Solvatomorphism and anion effects in predominantly low spin iron(iii) Schiff base complexes

Abstract

A series of iron(III) complexes [Fe(naphEen)₂]X·sol (naphEen = 1-{[2-(ethylamino)-ethylimino]methyl}-2-naphtholate; X = F, sol = 0.5CH₂Cl₂·H₂O 1; sol = H₂O, X = Cl, 2 and X = Br 3) and [Fe(naphEen)₂]I 4 has been prepared. The UV-Vis spectra reveal clear differences for 1 which DFT/TDDFT calculations suggest are due to an equilibrium between [Fe(naphEen)₂]F and [Fe(naphEen)₂F], the latter having a coordinated F ligand. The X-ray crystal structures of 2–4 show LS Fe(III) centres in all cases and extensive aryl interactions that link the Fe centres into supramolecular squares. In 3 at room temperature the compound loses half an equivalent of water resulting in a change in space group from Monoclinic P2₁/n to C2/c. Magnetic studies indicate that 1 is trapped in a mixed spin state being ca. 40% HS while 2–4 are effectively low spin up to 350 K. In contrast, Mössbauer spectroscopic studies of 1 indicate a gradual but incomplete spin crossover. The magnetic properties of 2–4 contrast with the related [Fe(salEen-X)₂]anion derivatives which are often spin crossover active.