Molecule-based magnets with TC above room temperature: Improved synthesis of vanadium–chromium Prussian blue analogues with inserted alkali cations

We report the synthesis of several new vanadium–chromium Prussian blue analogues with a Curie temperature above room temperature. A catalytic amount of vanadium(III) during the synthesis allows to get improved magnetic properties, stable Curie temperatures (TC) and a magnetisation at saturation in satisfying agreement with the stoichiometry. The insertion of alkali cations (potassium, rubidium, caesium) allows to reach a V:Cr stoichiometry close to 6:5, hence to enhance the number of magnetic neighbours compared to the usual V:Cr 3:2 stoichiometry and to increase accordingly the Curie temperature. For the same stoichiometry, the ferrimagnetic ordering temperature varies slightly with the nature of the inserted alkali cation (TC/K = 360, 346 and 340 K for the potassium, rubidium and caesium derivatives, respectively). X-ray absorption spectroscopy allows to characterise the local surroundings of the chromium and vanadium ions and to propose an explanation of the magnetic properties.

Graphical abstractWhen vanadium–chromium Prussian blue analogues are synthesized in presence of catalytic amount of vanadium(III) and excess of alkali cations, one gets stable Curie temperatures (TC) well above room temperature and magnetisation in agreement with stoichiometry. X-ray absorption spectroscopy at the chromium and vanadium edges allows to discuss the magnetic properties.Figure optionsDownload full-size imageDownload as PowerPoint slide