Variable Dimensionality, Valence, and Magnetism in Fluoride-Rich Iron Phosphates BaxFex(PO4)F-y (1 <= x <= 3, 2 <= y <= 12)

Abstract

We report the synthesis and characterization of three fluoride-rich barium iron phosphates BaxFex(PO4)F-y (1 <= x <= 3, 2 <= y <= 12), which exhibited abundant structural chemistry, exhibiting diverse frameworks and connecting modes between [FeOnF6-n](m-) octahedra surrounding Fe2+ or Fe3+ ions. BaFe-(PO4)F-2 (I) consisted of two-dimensional [Fe(PO4)F-2](2-) sheets built from linear (infinity)[Fe2O6F4](10-) moieties formed by fluorine corner sharing FeO4F2 and FeO2F4 octahedra with linking PO4 tetrahedra. Mixed-valence Ba2Fe2(PO4)F-6 (II) possessed a three-dimensional framework containing Fe4O6F12 tetramers formed by the edge-sharing oxygen or fluorine atoms of cis-FeF4O2 octahedra. Ba3Fe3(PO4)F-12 (III) contained one-dimensional columns of (infinity)[Fe-3(PO4)F-12](6-) infinite sections built from cis-FeF4O2 and FeF5O octahedra and tetrahedral PO4 linkers. The magnetic characterization of BaxFex(PO4)F-y unveiled diverse magnetism: an S = 5/2 spin chain for (I), a weak ferrimagnet or canted antiferromagnet for (II) thanks to the presence of distinct Fe2+ and Fe3+ sites identified by Mossbauer spectroscopy, and coupled spin-trimers for (III).