Solvation and reactivity of a helical binuclear iron(II) complex with a tetradentate Schiff-base ligand

Reaction of 2-acetylpyridine, hydrazine, and an iron(II) salt gives a low-spin binuclear iron(II) complex, Fe₂(pmk)₃]⁴⁺, in which three tetradentate Schiff base ligands span the two metal centres to give a complex of helical geometry. We report solubilities of the iodide and perchlorate salts, in H₂O, in aqueous MeOH, and in aqueous DMSO (perchlorate only), up to 60% by vol of organic cosolvent. Transfer chemical potentials for the complex cation from H₂O into the respective mixed solvents have been derived from these solubilities, to give a picture of solvation of this complex in the media studied. Kinetics of base hydrolysis of Fe₂(pmk)₃]⁴⁺ have been established, in H₂O and in 40% MeOH, 20 and 40% i -PrOH, and 20 and 40% DMSO, at 298.2 K. The reactivity of Fe₂(pmk)₃]⁴⁺ is discussed in relation to reactivities of a selection of iron(II)-diimine complexes, ranging from Fe(bipy)₃]²⁺ and Fe(phen)₃]²⁺ to ligand-encapsulated cage complexes.