Dicarboxylate anion receptors controlled by alkali metal ions

Abstract

Dicarboxylate anion receptors have been synthesized and can be separated into two classes. One class consists of urea units, 2a, 2b and 2c, and the other class contains a diazacrown ether unit and thiourea units, 4. Complexation studies of ligand 2a with various dicaboxylate anions such as oxalate, malonate, succinate, glutarate, adipate, pimelate, suberate and azelate were carried out by 1H NMR titrations. Ligand 2a was able to form 1:1 complexes with all dicarboxylate anions and the complex between ligand 2a and glutarate possessed the highest association constants. Complexation studies between ligand 4 and dicarboxylate anions by UV-vis titration showed a dramatic color change which could be detected by naked eyes. The complexes of ligand 4 and dicarboxylate anions were 1:1 stoichiometry and ligand 4 formed the most stable complex with adipate. The effect of sodium ion towards anion binding abilities of ligand 4 was also investigated. In the presence of sodium ion, association constants of ligand 4 and dicarboxylate anions were found to increase.