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 [(Fe4Fe4III)-Fe-II(CN)(12)(tP)(8)]center dot 12DMF center dot 2Et(2)O center dot 4H(2)O [tp(-) = hydrosis(pyrazolyl)borate]. A cyclic voltammogram showed quasi-reversible four-stepped redox waves, which correspond to [(Fe4Fe4II)-Fe-III]/ [(Fe5Fe3II)-Fe-III](+), [(Fe5Fe3II)-Fe-III](+)/[(Fe6F2II)-F-III](2+), [(Fe6Fe2II)-Fe-III](2+)/[(Fe7Fe1II)-Fe-III](3+), and [(Fe7Fe1II)-Fe-III](3+)/[Fe-8(III)](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 Fe-II ions to adjacent and remote Fe-III ions, respectively, in the cube.