A Peculiar Photo-Induced Transformation Exalted in Nanometric Size CoFe Prussian Blue Analogs

The discovery of a photomagnetic effect in a CoFe Prussian blue analog (PBA) has triggered a growing interest for photo-switchable bimetallic cyanide-bridged systems. Nevertheless, in between cyanide-bridged extended coordination polymers and discrete molecules, the photo-switching phenomena are much less well known in nano-sized materials. A photo-induced transformation, specific to the nanometric size, is evidenced by magnetometry and by X-ray absorption spectroscopy at the Co and Fe K-edges in an alkali cation free Prussian blue analog. The nanoparticles before irradiation can be described as having a core-shell structure, the core being made of the well-known fcc-Co-II(HS)Fe-III structure of CoFe PBAs while the shell contains Co-II ions in octahedral geometry and significantly distorted Fe(CN)(6) entities. Irradiation induces a change of the local structures around the transition metal ions, which remain in the same oxidation state, with different behaviors of the Co and Fe sub-lattices.