Solvent extraction of sodium and potassium ions by dicarboxylated calix[4]arenes

The extraction of sodium and potassium ions by 25,27-dicarboxymethyl-26,28-dimethoxy-5,11,17,23-tetra-tert-butyl calix[4]arene ((LH2)-H-I) in chloroform shows the formation of (MLH)-H-I and M2LI complexes (M = Na, K). In 1,2-dichloroethane, the (MLH)-H-I species are formed in the acidic pH range, while only the Na2LI species is found at high pH values. The corresponding extraction equilibrium constants K-11 (M) and K-21 (M) have been evaluated and show a selectivity in favour of Na+ as compared to K+, whatever the nature of the complexes. In chloroform, this selectivity is much more pronounced considering the 2:1 complexes: K-11(Na)/K-11(K)much less than K-21(Na)/K-21(K). The coexistence of 1:1 and 2:1 metal:ligand complexes is also shown in the extraction of sodium in 1,2-dichloroethane by the 25,27-dicarboxymethyl-26,28-dimethoxyethoxy-5,11,17,23-tetra-tert-butyl calix[4]arene ((LH2)-H-II), locked in the cone conformation. Structural data of the complexes are discussed on the basis of H-1-NMR spectra. In particular, for (LH2)-H-I, a conformational change from cone to partial cone upon metal complexation has been evidenced for the complexes (KLH)-H-I, K2LI and Na2LI.