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

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 (NPD) measurements. The magnetic
structure and properties of Co­(OH)F were characterized by magnetic
susceptibility and low-temperature NPD measurements. M­(OH)F (M = Fe
and Co) crystallizes with structures related to diaspore-type α-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 the iron and cobalt 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 NPD 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 α-FeOOH.