Determination of the number of unpaired electrons in metal-complexes. A comparison between the Evans' method and susceptometer results

1,4,8,11-Tetraazacyclotetradecane (cyclam) is widely known as an ideal ligand for chelating heavy metal ions such as Ni2+ and Cu2+. In this work, the consequences of chelation on the preference for high spin or low spin configuration were investigated for Fe3+, Ni2+, Cu2+ and Cr3+. Two methods were used to determine the number of unpaired electrons in the complex. First the dependence of magnetic susceptibility change of the crystalline powder as a function of temperature increase was measured. In the second case, the Evans' method was used to obtain information about the number of unpaired electrons in the dissolved complexes. In some cases, such as Fe3+ and Ni2+, a discrepancy between the results obtained with the two methods was noticed. The results are influenced by the geometry of the complex, the aggregation state and the dimensions of the ions.