A (FEO4N2)-O-III COORDINATION SPHERE ASSEMBLED VIA AN ENOLATE-IMINE-AMIDE LIGAND - EFFECT OF AMIDE PROTONATION ON THE REDOX BEHAVIOR AND STEREOCHEMISTRY OF THE IRON(III) CENTER

The reaction of anhydrous FeCl3, acetylacetone benzoylhydrazone (H(2)L ) 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 lig and binds through enolate O, imine N and amide O atoms in meridional f ashion. In the dianionic L both the enolic OH and the amide protons ar e dissociated, whereas in the monoanionic HL only the enolic OH is dep rotonated. 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 [FeL(2)] 3. All the complexes were characterized by analytical, spectr oscopic, electrochemical ana magnetic measurements. The metal centre i n 1 is redox inactive. However, in cyclic voltammetric experiments 2 d isplayed Fe-III --> Fe-II reduction at -0.21 V and for 3 an oxidation at 0.40 V (vs. saturated calomel electrode) was observed due to Fe-III --> Fe-IV oxidation. Magnetic moments (at 298 K) of the three complex es 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 axia l spectrum was observed for 3.