Preparation and properties of some metal complexes with water soluble calixarenes

Water-soluble sodium hydroxycalix[n]arene-p-sulfonates(Na_n1_n, n=4, 6 and 8), which were prepared by introducing the sulfonic acid groups into the p-positions of the hydroxyl groups of calix[n] arenes, behaved as a metal ligand even in the acidic solution and formed slightly soluble metal complexes in water with rare earth-, alkali earth- and some other metal ions, such as zirconium(IV), hafnium(IV) and thorium(IV). The composition of the metal complexes with rare-earth metal ions (Ln³⁺) was found to be NaLn1₄·mH₂O(m=7 - 14), Ln₂1₆·mH₂O(m=17 - 40) and Ln₂H₂1₈·mH₂O(m=14 - 35), respectively, by the elemental analyses and IR spectra. The effects of the molar ratio of the metal ion to the ligand and the presence of the coexisting anions in the reaction mixture upon the yield of the complex also supported the above composition and indicated that the metal ion in the complex is bound with sulfonate groups of the ligand molecule forming the sulfonate chelate like a salt in property. A series of alkali earth metal ions(M²⁺) such as Ca²⁺, Sr²⁺ and Ba²⁺ also formed metal complexes having the similar molecular formulas, M₂1₄·mH₂O(m=5 - 10), M₃1₆·mH₂O(m=5 - 22) and M₄1₈·mH₂O(m=6 - 20), respectively. On the other hand, tetravalent metal ions such as Zr(IV), Hf(IV) and Th(IV) formed the complexes in which both sulfonate groups attached at the upper rim and deprotonated hydroxyl groups attached at the lower rim of the ligand coordinated to a metal ion in the complex.