Iron(III) complexes of N-Benzoyl-n′-salicylidenehydrazines: Synthesis, characterization and properties

Abstract

A series of iron(III) complexes of N-benzoyl-N′-salicylidenehydrazine and its substituted derivatives (H2bhsX; X = H, OMe, Cl, NO2) with the general molecular formula K[Fe(bhsX)2] were synthesized in methanolic media by reacting anhydrous FeCl3, H2bhsX and KOH in 1:2:4 mol ratio. The complexes were characterized using analytical, magnetic, spectroscopic and electrochemical techniques. In each complex the ligand binds the metal ion meridionally via the phenolate-O, imine-N and amide-O atoms. Room temperature solid state magnetic moments (5.75-6.09 μB) of the complexes are very similar and correspond to an S = 5/2 state. EPR spectra of the complexes reveal a subtle rhombic distortion of the FeIIIO4N2 sphere. Ligand-to-metal charge transfer bands are observed in the visible region (585 - 400 nm) of the electronic spectra. These bands shift to lower energy as the electron donating ability of the coordinated phenolate function increases. In cyclic voltammetry the complexes display an Fe(III) → Fe(II) reduction (-0.75 to -1.12 V) and irreversible oxidations (0.96-1.39 V). The redox potentials are significantly influenced by the electronic nature of the substituents. A linear correlation between the Fe(III)-Fe(II) reduction potentials and Hammett substituent constants is observed.