CHARACTERIZATION OF A DELOCALIZED MIXED-VALENCE BIS-MACROCYCLIC DIIRON COMPOUND

A mixed-valence Fe(II)/Fe(III) compound has been obtained by electroch emical oxidation of a bis-macrocyclic Fe(II)/Fe(II) complex. The binuc leating ligand provides a delocalized pi system that facilitates elect ronic interaction between the metals. The Mossbauer spectrum of the mi xed-valence compound consists of a single quadrupole-split doublet dow n 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 a cetonitrile shows two reversible oxidations with DELTAE1/2 = 500 mV. T his 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 delocaliza tion. The mixed-valence compound has an intense near-infrared band (la mbda(max) = 940 nm, epsilon = 27 000 M-1 cm-1). Analysis of this band using Hush's equations for an intervalence transition also indicates t he system is delocalized.