Synthesis and characterisation of the quaternary nitride-fluoride Ce2MnN3F2−δ

Abstract

Ce₂MnN₃F_2−δ has been synthesised via low-temperature fluorination of the ternary nitride Ce₂MnN₃. To the best of our knowledge, Ce₂MnN₃F_2−δ is the first quaternary nitride-fluoride to be reported. The reaction of Ce₂MnN₃ with 10% F₂/N₂ at 95–115 °C yields the fluorinated phase Ce₂MnN₃F_2−δ, with tetragonal symmetry (P4/nmm a = 3.8554(4) Å and c = 13.088(4) Å based on neutron powder diffraction), accompanied by starting material. Rietveld refinement supports a staged fluorine insertion reaction (into alternate rocksalt layers) to give a product with stoichiometry Ce₂MnN₃F_2−δ. A comparison with the formation of Sr₂TiO₃F₂ and the isostructural LaSrMnO₄F indicates that two F⁻ anions are inserted but no F⁻/N³⁻ substitution takes place. Magnetic susceptibility measurements show a transition from Pauli paramagnetic behaviour, in Ce₂MnN₃, to paramagnetic behaviour upon fluorination. The effective magnetic moment in Ce₂MnN₃F_2−δ, μ_eff = 5.38 μ_B, is consistent with an intermediate value between that of Mn³⁺ (4.9 μ_B) and Mn²⁺ (5.9 μ_B) supporting the proposed stoichiometry, Ce₂MnN₃F_2−δ.