Abstract
1,3-Di(2-pyridylmethoxy)-p-tert-butyldihomooxacalix[4]arene-crown-6 (2) was synthesized for the first time. 2 was isolated in a cone conformation in solution at room temperature, as established by NMR spectroscopy (1H, 13C and NOESY). Complete assignment of both proton and carbon NMR spectra was achieved by a combination of COSY, HSQC and HMBC experiments. The binding properties of ligand 2 towards alkali, alkaline earth, transition and heavy metal cations have been assessed by phase transfer and proton NMR titration experiments. The results are compared to those obtained with other dihomooxacalix[4]arene-crowns-6 and closely-related calix[4]arene-crown derivatives. 2 shows a preference for the soft heavy metal cations (except for Cd2+), with a very strong affinity for Ag+. Some transition metal cations are also well extracted. 2 forms 1:1 complexes with K+, Ca2+ and Ag+, and 1H NMR titrations indicate that they should be encapsulated into the cavity defined by the crown ether unit and by the two pyridyl pendant arms. A 1:2 (ML2) complex is formed with Zn2+ and two species, probably 1:1 and 1:2 complexes, are obtained with Pb2+.
Published Version
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