Synthesis and characterization of the crystal structure and magnetic properties of the hydroxyfluoride MnF2−x(OH)x (x ∼ 0.8)

Abstract

The new compound MnF_2−x(OH)_x (x ∼ 0.8) was synthesized by a hydrothermal route from a 1 : 1 molar ratio of lithium fluoride and manganese acetate in an excess of water. The crystal structure was determined using the combination of single crystal X-ray and neutron powder diffraction measurements. The magnetic properties of the title compound were characterized by magnetic susceptibility and low-temperature neutron powder diffraction measurements. MnF_2−x(OH)_x (x ∼ 0.8) crystallizes with orthorhombic symmetry, space group Pnn2 (no. 34), a = 4.7127(18), b = 5.203(2), c = 3.2439(13) Å, V = 79.54(5) ų and Z = 2. The crystal structure is a distorted rutile-type with [Mn(F,O)₄] infinite edge-sharing chains along the c-direction. The protons are located in the channels and form O–H⋯F bent hydrogen bonds. The magnetic susceptibility measurements indicate an antiferromagnetic ordering at ∼70 K and the neutron powder diffraction measurements at 3 K show that the ferromagnetic chains with spins parallel to the c-axis are antiferromagnetically coupled to each other, similarly to the magnetic structure of tetragonal rutile-type MnF₂ with isoelectronic Mn²⁺. MnF_2−x(OH)_x (x ∼ 0.8) is expected to be of great interest as a positive electrode for Li cells if the protons could be exchanged for lithium.