Syntheses and Characterization of the Mixed-Valent Manganese(II/III) Fluorides Mn2F5 and Mn3F8

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We obtained single crystals of the binary mixed-valent fluorides Mn 2 F 5 and Mn 3 F 8 using a high-pressure/high-temperature approach. Mn 2 F 5 crystallizes isotypic to CaCrF 5 in the monoclinic space group C 2/ c (No. 15), with a = 8.7078(8) Å, b = 6.1473(6) Å, c = 7.7817(7) Å, β = 117.41(1)°, V = 369.80(6) Å 3, Z = 4, and mC 28 at T = 173 K. Mn 3 F 8 crystallizes in the monoclinic space group P 2 1 (No. 4) with a = 5.5253(2) Å, b = 4.8786(2) Å, c = 9.9124(4) Å, β = 92.608(2)°, V = 266.92(2) Å 3, Z = 2, and mP 22 at T = 183 K and presents a new structure type. Crystal-chemical reasoning, CHARDI calculations, and quantum-chemical calculations allowed for the assignment of the oxidation states of the Mn atoms. In both bulk compounds, MnF 2 was present as an impurity, as evidenced by powder X-ray diffraction and IR and Raman spectroscopy.