Strong magnetic exchange and frustrated ferrimagnetic order in a weberite-type inorganic-organic hybrid fluoride.

We combine powder neutron diffraction, magnetometry and Fe Mössbauer spectrometry to determine the nuclear and magnetic structures of a strongly interacting weberite-type inorganic-organic hybrid fluoride, FeF(H taz). In this structure, Fe and Fe cations form magnetically frustrated hexagonal tungsten bronze layers of corner-sharing octahedra. Our powder neutron diffraction data reveal that, unlike its purely inorganic fluoride weberite counterparts which adopt a centrosymmetric Imma structure, the room-temperature nuclear structure of FeF(H taz) is best described by a non-centrosymmetric Ima2 model with refined lattice parameters a = 9.1467(2) Å, b = 9.4641(2) Å and c = 7.4829(2) Å. Magnetic susceptibility and magnetization measurements reveal that strong antiferromagnetic exchange interactions prevail in FeF(H taz) leading to a magnetic ordering transition at T = 93 K. Analysis of low-temperature powder neutron diffraction data indicates that below T, the Fe sublattice is ferromagnetic, with a moment of 4.1(1) µ per Fe at 2 K, but that an antiferromagnetic component of 0.6(3) µ cants the main ferromagnetic component of Fe, which aligns antiferromagnetically to the Fe sublattice. The zero-field and in-field Mössbauer spectra give clear evidence of an excess of high-spin Fe species within the structure and a non-collinear magnetic structure. This article is part of the theme issue 'Mineralomimesis: natural and synthetic frameworks in science and technology'.