MONONUCLEAR, OLIGONUCLEAR AND POLYNUCLEAR IRON(III) COMPLEXES WITH POLYALCOHOLS FORMED IN ALKALINE AQUEOUS-MEDIA

Low molecular weight complexes of Fe(III) with selected diols, glycerol and sorbitol and their hydrolysis products in alkaline aqueous media have been prepared and characterized. The three types of ligands interfered distinctly different with hydrolysis. According to solubility measurements of Fe in the presence of the two monomethylethers of glycerol, deprotonated 1,2-diolato entities are bound to Fe(III) in strongly alkaline aqueous solutions. The magnetic susceptibility measurements and Vis spectra indicate the formation of a mononuclear glycerol complex at high base and ligand concentration (greater-than-or-equal-to 1M). At pH 12-13, the growth of polynuclear complexes was investigated by laser light scattering and by kinetic measurements of the rate of degradation in 2 M HCl. A monotonic increase of the hydrodynamic radius (11-40 angstrom) and half life (0.5-10 s) over a period of four weeks was observed. Polynuclear Fe(III)-sorbitol complexes have a pH-dependent molecular weight, hydrodynamic radius and half life of degradation, with a small low molecular weight complex (pH greater-than-or-equal-to 10.5) and a gel (pH greater-than-or-equal-to 7) as the extremes of the series. The polymerization of these Fe(III)-sorbitol complexes is completely reversible.