Inorganic Chemistry, Vol.33, No.9, 1753-1755, 1994
Characterization of a Delocalized Mixed-Valence bis-Macrocyclic Diiron Compound
A mixed-valence Fe(II)/Fe(III) compound has been obtained by electrochemical oxidation of a bis-macrocyclic Fe(II)/Fe(II) complex. The binucleating ligand provides a delocalized pi system that facilitates electronic interaction between the metals. The Mossbauer spectrum of the mixed-valence compound consists of a single quadrupole-split doublet down to 4 K which establishes the equivalency of the two iron atoms. The cyclic voltammogram of the Fe(II)/Fe(II) species in rigorously dried acetonitrile shows two reversible oxidations with DELTAE1/2 = 500 mV. This corresponds to a comproportionation constant for the mixed-valence compound of 10(11). This large value also indicates the mixed-valence species is valence-averaged class III and is stabilized by delocalization. The mixed-valence compound has an intense near-infrared band (lambda(max) = 940 nm, epsilon = 27 000 M-1 cm-1). Analysis of this band using Hush’s equations for an intervalence transition also indicates the system is delocalized.