Selective complexation of soft Pb2+ and Hg2+ by a novel allyl functionalized thioamide calix[4]arene in 1,3-alternate conformation: a UV-visible and 1H NMR spectroscopic investigation

Abstract

A new calix[4]arene, functionalized with two thioamide moieties and with two allylic groups at the lower rim and the upper rim, respectively, and fixed in the 1,3-alternate conformation has been synthesized and its complexing properties towards Pb²⁺, Hg²⁺, Cd²⁺ and Na⁺ have been determined by UV–Vis titrations and by ¹H NMR spectroscopy in organic media.

The stoichiometries of lead and mercury complexes (1 ∶ 1) were at first determined by the mole ratio method and by Job plots. The speciation of the two systems was obtained making use of two different multiwavelength and multivariate treatments of spectral data. The computer treatment of the data confirmed the 1 ∶ 1 stoichiometry for the two complexes and gave reliable values for the corresponding stability constants (log K_Pb = 7.7; log K_Hg = 7.8). The ligand shows a high selectivity for lead and mercury over cadmium and sodium ions which are not complexed at all.

Structural and conformational properties of the two complex species were obtained by ¹H NMR spectroscopy. ¹H NMR data show that, although having the same stoichiometry, the lead and mercury interact with the ligand molecule in a different manner.