The immobilisation and reactivity of Fe(CN)₆ ^3−/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 ≈ 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. [Figure not available: see fulltext.].