On new hydrated fluorides of trivalent manganese

Abstract Three new hydrated fluorides of Mn 3+ have been obtained from Ni 2+ (or Cu 2+ ) and Mn 3+ solutions in 40% hydrofluoric acid: NiMnF 5 · 7H 2 O, CuMnF 5 · 7H 2 O, and Cu 3 Mn 2 F 12 · 12H 2 O. The monoclinic symmetries and the lattice constants of the two heptahydrates have been established. The crystal structure of Cu 3 Mn 2 F 12 · 12H 2 O has been refined using single-crystal X-ray diffraction data: it is triclinic with space group P 1 and parameters a = 7.568(1)A, b = 7.558(1)A, c = 8.168(1)A, α = 91.32°, β = 89.72°, γ = 92.61°, Z = 1; R = 0.046 for 4040 independent reflections. It is isostructural with the homologous V, Cr, and Fe compounds. It can be considered as an inverse perovskite with formulation [MnF 6 ][MnF 6 2 ][Cu(H 2 O) 4 F 2 2 ] 3 . Whereas the two heptahydrates are paramagnetic down to 2 K, a spontaneous magnetization occurs below T c = 3.8 ± 0.2 K for Cu 3 Mn 2 F 12 · 12H 2 O. Hypotheses have been proposed to account for the field dependence of the magnetization by taking into account the superexchange mechanisms between two Jahn-Teller ions.