From Magnetic Chains to Sheets: The Impact of Hydrofluoric Acid Quantities in Mild Hydrothermal Synthesis on Mixed-Metal Fluoride Formation

Mixed-metal fluorides are excellent candidates for geometrically frustrated magnetic materials due to their extensive structural diversity and ability to host a plethora of low oxidation state transition metals with large magnetic moments. The utilization of the mild hydrothermal synthesis route to grow a series of mixed-metal fluorides with the general formula MIIM2IIIF8(H2O)2 (MII = Co, Mn, Ni, Cu, and Zn; MIII = Cr and V), as well as a rare earth containing fluoride, CoCe2F10(H2O)2, is discussed. All synthesized MIIM2IIIF8(H2O)2 fluorides were isostructural (orthorhombic, Fmmm) with the exception of CuV2F8(H2O)2, which crystallizes in the monoclinic (C2/c) crystal system due to Jahn–Teller distortions. CoCe2F10(H2O)2 crystallizes in orthorhombic space group Cmce. The extreme sensitivity of the hydrothermal reaction conditions on phase formation is discussed, in particular how the volume of HF used impacts the formation of specific compositions and structure types. In addition, the complex magnetic behavior of the MIIM2IIIF8(H2O)2 family is discussed.