Spectroscopic and Electrochemical Characterization of a Bis-Macrocyclic Diiron Compound

have been extensively investigated by optical and Mbssbauer spectroscopy as well as by electrochemistry.The binucleating ligand, TIED (tetraiminoethylene dimacrocycle), is an exceptionally good n acceptor as indicated by the Mossbauer spectrum, which shows a low value for the Center Shift and a high value for the Quadrupole SpUitting Parameter.This behavior is consistent with the unusually high value for the first oxidati0!1Also, extensive back-bonding from iron to an unoccupied n• orbital of the ligand may help produce the very short Fe-N (imine) distance 1.89 A that was found in the complex.Electrochemical oxidation apparently occurs at the metal centers, since the potential shows a large solvent dependence, which we attribute to axial ligand exchange by coordinating solvent molecules.Electrochemical reduction, while formally occurring at the ligand, shows indications of extensive mixing of ligand and metal orbitals.There is a change from two, well-separated one-electron reductions in CH 3 CN to closely overlapping reductions in DMF and H 2 0. Another indication of orbital mixing is the fact that substitution of Ni for Fe in the complex causes a large shift of 780 mV in the first ligand reduction potential.