A novel di-iron(III) structure based on an ageless ligand

Salen-type Schiff base ligands possess a N2O2 coordination site able to chelate transition metal ions. Reaction of such a ligand with FeCl3·6H2O leads to the formation of a genuine dinuclear L3Fe2 complex in which the ligand plays a double role. The structural determination confirms that each iron ion is wrapped up by a chelating tetradentate ligand while the third one ensures a bridge in between the two Fe ions and completes to six the metal coordination sphere. Such a bridge implies a non planar coordination of the chelating ligands and induces helicity around each metal ion. Crystals are true racemates made of homochiral Λ–Λ and Δ–Δ pairs. The magnetic study confirms the absence of a spin exchange interaction through the saturated diamino chain and the presence of an axial single ion zero field splitting (ZFS) D equal to −0.7 cm−1. The Mössbauer spectra show a unique asymmetric quadrupole-split doublet with isomer shift values, δ, of 0.342(2), 0.438(2) and 0.450(2) mm s−1, and quadrupole splittings, ΔEQ, of 0.826(4), 0.836(4) and 0.827(4) mm s−1 at 293, 80 and 4.5 K, respectively. These values are in agreement with a high-spin iron(III) site in a N3O3 ligand environment.

Two Schiff base ligands coordinate as chelating ligands while the third one acts as a chelating and bridging ligand, thus yielding an original true racemate high-spin dinuclear iron(III) complex (Λ–Λ and Δ–Δ pairs), as confirmed by magnetic, EPR and Mössbauer studies.Figure optionsDownload as PowerPoint slide