Cation complexation by chemically modified calixarenes. Part 10. Thioamide derivatives of p-tert-butylcalix[4]-, [5]- and [6]-arenes with selectivity for copper, silver, cadmium and lead. X-Ray molecular structures of calix[4]arene thioamide–lead(II) and calix[4]arene amide–copper(II) complexes

Abstract

The effect of chemical modification of the lower rim of p-tert-butylcalix[4]-, [5]- and [6]-arenes has been analysed with respect to cation binding by thioamide podands. Extraction data for metal picrates from water into dichloromethane are discussed. Cu^II, Pb^II and Ag^I ions are extracted efficiently by all the thioamides studied, whereas extraction of Cd^II only reaches significant levels with the pentamer derivative. Unlike their calixarene amide counterparts, these thioamides have no affinity in extraction for either alkali or alkaline earth metals. The X-ray molecular structure of a thioamide–Pb^II(ClO₄)₂ complex and, for comparison, that of an amide–Cu^II(ClO₄)₂ complex have been determined. Both complexes exist in the cone conformation with the metal ion encapsulated by the heteroatoms on the lower rin. The crystal structure of the lead complex derivative 5·Pb(ClO₄)₂·EtOH·0.5 H₂O, was solved by Patterson methods and refined by block diagonal least-squares analysis. The crystals are triclinic, space group P, a = 13.394(6), b = 13.459(6), c = 26.711(4) Å, a = 78.33(2), β = 87.62(2), γ = 60.46(2)° with R = 0.108 for 4417 observed reflections. The Pb²⁺ is bonded to the four ethereal oxygen and four thiocarbonyl sulfur atoms, [Pb–O, 2.65(2) to 2.72(2), mean value 2.68(3) Å; Pb–S, 2.82(1) to 2.95(1) with a mean of 2.91(3) Å]. The crystal structure of the copper calixarene complex 2·Cu(ClO₄)₂·H₂O ·1.4CH₃OH·EtOH, was solved by direct methods and refined by block-diagonal least-squares methods. The crystals are tetragonal, space group P4/ncc a = 17.147(2), c = 28.054(4) Å, with R = 0.079 for 1482 observed reflections. The Cu²⁺ resides on a four-fold axis and is bonded to the four carbonyl oxygen atoms [Cu–O, 1.926(6) Å]. Four ethereal oxygen atoms are at a distance of 2.963(6) Å from the metal ion.