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

Cationic iron(III) complexes of the type [FeLn(H2O)(2)]NO3 (n = 1 or 2) were accessed from the interaction of Fe(NO3)(3)center dot 9H(2)O with [N2O2] 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, [(FeLX2)-X-n]NO3. The compounds were characterized by elemental analyses, FT-IR, UV-Vis, solution electrical conductivity, FAB mass, H-1 and C-13 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 (Delta E-p > 100 mV) assignable to Fe(III)/Fe(II) couple with negative half wave potential. The ground state geometries of the aquo complex, [FeL2(H2O)(2)]NO3 and pyridine complex, [FeL2(Py)(2)]NO3 were ascertained by density functional theory using DMOL3 program with BLYP functional. (C) 2012 Elsevier B. V. All rights reserved.