The effect of chemical modification of the lower rim of p-tert-butylcalix[4]-, [5]-and [6]-arenes has beenanalysed 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 (ClO 4 ) 2 complex and, for comparison, that of an amide-Cu II (ClO 4 ) 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 5ؒPb(ClO 4 ) 2 ؒEtOHؒ0.5H 2 O, was solved by Patterson methods and refined by block diagonal least-squares analysis. The crystals are triclinic, space group P1 , a = 13.394(6), b = 13.459(6), c = 26.711(4) Å, a = 78.33(2), = 87.62(2), = 60.46(2)Њ with R = 0.108 for 4417 observed reflections. The Pb 2+ 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 2ؒCu(ClO 4 ) 2 ؒH 2 Oؒ1.4CH 3 OHؒEtOH, 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 Cu 2+ 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.Chemical modification of calixarenes 1 1,2 on the lower rim represents a simple though effective and versatile way of producing receptors with very selective cation binding properties. We and others have demonstrated complexation of alkali and alkaline cations using calixarenes with pendant ether, 3 ester, 4-9 ketone, 10 carboxylic acid, 11 amide, 12-15 crown ether 16 and hemispherand 17 groups attached to the calixarene substructure through the phenolic oxygen atoms. In some cases the selectivity and strength of complexation were sufficiently favourable to allow the incorporation of the calixarene into ion-selective electrodes 18 and ISFETS, 19 e.g. for Na + and Cs + ion. Alkaline earth salts are strongly bound by calixarene amides, the diethyl amide 1 in the tetramer series exhibiting a large preference in stability constant (ca. 10 8 ) for Ca 2+ over Mg 2+ in methanol. 13 Calixarene ring size is also important with the larger pentamer and hexamer derivatives favouring the larger cations. We have extended our research into chemically modified calixarenes to include systems with binding potential for metallic ions in other regions of the periodic table and we now describe the synthesis and complexati...

The cation complexing abilities of a series of p-tert-butylcalix[4]arenes bearing ligating ester groups in the cone conformation have been assessed by stability constant measurements in methanol and extraction studies from water into dichloromethane. The cations studied were Na+ and K+ and variations in the ester function (C0,R) included R = methyl, ethyl, n-butyl, tert-butyl, benzyl, p henyl, p henacyl, met hoxyet hyl , trif luoroet hyl, met hylt h ioet hyl and prop-2ynyl. The effect of replacing one or two ester functions in the tetraethyl ester by methyl ester, carboxylic acid, ketone and amide functions was also studied. Selectivities for Na' relative to K+ in stability constants range from 2 to 2500, the phenacyl derivative having the highest selectivity. X-Ray diffraction analysis was used to probe the conformation of the trifluoroethyl ester 11. Crystals of I 1 are monoclinic, space group P2,/n, in a cell of dimensions a = 13.987( 2), b = 16.194(3), c = 27.630(5) A; p = 98.70(1)"; R = 0.077 for 3172 observed data. The compound possesses a distorted cone conformation.

The following are summaries of seven of the papers presented at a Meeting of the Analytical Division held on July 16th-I7th, 1990, in ICI C and P Ltd., Runcorn, Cheshire.

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