Complex formation of lanthanum(III) or cerium(III) with 3-aminomethylalizarin-n.n-diacetic acid and fluoride

Abstract

The complex formation in aqueous solution of lanthanum(III) or cerium(III) with 3-aminomethylalizarin-N,N-diacetic acid (alizarin complexan, L) and fluoride (F) was studied by spectrophotometry. At pH 4.50 the metals react with alizarin complexan to form the compounds LaL or CeL; the conditional constant of LaL is 3.6·10 4. At pH 5.50 and 6.50 both systems contained a mixture of the 1:1 species with complexes containing two or more metal ions per ligand molecule. The ternary metal-alizarin complexan-fluoride systems were studied by recording absorption and continuous variations curves, and plotting theoretical curves of continuous variations for various ML-fluoride complexes. The results showed that the ternary complexes have the composition (ML) 2F 2, the conditional constant at pH 4.50 being 6.3·10 13 for the lanthanum complex. It is shown theoretically that ternary complexes of the form (ML) 2F 2 and (ML)F are characterized by having continuous variations curves with maxima displaced to higher mole fractions of the binary reactant. The differences between the curves for the two types are discussed. The ternary complex probably consists of a ring-formed dimer La 2L 2 with one fluorine atom attached to each of the two metal atoms.