Magnetic and Optical Bistability Driven by Thermally and Photoinduced Intramolecular Electron Transfer in a Molecular Cobalt−Iron Prussian Blue Analogue

A soluble molecular analogue of photoresponsive Co/Fe Prussian blues is described within this report. As judged via a variety of spectroscopic, magnetic, and crystallographic methods, electron transfer within the octanuclear complex (below 250 K) converts paramagnetic red crystals into green diamagnetic ones. The color and magnetic changes are associated with the transformation of Fe<sup>III</sup><sub>LS</sub>-CN-Co<sup>II</sup><sub>HS</sub> units into Fe<sup>II</sup><sub>LS</sub>-CN-Co<sup>III</sup><sub>LS</sub> fragments in manner that is identical to that found for the A<i><sub>n</sub></i>[Co(OH<sub>2</sub>)<sub>(6-6</sub><i><sub>m</sub></i><sub>)</sub>][Fe(CN)<sub>6</sub>]<i><sub>m</sub></i>·<i>x</i>H<sub>2</sub>O (A<i><sub>n</sub></i> = alkali metal cation) family of three-dimensional Prussian blues. Moreover, this intramolecular electron transfer can be quantitatively circumvented via rapid thermal quenching and reversed via simple white light irradiation at low temperatures. Remarkably the data suggests that thermally or photoinduced paramagnetic metastable phases are identical and exhibit long relaxation times that approach 10 years at 120 K.