Safer Synthesis Of Fluorophosphate Crystals

A straightforward route to preparing transition-metal fluorophosphate crystals has been described by researchers at the University of Southampton, in England, opening a new family of complexes to potential applications in energy storage, magnetic, and catalytic materials (J. Am. Chem. Soc., DOI: 10.1021/ja201096b). Metal oxide frameworks have long been popular for such uses. Replacing the oxide with fluoride is one way to alter the materials’ chemistry, dimensions, and performance. Jennifer A. Armstrong, Edward R. Williams, and Mark T. Weller combined anhydrous transition-metal fluorides with phosphoric acid and a fluoride salt or structure-directing agent, heated the mixture in a hydrothermal bomb, and allowed the products to crystallize. The approach eliminates the need for hydrofluoric acid, making synthesis easier and safer, the authors say. So far, they’ve prepared 45 Mn(III), Fe(III), Co(II), and Cu(II) complexes and characterized some of them in ion-exchange reactions, in lithium-insertion reactions of interest for rechargeable batteries, and in magnetic-susceptibility tests. The group observed that the fluoride ions often bridge metal sites, and the frameworks have fluoride-lined channels that aid cation mobility.