Reversible single crystal photochemistry and spin state switching in a metal-cyanide complex.

Magott, Michał; Arczyński, Mirosław; Malec, Leszek; Rams, Michał; Rouzières, Mathieu; Rogalev, Andrei; Wilhelm, Fabrice; Oyarzabal, Itziar et al. · Nat Commun · 2025

basic_science · Level V

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Abstract

Manipulating the physical properties of solid matter using only photons is a major challenge in materials science. However, achieving such control over a chemical reaction in the solid state is even more challenging. Here we demonstrate the reversible photochemistry occurring in a single crystal of a simple cyanide complex, K<sub>4</sub>[Mo<sup>III</sup>(CN)<sub>7</sub>]·2H<sub>2</sub>O. Upon exposure to visible light at different wavelengths, a reversible breaking and reformation of dative bonds is triggered, resulting in a photoswitching of the Mo<sup>III</sup> coordination geometry between 6- and 7-coordinate. This transformation, in turn, induces a spin state change. The observed solid-state photochemical reactivity is robust, quantitative and occurs at a record-high temperature. It paves the way for the development of new photo-switchable high-temperature magnets and nanomagnets.