Electron spin resonance studies of iron(III) complexes of ethylenediaminetetra-acetate and N-(2-hydroxyethyl)ethylenediamine-NN′N′-triacetate in co-ordinating solvents

Abstract

Remarkable solvent dependence of the apparent peak-to-peak linewidth (ΔHpp) has been observed for the rhombic type of e.s.r. spectra of the high-spin FeIII(edta)(edta = ethylenediaminetetra-acetate) and FeIII(hedta)[hedta =N-(2-hydroxyethyl)ethylenediamine-NN′N′-triacetate] complexes in a series of co-ordinating solvents. Moreover, the order of the solvents which gave the characteristic ΔHpp for each complex was different for the two complex systems: i.e. H2O dimethyl sulphoxide (dmso) > NN-dimethylformamide (dmf) > CH3OH for FeIII(edta) and H2O > CH3OH > dmf dmso for FeIII(hedta). Solvent dependence of the band maxima (λmax.) corresponding to the d–d transition has been also observed for the same series of iron(III) complex–solvent systems although the λmax. values obtained were less sensitive to the solvent than the ΔHpp values. In this case, the solvent dependence of λmax. for FeIII(edta) and FeIII(hedta) was similar: λmax. was smaller for H2O and CH3OH (<600 nm) than for dmf and dmso (>700 nm). The co-ordination behaviour of the solvent molecules to these iron(III) complexes is discussed in relation to both the ΔHpp and λmax. values. It is revealed that in the case of rhombic high-spin iron(III) complexes wit such edta and hedta, ΔHpp values obtained by e.s.r. spectroscopy reflect small changes in the co-ordination circumstances; λmax. values obtained from electronic spectra did not.