Microscopic Origin for Multistability in a Photomagnetic CoFe Prussian Blue Analogue

Switchable compounds attract growing interest, as they offer promising perspectives for high-density storage applications. Much effort has been invested in understanding the mechanisms involved in such properties, in order to prepare systems that are suitable for real applications. Compounds exhibiting an electronic transition that can be triggered by an external stimulus have been extensively studied. While most studies describe the switching properties of such systems in terms of a two-state model, the existence of multistability in switchable systems remains a controversial topic. In thispaper, we compare the thermally populated CoIIFeIII and photoinduced (CoIIFeIII)* states of the Na2Co4[Fe(CN)6](3) center dot 3 center dot 14H2O Prussian blue analogue. The comparison of the infrared spectroscopic data for the two CoIIFeIII and (CoIIFeIII)* states shows differences at a microscopic scale that cannot be explained in terms of a two-state model. These experimental data suggest a change in the coordination sphere of the sodium cation, which strongly supports a displacement of the sodium cation in the lattice between the two states. This direct evidence of several distinct CoFe states at an atomic level in this system highlights a new kind of multistability involving competitive metal-to-ligand interactions in a switchable compound.