Synthesis and Characterization of the Crystal and Magnetic Structure and Properties of the Hydroxyfluorides Fe(OH)F and Co(OH)F

Abstract

The title compounds were synthesized by a hydrothermal route from a 1:1 molar ratio of lithium fluoride and transition metal acetate in an excess of water. The crystal structures were determined using a combination of powder and/or single crystal X-ray and neutron powder diffraction measurements. The magnetic structure and properties of Co(OH)F were characterized by magnetic susceptibility and low-temperature neutron powder diffraction measurements. M(OH)F (M = Fe, Co) crystallizes with structures related to diaspore-type-AlOOH, with the Pnma space group, Z = 4, a = 10.471 (3) Å, b = 3.2059 (10) Å, and c = 4.6977 (14) Å, and a = 10.2753(3) Å, b = 3.11813(7) Å, and c = 4.68437(14) Å, for Fe- and Co-phases, respectively. The structures consist of double chains of edge-sharing M(F,O)6 octahedra running along the b-axis. These infinite chains share corners and give rise to channels. The protons are located in the channels and form O-H…F bent hydrogen bonds. The magnetic susceptibility indicates an antiferromagnetic ordering at ~40 K and the neutron powder diffraction measurements at 3 K show that the ferromagnetic rutile-type chains with spins parallel to the short b-axis are antiferromagnetically coupled to each other, similarly to the magnetic structure of goethite -FeOOH.