Investigation of Chloride Binding Abilities of Symmetric Squaramides

In this work, three symmetric squaramide derivatives were synthesized, and their anion-binding properties were systematically investigated. The binding properties of squaramides I–III with anions were determined by spectroscopic titration in DMSO-d6 using tetrabutyl ammonium salts. During titration with ammonium salts, the shift values of the protons of NH groups in the squaramide structure were recorded in 1H NMR. The variations in the chemical shifts of NH protons in the squaramides were analyzed with the DynaFit and BindFit programs to obtain the corresponding association constants. The greatest chemical shift was obtained from TBA-Cl with squaramide I titration, and it has the highest binding capacity with squaramide I and Cl– anion. Therefore, it was found that both the number of CF3 groups on the aromatic ring and the number of CH2 groups between the aromatic ring and the amide moiety in the structure of squaramide influence the strength of the anion binding ability. The stoichiometry of complexation between squaramides I–III and Cl– was also investigated using Job’s plots.