Solution and solid state properties of Fe(III) complexes bearing N-ethyl-N-(2-aminoethyl)salicylaldiminate ligands

•Two new Fe(III) complexes synthesised.•Magnetic behaviour of newly synthesised Fe(III) complexes in the solid state.•Solution characterisation of six Fe(III) complexes (two new and four previously reported).•Magnetic behaviour in solution for all Fe(III) complexes.•Electrochemical studies by cyclic voltammetry.

The effect of the phenolate ring derivatisation on the magnetic properties of Fe(III) complexes bearing N-ethyl-N-(2-aminoethyl)salicylaldiminate ligands both in solid state and solution have been investigated. Two new complexes [Fe(3,5-Br-salEen)2]ClO4.EtOH (5) and [Fe(3,5-Br-salEen)2]BPh4.DMF (6) have been synthesised. SQUID magnetometry studies on these complexes showed that while complex 5 is in the low-spin (LS) state, complex 6 displays a gradual and incomplete spin crossover (SCO) transition over the temperature measured. Solution measurements on a series of six complexes – [Fe(salEen)2]ClO4 (1), [Fe(salEen)2]BPh4·0.5H2O (2), [Fe(5-Br-salEen)2]ClO4 (3), [Fe(5-Br-salEen)2]BPh4·DMF (4), [Fe(3,5-Br-salEen)2]ClO4·EtOH (5) and [Fe(3,5-Br-salEen)2]BPh4·DMF (6) – were performed by UV–vis and NMR spectroscopies and cyclic voltammetry. Solution studies show that the presence of electron withdrawing groups (bromine atoms) affect the electronic density at the phenolate ring, thus influencing the ligand field strength and the separation between the t2g and eg* energy levels. The presence of two bromide substituents at the phenolate ring has a more pronounced effect on the magnetic behaviour in solution than in the solid state, with both complexes 5 and 6 adopting preferentially the LS state. Electrochemical studies of complexes 1–6 reveal that the reduction of the metallic centres in the complexes with electron withdrawing groups is easier, with E1/2 values of iron moving to more positive potentials with the number of bromide substituents at the phenolate ring.

Graphical abstractSix Fe(III) complexes have been studied in solution by UV-vis spectroscopy, their magnetic susceptibility determined by the Evans' method and electrochemical properties investigated by cyclic voltammetry. Two newly reported complexes have also been studied in the solid state and their magnetic profiles determined by SQUID magnetometry and Mössbauer spectroscopy.Figure optionsDownload full-size imageDownload as PowerPoint slide