Materialization of a geometrically frustrated magnet in a hybrid coordination framework: a study of the iron(II) oxalate fluoride framework, KFe(C₂O₄)F

Here we discuss magnetic hybrid coordination frameworks in relation to the realization of new geometrically frustrated magnets. In particular, we present the nuclear and magnetic structures of one such system—the Fe²⁺-based oxalate fluoride framework KFe(C₂O₄)F—through analysis of the powder neutron diffraction and muon spectroscopy data. KFe(C₂O₄)F retains an orthorhombic Cmc2₁ structure upon cooling to 2 K composed of quasi-one-dimensional iron fluoride chains connected to a distorted triangular network via oxalate anions. Previous magnetometry measurements of KFe(C₂O₄)F indicate that it is a strongly interacting system with a Weiss constant θ ≈ −300 K that undergoes a magnetic ordering transition at T_N ≈ 20 K, yielding a frustration index, f = |θ|/T_N ≈ 15, reflective of high-spin frustration. We determine the nature of this frustrated antiferromagnetic ordering below T_N and show that the resulting magnetic structure is best described by a model in the Cmc′2₁′ magnetic space group.