO). To evaluate the mechanical strength and viscoelastic attributes, rheological experiments were executed on these supramolecular organogels of ADP-TEA-DMF and ADP-TEA-DMF-MeCN. Additionally, comprehensive microstructural analyses were conducted in order to unravel the architectural variations arising from the involvement of different solvent-directed semi-solid gel-state. Scanning electron microscopy (FESEM) images of xerogel specimens obtained from the two organogels revealed distinctive morphological patterns. Notably, perceptible variations in the morphology were also observed in both the crystalline phases. The crystal structure of both the crystalline phases (i.e., Crystal-DMF and Crystal-DMSO) were explored using single crystal X-ray diffraction study at 296 K for Crystal-DMF and under liquid nitrogen atmosphere for Crystal-DMSO. Crystal-DMF and Crystal-DMSO have identical crystal structures that are composed of the adipate dianion (ADP²⁻) and the protonated triethanolamine (TEAH⁺). The crystal engineering pattern of Crystal-DMSO was elucidated through this study. These findings of versatile organogelation and robust crystallization emphasize the significance of solvent polarity and its diversity in attaining both the gel and crystalline phases. The organogel-formation strategy of ADP-TEA-DMF and ADP-TEA-DMF-MeCN was unravelled using infrared spectroscopic analyses. ESI-Mass spectral studies demonstrate the basic gel-constructing units, which are repeating to offer stable organogels. Thus, the solvent and the gelator concentration-directed organogelation process and the robust crystal-formation strategy are critically visualized in this study.