Spectroscopic and Electrochemical Characterization of a Bis-Macrocyclic Diiron Compound

• Published in: Inorganic chemistry 1994-04, Vol.33 (9), p.1748-1752
• Main Authors: Mountford, H. S, MacQueen, D. Brent, Li, Aiping, Otvos, John W, Calvin, Melvin, Frankel, Richard B, Spreer, Larry O
• Format: Article
• Language: English
• Subjects: 400400 > Electrochemistry; ABSORPTION SPECTROSCOPY; CHEMISTRY; COMPLEXES; Coordination compounds; ELECTROCHEMISTRY; ELECTRONIC STRUCTURE; Exact sciences and technology; Inorganic chemistry and origins of life; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; IRON COMPLEXES; MOESSBAUER EFFECT; Preparations and properties; SPECTROSCOPY; TRANSITION ELEMENT COMPLEXES 400201 > Chemical & Physicochemical Properties
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic00087a005

The properties of the complex [Fe[sub 2](C[sub 20]H[sub 36]N[sub 8])(CH[sub 3]CN)[sub 4]](ClO[sub 4])[sub 4] have been extensively investigated by optical and Moessbauer spectroscopy as well as by electrochemistry. The binucleating ligand TIED (tetraiminoethylene dimacrocycle) is an exceptionally good [pi] acceptor as indicated by the Moessbauer spectrum, which shows a low value for the center shift and a high value for the quadrupole splitting parameter. This behavior is consistent with the unusually high value for the first oxidation potential (1.18 V vs NHE) since Fe[sup 2+] is a much better [pi] donor than Fe[sup 3+]. Also, extensive back-bonding from iron to an unoccupied [pi]* orbital of the ligand may help produce the very short Fe-N(imine) distance of 1.89 [angstrom] that was found in the complex. Electrochemical oxidation apparently occurs at the metal centers, since the potential shows a large solvent dependence, which is attributed 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[sub 3]CN to closely overlapping reductions in DMF and H[sub 2]O. 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.