Anion influence on spin state in two novel Fe(III) compounds: [Fe(5F-sal2333)]X

Structural and magnetic data on two iron (III) complexes with a hexadentate Schiff base chelating ligand and Cl¯ or BPh₄¯ counterions are reported. In the solid state, the Cl¯ complex [Fe(5F-sal₂333)]Cl, 1, is high spin between 5–300 K while the BPh₄¯ analogue [Fe(5F-sal₂333)]BPh₄, 2, is low spin between 5–250 K, with onset of a gradual and incomplete spin crossover on warming to room temperature. Structural investigation reveals different orientations of the hydrogen atoms on the secondary amine donors in the two salts of the [Fe(5F-sal₂333)]⁺ cation: high spin complex [Fe(5F-sal₂333)]Cl, 1, crystallizes with non-meso orientations while the spin crossover complex [Fe(5F-sal₂333)]BPh₄, 2, crystallizes with a combination of meso and non-meso orientations disordered over one crystallographic site. Variable temperature electronic absorption spectroscopy of methanolic solutions of 1 and 2 suggests that both are capable of spin state switching in the solution.