From MagneticChains to Sheets: The Impact of HydrofluoricAcid Quantities in Mild Hydrothermal Synthesis on Mixed-Metal FluorideFormation

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 M^IIM₂^IIIF₈(H₂O)₂ (M^II = Co, Mn, Ni, Cu, and Zn; M^III = Cr and V), as well as a rare earth containing fluoride, CoCe₂F₁₀(H₂O)₂, is discussed. All synthesized M^IIM₂^IIIF₈(H₂O)₂ fluorides were isostructural (orthorhombic, <i>Fmmm)</i> with the exception of CuV₂F₈(H₂O)₂, which crystallizes in the monoclinic (<i>C</i>2/<i>c)</i> crystal system due to Jahn–Teller distortions. CoCe₂F₁₀(H₂O)₂ crystallizes in orthorhombic space group <i>Cmce</i>. 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 M^IIM₂^IIIF₈(H₂O)₂ family is discussed.