Reactivity of tris(acetylacetonato) iron(III) with tridentate [ONO] donor Schiff base as an access to newer mixed-ligand iron(III) complexes

Two new mixed-ligand iron(III) complexes, [Fe(Ln)(acac)(C2H5OH)] incorporating coordinated ethanol from the reaction solvent were accessed from the reaction of [Fe(acac)3] with [ONO] donor dibasic tridentate unsymmetrical Schiff base ligands derived from condensation of 2-hydroxy-1-napthaldehyde with 2-aminophenol (H2L1) or 2-aminobenzoic acid (H2L2). The thermal study (TGA–DTA) provided evidence for weakly bound ethanol which is readily substituted by neutral N-donor molecule imidazole, benzimidazole or pyridine to produce an array of newer complexes, [Fe(Ln)(acac)X] (n = 1, 2; X = Im, Bim, Py). The compounds were characterized by elemental analyses, FT-IR, UV–vis, solution electrical conductivity, FAB mass, 1H and 13C NMR spectroscopy. Room temperature magnetic susceptibility measurements (μeff ∼ 5.8 B.M.) are consistent with spin-free octahedral iron(III) complexes. Cyclic voltammetry of ethanol complexes revealed a quasi-reversible one electron redox response (ΔEp > 100 mV) for the Fe(III)/Fe(II) couple. Low half wave redox potential (E1/2) values suggested easy redox susceptibility. The ground state geometries of the ethanol and imidazole complexes have been ascertained to be distorted octahedral by density functional theory using DMol3 program at BLYP/DNP level.

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► Mixed-ligand Schiff base complexes of the type [Fe(Ln)(acac)(EtOH)] have been synthesized from the reaction of tris(acetylacetonato) iron(III) and tridentate Schiff bases.
► Reaction of the complexes with neutral donor molecules led to substitution of labile ethanol molecule at the axial coordination site yielding newer mixed-ligand complexes.
► All the complexes are high spin and non-electrolytic in nature.
► Quantum chemical DFT study revealed six-coordinate distorted octahedral structure of the complexes with small HOMO–LUMO energy gap.