Pentacoordinated Chloro-Iron(III) Complexes with Unsymmetrically Substituted N2O2 Quadridentate Schiff-Base Ligands: Syntheses, Structures, Magnetic and Redox Properties

Abstract

Abstract:Since their development in the 1930s, Schiff-base complexes have played an important role in the field of coordination chemistry. Here, we report the synthetic, spectral, structural, magnetic and electrochemical studies of two new pentacoordinated neutral chloro-iron(III) complexes (3,5) supported by dianionic [N 2 O 2 ] 2− tetradentate Schiff-base ligands unsymmetrically substituted by either a pair of acceptor (F and NO 2 ) or donor (ferrocenyl and OCH 3 ) groups. The electron-withdrawing Schiff-base proligand 2 and the complexes 3 and 5 were prepared in good yields (79-86%). Complex 3 was readily obtained upon reaction of 2 with anhydrous iron chloride under basic conditions, while the bimetallic derivative 5 was synthesized by condensation of the free amino group of the ferrocenyl-containing O,N,N-tridentate half-unit 4 with 5-methoxysalicylaldehyde in the presence of FeCl 3 . The three new compounds were characterized by elemental analysis, FT-IR, UV-Vis, mass spectrometry and in the case of 2 by multinuclear NMR spectroscopy. The crystal structures of 3 and 5 revealed that in the two five-coordinate monomers, the iron atom showed distorted square-pyramidal geometry, with the N and O atoms of the Schiff-base ligand occupying the basal sites and the chlorine atom at the apex of the pyramid. Magnetic measurements showed a high-spin configuration (S = 5/2) for the Fe(III) ion in 3 and 5. Reduction associated with the Fe(III)/Fe(II) redox couple occurred at −0.464 and −0.764 V vs. Ag/Ag + , and oxidation taking place at the Schiff-base ligand was observed at 1.300 and 0.942 V vs. Ag/Ag + for 3 and 5, respectively. A high-electronic delocalization of the Schiff-base ligand substituted by fluoro and nitro groups stabilizes the Fe(II) oxidation state and shifts the redox potential anodically.

Homoleptic CoII, NiII, CuII, and ZnII Complexes Based on 8‐Hydroxylquinoline Schiff Base Derivative: a Combined Synthetic, Spectral, Structural, and Magnetic Study

“…Proligand H 2 L Adopts an E‐conformation, with respect to the C=N double bond. The azomethine C=N bond length (1.295(7) Å) is similar to those previously measured for structurally related Ar–C(H)=N–Ar Schiff base compounds . The metric parameters observed in the aromatic cycles reveal a strong delocalization throughout the π‐system, with average C–C bond lengths of 1.382 Å, 1.395 Å, and 1.398 Å, for the o ‐phenylene, fused C 6 and pyridine rings, respectively.…”

Synthesis, characterization, and investigation of some properties of the new symmetrical bisimine Ni(II), Zn(II), and Fe(III) complexes derived from the monoimine ligand

“…So the coordination geometry around the Fe(III) ions can be described as slightly distorted square pyramidal geometry, τ = 0.018 (ideally τ = 0). [ 29,40–42 ] There are no hydrogen bonds or significant intermolecular interactions in the crystal structure of [FeLCl]. Details of data collection and crystal structure determinations are given in Table 1.…”

“…Salen‐type complexes have been used as electrocatalysts. [ 27–30 ] Electrochemical studies provide valuable information regarding catalytic processes. Electrochemical properties of ligands and complexes were investigated by cyclic voltammetry (CV) to determine possible technological applications.…”

Pentacoordinated isothiocyanate iron(III) complexes supported by asymmetric tetradentate donor and acceptor Schiff base ligands: Spectral, Structural and Hirshfeld Surface Analyses

“…Reagents were purchased from commercial suppliers and used without further purification. The chloroiron(III) precursors 1 and 2 were synthesized according to the published procedure [55]. Solidstate FT-IR spectra were recorded on a Perkin-Elmer Model 1600 FT-IR spectrophotometer with KBr disks in the 4000 to 450 cm -1 range.…”

“…Herein we report on the synthesis and full characterization of two new neutral pentacoordinate iron(III) complexes featuring unsymmetric tetradentate Schiff base ligands substituted by either a pair of acceptor (L A : 4-fluorophenyl/nitro) or donor (L D : ferrocenyl [54]/methoxy) groups, with terminal N-coordinated isothiocyanato co-ligand. Both mixed-ligand complexes of the type [Fe(L A /L D )(NCS)] 3 and 4, respectively, were prepared starting from their previously reported corresponding pentacoordinated chloro iron(III) precursors 1 and 2 [55], upon reaction with sodium thiocyanate (see formulas in Scheme 1). Complex 3 was structurally characterized.…”