A Magnetic Study of the Iron(III) Complexes of Polyols and Sugars in Aqueous Solution

Abstract

Abstract Plots of the effective magnetic moment (μeff) of the iron(III) ion against pH for aqueous iron(III) ion solutions of 1,2-ethanediol, 1,3-propanediol, glycerol, d-glucitol, d-fructose, two oligo-sugars, poly(vinyl alcohol) (PVA), and methyl cellulose at various concentration ratios of polyols or sugars to the iron(III) ion ([iron(III) ion] = 10.0 mM) at room temperature were obtained by the Gouy method. At low concentraion ratios, precipitation resulted at around neutral pH, where the concentration of polymers is expressed in terms of the monomeric residues. The pH range for precipitation became narrower as the ratio increased. However, the precipitates, once formed for the case of the former two diols, remained unchanged at any alkaline pH. During the course of the change in pH from 1 to 13, the μeff value in units of B.M. was initially ca. 6, but steeply decreased at around pH 2, and then leveled off at a constant value of ca. 3.6 in the pH range 3 to 10. It gradually rose to a value of 5–6 beyond pH 10 for the cases of glycerol, d-glucitol, and sugars. This fact, together with the ESR data obtained here, indicates that iron(III) ions exist as usual hydrated ions at pH 1–2, as some cluster like Fe(OH)3 at pH 3–10, and mostly as mononuclear ions coordinated to the alcoholic OH groups at a stronger base pH.