Synthesis and Electrochemical Properties of Tetranuclear Di-μ-oxo-bis[di-μ-phenolatodiiron(III)] Complexes

Abstract

Abstract A series of tetrairon(III) complexes of di-μ-oxo-bis[di-μ-phenolatodiiron(III)] core, [{Fe2(L)(L′)}2(μ-O)2](PF6)2 (1–11), where L2− is the phenol-based macrocyclic compartmental ligand and (L′)− is acetate, monochloroacetate, dichloroacetate, trifluoroacetate, pentafluoropropionate, benzoate, p-nitrobenzoate, pentafluorobenzoate, diethyl phosphate, diphenyl phosphate, or diethyldithiophosphate for 1–11, respectively, were synthesized. X-ray crystallographic studies for 4, 7, and 9 indicated that two {Fe2(L)(L′)} units were connected by two oxo bridges to afford a tetranuclear di-μ-oxo-bis[di-μ-phenolatodiiron(III)] core. Cyclic voltammograms of 1–11 in acetonitrile showed a quasi-reversible or irreversible reduction wave between −332 and −620 mV (vs. Ag/Ag+), which were attributed to a two-electron process involving the Fe4III,III,III,III/Fe4II,II,III,III. The Fe4III,III,III,III/Fe4II,II,III,III potential shifted positive with a decrease in the electron-donating ability of the end-cap ligand, and a good linear correlation was found between the potentials and the pKa values of HL′. The Fe4II,II,III,III species were generated in acetonitrile by electrochemical reduction and showed broad intervalence transition bands in the range of 900–1500 nm.