Magnetization Measurements on Iron (III)Solutions for Detecting Oligomer Formation

Abstract

By measuring the magnetization at low temperatures (near 1 K) and intense magnetic fields ( ≳100 KG), information about oligomer formation in ferric salts solutions can be obtained. It is shown that, under rather general conditions, the magnetic moment per ferric ion of a given ferric solution measured in the saturation regime should be equal to 5 β if all the complexes involved in the solution are high-spin monomers. Moreover, if the solution is mainly composed by monomeric species and antiferromagnetic dimers, the relative concentration of monomeric and dimeric species can easily be determined. This techniques has been applied to solutions of Cl3Fe and (NO3)3Fe9H2O in isopropanol as solvent containing about 0.4 M of water. In the first case the present measurements are consistent with the existence of dihydroxo ferric dimers suggested by previous Mössbauer and Optical Absorption data. The relative concentration of these dimers increases from 25% to 50% when the water content increases from 0.4 M to ~ 10 M. In the second case it is confirmed that the solution is mainly composed by oligomers, the relative concentration of monomeric species being less than 30%.