UV–vis spectral changes for the reaction of 3 (0.99 mM) with IBX-ester at −35 °C in CH3CN (left). Freeze-quench Mössbauer spectrum for 3 (5 mM) + IBX-ester at −5 °C in CH3CN/2-methylbutane after 22 s (right). The species are ls-FeII
3, thick solid black; hs-FeII
3, dashed black; FeII intermediate, blue; FeIVO intermediate, red; sum of fitted species, thin black line; Fe(III) products, unfitted.