New chromogenic azocalix[4]arene podands incorporating 2,2′-bipyridyl subunits

Abstract

Six new calix[4]arenes 2, 3 and 4 functionalized with 2,2′-bipyridyl and azophenyl groups at the lower rim and the upper rim respectively have been synthesized and their complexing properties towards Zn²⁺ have been determined by UV-Vis titrations in organic media. The conformational properties of these ligands were obtained by ¹H NMR spectroscopy. The stoichiometries of zinc complexes were determined by both the mole ratio method and Job plots. A stoichiometry of 1∶1 was found for the complexes Zn-2 and Zn-3 and 1∶2 for the complex Zn-4 as a function of the number of grafted bipyridyl groups. The association constants for 1∶1 complexes were determined by using the Benesi–Hildebrand plot and also by linear regression analysis.