Synthesis and Magnetic Properties of the Ternary Oxofluoride Fe 3 Sb 4 O 6 F 6

The new compound Fe 3 Sb 4 O 6 F 6 was prepared by hydrothermal synthesis and its crystal structure was determined from single‐crystal X‐ray diffraction data. The synthesis was made under slightly basic conditions to prevent oxidation of Fe 2+ to Fe 3+ . The compound crystallizes in the cubic space group I ‐43 m with separate crystallographic sites for Fe 2+ and Sb 3+ . Fe 3 Sb 4 O 6 F 6 is isostructural with M 3 Sb 4 O 6 F 6 (M = Co, Ni, Zn). The crystal structure is comprising distorted [FeO 2 F 4 ] octahedra connected via corner sharing at F‐atoms and [SbO 3 ] trigonal pyramids that form [Sb 4 O 6 ] units that connect via O‐atoms to the Fe‐atoms. Mössbauer spectroscopy measurements on the hydrothermal synthesis products prove the majority phase contains Fe in the oxidation state +2. Powder X‐ray diffraction suggests that an additional phase of the Mössbauer sample containing Fe 3+ can be attributed to FeSbO 2 F 2 as secondary phase. Fe 3 Sb 4 O 6 F 6 exhibits antiferromagnetic order below ca. 72 K succeeded by a second magnetic phase transition at ca. 30 K. Strong antiferromagnetic spin‐exchange interaction is attributed to 180° Fe–F–Fe superexchange pathways identified in the crystal structure.