The immobilisation and reactivity of Fe(CN)63-/4- in an intrinsically microporous polyamine (PIM-EA-TB)

Protonation of the molecularly rigid polymer of intrinsic microporosity PIM-EA-TB can be coupled to immobilisation of Fe(CN)(6)(3-/4-) (as well as immobilisation of Prussian blue) into 1-2 nm diameter channels. The resulting films provide redox-active coatings on glassy carbon electrodes. Uptake, transport, and retention of Fe(CN)(6)(3-/4-) in the microporous polymer are strongly pH dependent requiring protonation of the PIM-EA-TB (pK(A) approximate to 4). Both Fe(CN)(6)(4-) and Fe(CN)(6)(3-) can be immobilised, but Fe(CN)(6)(4-) appears to bind tighter to the polymer backbone presumably via bridging protons. Loss of Fe(CN)(6)(3-/4-) by leaching into the aqueous solution phase becomes significant only at pH > 9 and is likely to be associated with hydroxide anions directly entering the microporous structure to combine with protons. This and the interaction of Fe(CN)(6)(3-/4-) and protons within the molecularly rigid PIM-EA-TB host are suggested to be responsible for retention and relatively slow leaching processes. Electrocatalysis with immobilised Fe(CN)(6)(3-/4-) is demonstrated for the oxidation of ascorbic acid.