Novel synthesis and evaluation of anion-π interactions in one-walled meso-cyanophenyl substituted calix[4]pyrrole (C4P): Experimental and computational insights

• Published in: Journal of molecular structure Vol. 1290; p. 135949
• Main Authors: Rather, Ishfaq Ahmad, Alam, Manawwer, Riaz, Ufana, Ali, Rashid
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.10.2023
• Subjects: Anion binding; Anion-π interaction; Calixpyrrole; Deep eutectic solvent (DES); Receptor; Anion binding; Anion-π interaction; Calixpyrrole; Receptor; Deep eutectic solvent (DES)
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2023.135949

•Synthesis and anion binding studies of meso-one walled cyanophenyl extended C4P have been described.•BindFit and DFT studies have revealed 1:1 anion binding stoichiometry.•Maximum anion binding affinity was observed in case of fluoride ion.•Conformational change from 1,3-alternate to cone in the presence of anion has been confirmed by 1H-NMR.•NH-hydrogen bonding and anion-π interactions cooperatively govern anion binding. A novel one-walled meso-cyanophenyl functionalized calix[4]pyrrole (4) was synthesized from cyanophenyl appended dipyrromethane (3) through conventional strategy and also by utilizing deep eutectic solvent of N,N'-dimethyl urea (DMU) & L-(+)-tartaric acid (TA) in a ratio of 7:3. The structural confirmation of 4 was done through 1H-NMR, 13C-NMR, FT-IR, and HRMS spectral data. Anion binding studies of the receptor 4 with several anions (halides, trigonal oxoanions, tetragonal oxoanions, etc.) used as tetrabutylammonium (TBA) salts, were successfully investigated by virtue of UV–Vis spectroscopy and time dependent density functional theory (TD-DFT). Notably, the UV–Vis absorbance titrations performed in CH3CN solvent, revealed significantly higher anion binding of receptor 4 with F¯, Cl¯, Br¯, and SCN¯ in comparison to the simple C4P. This can be ascribed to the fact that the cyanophenyl moiety is π-acidic in nature which participates in anion complexation through weak anion-π interactions (observed through 1H-NMR spectroscopy) and hence modulates anion binding through cooperative effect of preliminary NH-hydrogen bonding due to C4P scaffold and anion-π contacts due to cyanophenyl moiety. [Display omitted]