Synthesis and binding properties of calix[4]arene diamide dicarboxylic acids

Calix[4]arenes diametrically substituted at the lower rim with two carboxylic acid and two tertiary amide binding groups were obtained in good yields and their acid-base properties studied in methanol solution. Complexation studies, performed in methanol by potentiometry, show that mononuclear (MLHz, z = 0, 1) or dinuclear (M2L) complexes are formed with alkali metal cations, whereas MxL2Hz (x = 1, 2, z = 0, 1) species, involving two ligands, are also present with alkaline-earth cations. Both ligands 2 and 3 show a remarkable selectivity for Ca2+ and Sr2+ among alkali and alkaline-earth metal ions