A Fe < sup > III < /sup > O < inf > 4 < /inf > N < inf > 2 < /inf > co-ordination sphere assembled via an enolate-imine-amide ligand. Effect of amide protonation on the redox behaviour and stereochemistry of the iron(III) centre

Abstract

The reaction of anhydrous FeCl3, acetylacetone benzoylhydrazone (H2L) and KOH (1:2:3 mole ratio) in methanol produced an iron(III) complex, [FeL(HL)] 1, the crystal structure of which was determined. Each ligand binds through enolate O, imine N and amide O atoms in meridional fashion. In the dianionic L both the enolic OH and the amide protons are dissociated, whereas in the monoanionic HL only the enolic OH is deprotonated. Addition of 1 equivalent of HClO4 to 1 in MeOH gave [Fe(HL)2]ClO4 2. Similarly reaction of 1 equivalent of KOH with 1 yielded K[FeL2] 3. All the complexes were characterized by analytical, spectroscopic, electrochemical and magnetic measurements. The metal centre in 1 is redox inactive. However, in cyclic voltammetric experiments 2 displayed FeIII → FeII reduction at -0.21 V and for 3 an oxidation at 0.40 V (vs. saturated calomel electrode) was observed due to FeIII → FeIV oxidation. Magnetic moments (at 298 K) of the three complexes reflect a S = 5/2 spin state in each. The ESR spectra (at 298 K) of polycrystalline 1 and 2 are rhombic. On the other hand, an ideal axial spectrum was observed for 3.