Characterization of the Complexes of Iron(III) with L-Tartrate in the Solvent Extraction System -Formation of Iron(III)-Cluster Complexes-

Abstract

The complexes of iron(III) with L-tartaric acid (hereafter abbreviated as iron(M)-tartrate complexes) formed in aqueous solutions at various pH values are extracted with (methyl)trioctylammonium chloride (TOMAC; R3R'NC1) in toluene. The complex species before and after extraction have been characterized by various techniques. A magnetic susceptibility titration experiment has shown that iron(III)-tartrate complexes in aqueous solution vary in structure accoriding to the conditions of pH and R=[L-tartaric acid]/[iron(III) ion] and are extracted with TOMAC into toluene from aqueous solution without great changes in structure. The complex species at R=1 (pH 6-12), R=3 (pH 3-12) and R=10 (pH 3-8)are of a type of iron(III) cluster complexes. It has been revealed that in aqueous solutions at R=3-10 the ratio of tartrate anion to iron(III) ion in the complexes are less than 2 and that this ratio decreases with an increase in pH. The estimated compositions of extracted complexes at R=3 (tart=tartrate anion) are as follows It is reasonably considered that the complex species at R=3 (pH10) bear a structural resemblance to ironan hydroxide clusters whose surfaces are modified with tartrate anions. Those negatively-charged carboxyl groups projecting to the outside can make ion-pairs with TOMAC cations and the complex species are extracted in toluene in such a form as reversed micelle. These complexes may be less than several tens Å in diameter.