Tuning the formal potential of ferrocyanide over a 2.1 V range

We report the synthesis and characterization of homoleptic borane adducts of hexacyanoferrate(ii). Borane coordination blueshifts d–d transitions and CN IR and Raman frequencies. Control over redox properties is established with respect to borane Lewis acidity, reflected in peak anodic potential shifts per borane of +250 mV for BPh(3) and +350 mV for B(C(6)F(5))(3). Electron transfer from [Fe(CN-B(C(6)F(5))(3))(6)](4–) to photogenerated [Ru(2,2′-bipyridine)(3)](3+) is very rapid, consistent with voltammetry data. Coordination by Lewis acids provides an avenue for selective modification of the electronic structures and electrochemical properties of cyanometalates.