Spin crossover behaviour of asymmetrical iron(iii) Schiff base complexes from ethylenediamine†

Abstract

Novel asymmetrical Fe(III) Schiff base coordination complexes, with the N₄O₂ coordination environment, exhibiting abrupt spin crossover (SCO) behaviour with a wide hysteresis loop of 27 K, have been synthesised from an ethylenediamine based asymmetrical Schiff base ligand viz. N-(2-aminoethyl)salicylaldimine (saen) and characterised via single crystal XRD measurements, variable temperature magnetic studies and Mössbauer measurements. The single crystal XRD measurements prove that the compound is a mixture of two fractions, one with methanol and the other without methanol, viz, [Fe(saen)₂]NO₃·CH₃OH at 299 K (1–299) and at 173 K (1–173) and [Fe(saen)₂]NO₃ at 173 K (2–173), confirming that the Fe(III) centre has a distorted octahedral coordination geometry having two deprotonated asymmetrical tridentate saen ligands, counterbalanced by a nitrate anion and methanol solvent molecule in 1 while 2 has a non-solvate form. An extended hydrogen bonding network between the amino hydrogen atoms of the saen ligand, nitrate counteranion, and methanol solvate molecule is observed in fraction 1, while an extended zig-zag hydrogen bonding between the nitrate anion and amino hydrogens of saen is observed in fraction 2. Furthermore, the complex has been characterised by variable temperature magnetic susceptibility measurements and ⁵⁷Fe Mössbauer spectroscopy, confirming the SCO nature.