Synthetic strategies for new vanadium oxyfluorides containing novel building blocks: structures of V(iv) and V(v) containing Sr4V3O5F13, Pb7V4O8F18, Pb2VO2F5, and Pb2VOF6

Abstract

Four new vanadium oxyfluorides (VOFs), Sr₄V₃O₅F₁₃ (1), Pb₇V₄O₈F₁₈ (2), Pb₂VO₂F₅ (3), and Pb₂VOF₆ (4), have been synthesized under mild hydrothermal conditions. The choice of starting reagents, AF₂ or A(CH₃CO₂)₂·xH₂O (A = Pb, alkaline earth), determined the oxidation states of vanadium in the final products. The reaction of V₂O₅ with AF₂ leads, consistently, to the formation of V(V) compounds, while the use of A(CH₃CO₂)₂·xH₂O results in V(IV) containing compounds, suggesting that the acetate species behaves as an effective mild reducing agent. The crystal structures, characterized by single crystal X-ray diffraction, revealed that the compounds exhibit various anionic VOF building blocks, including dimeric and trinuclear units, as well as one-dimensional chains. All compounds contain fluorine atoms that are not bonded to the vanadium atoms, which are located between two-dimensional layers consisting of corner- or edge-shared FA₃ or FA₄ polyhedra that separate the vanadium containing building blocks. The magnetic susceptibility data for 4 were measured as a function of temperature, yielding an effective magnetic moment of 1.72 μ_B that confirms the presence of V(IV). UV-vis reflectance and thermal properties were also characterized.