Cyanide-Bridged Iron(II,III) Cube with Multistepped Redox Behavior

A building unit of Prussian blue was isolated as a cyanide-bridged iron cube of [FeII4FeIII4(CN)12(tp)8]·12DMF·2Et2O·4H2O [tp− = hydrotris(pyrazolyl)borate]. A cyclic voltammogram showed quasi-reversible four-stepped redox waves, which correspond to [FeIII4FeII4]/[FeIII5FeII3]+, [FeIII5FeII3]+/[FeIII6FeII2]2+, [FeIII6FeII2]2+/[FeIII7FeII1]3+, and [FeIII7FeII1]3+/[FeIII8]4+ processes. Controlled potential absorption spectral measurements revealed two intervalence charge-transfer bands at 816 and 1000 nm, which were assigned to charge transfers from FeII ions to adjacent and remote FeIII ions, respectively, in the cube.