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 BPh3 and +350 mV for B(C6F5)3. Electron transfer from [Fe(CN-B(C6F5)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.