Synthesis, Crystal Structure, and Magnetism in Fluoride Sulfates, A₂VF₃(SO₄) (A = K, Rb, Cs)

Three novel alkali metal vanadium(III) fluoride sulfates, A2VF3(SO4) (A = K, Rb, Cs), were prepared through hydrothermal redox reactions. The products were isostructural with previously reported K2MnF3(SeO4) and featured one-dimensional chains of trans-VF4O2 octahedra that were connected by μ2-bridging oxygen atoms with SO4 units. In the title compounds, spin chains of V3+ (S = 1) with trans V–F–V bridges were arranged in a two-dimensional rectangular lattice. DC magnetization showed unpredictable ferromagnetic-like ordering at ∼0.6 K, accompanied by a weak hysteresis curve. At high temperatures, the dominant magnetic interactions were found to be antiferromagnetic, as deduced from the negative values of the Curie–Weiss temperature.