Synthesis, reactivity, thermal, electrochemical and magnetic studies on iron(III) complexes of tetradentate Schiff base ligands

摘要

Cationic iron(III) complexes of the type [FeL~n(H _2O) _2]NO _3 (n = 1 or 2) were accessed from the interaction of Fe(NO _3) _3·9H _2O with [N _2O _2] donor Schiff base (L) in 1:1 molar ratio. The Schiff base ligands were prepared from condensation of 2-hydroxy-1- naphthaldehyde with o-phenylenediamine or ethylenediamine in 2:1 molar ratio. Reaction of the aquated complexes with neutral N-donor molecules (X) viz. imidazole, benzimidazole and pyridine led to substitution of weakly held axial aquo groups affording new mixed ligand complexes, [FeL nX _2]NO _3. The compounds were characterized by elemental analyses, FT-IR, UV-Vis, solution electrical conductivity, FAB mass, ~1H and ~(13)C NMR (ligands only) spectroscopy. The thermal study provided unambiguous evidence for the occurrence of coordinated water in the complexes. Room temperature magnetic susceptibility measurements are consistent with high spin octahedral iron(III) complexes. Cyclic voltammetry revealed a quasi-reversible one electron redox response (ΔE _p > 100 mV) assignable to Fe(III)/Fe(II) couple with negative half wave potential. The ground state geometries of the aquo complex, [FeL ~2(H _2O) _2]NO _3 and pyridine complex, [FeL ~2(Py) _2]NO _3 were ascertained by density functional theory using dmol3 program with BLYP functional.