Revisiting the TCNQF Catalysis Mechanism for the [Fe(CN) ] -S O /S O Redox Reaction.

Published data suggest that sparingly soluble metal complexes of , where n=0, 1, 2, 4, can act as heterogeneous catalysts for the kinetically very slow - / reaction in aqueous solution. This study shows that the coordination polymer , participates as a homogeneous catalyst via an extremely small concentration of dissolved . This finding suggests that the generally accepted mechanism of catalysis by based solids needs to be revisited to ascertain the role of homogeneous pathways. In the present study, UV-visible spectrophotometry was used to examine the catalysis of the aqueous redox reaction of (1.0 mM) with (100 mM) in the presence of (i) a precursor catalyst, ; (ii) the catalyst, , as the water soluble Li salt; and (iii) . A homogeneous reaction scheme that utilises the couple is provided. In the case of derived from highly soluble , quantitative conversion of 1.0 mM to 0.50 mM occurs with complete reduction of to being rapidly accelerated by sub-micomolar concentrations of . generated in the catalytic cycle, reacts with to reform and produce . Along with the rapid catalytic reaction, the sluggish competing reaction between and occurs to give , which is protonated to , along with a trace amount of . On addition of the precursor catalyst, , rapid reduction with occurs to form - the active catalyst. added to water is shown to be sufficiently soluble to provide adequate to act as the catalyst for the - / reaction.