Stereochemistry and spin configuration of NN′-bis(2-pyridylmethyl)-ethyleneddiamine complexes of iron(III) in the solid state and in aqueous solution

Abstract

High-spin [Fe(pmen)Cl₂]Cl and low-spin [Fe(pmen)(OH₂)(OH)][ClO₄]₂ complexes (pmen is the title ligand) have been prepared and characterized by spectroscopic and magnetic measurements. Electronic and e.p.r. spectra suggest that the complexes have a cis-type geometry both in the solid state and in aqueous solution. Peculiar features observed in solution are aquation of the cation of the chloride salt which effects electron pairing, whilst a change from low to high spin, accompanied by a structural rearrangement, occurs when the interaction of the complexes in aqueous solution with an optically active polyelectrolyte (Which does not absorb over the wave-length region explored), make possible an assignment of cis-α geometry to the high-spin form and cis-β geometry to the low-spin species, in agreement with predictions from qualitative steric considerations. Implications of stereochemical demands of the complexes on variation of the spin configuration of the iron are also discussed.