The dimeric [V₂O₄F₆]^4- vanadium oxide-fluoride anion in Na₂(M(H₂O)₂)(V ₂O₄F₆) (M= Co²⁺, Ni²⁺, and Cu²⁺)

Three new vanadium oxide-fluoride phases, Na₂(M(H ₂O)₂)(V₂O₄F₆) (M= Co ²⁺, Ni²⁺, and Cu²⁺), were prepared by hydrothermal techniques in hydrofluoric acid. The compounds contain the dioxo vanadium fluoride dimeric anion: [V₂O₄F₆] ^4-. The harder (Na⁺) and softer (M = Co²⁺, Ni²⁺, and Cu²⁺) cations coordinate to the harder fluoride and softer oxide anions, respectively. In contrast to monoxo vanadium fluorides, the dioxo vanadium fluoride exhibits an increased nucleophilicity of the oxide anions. This increased nucleophilicity allows the anion to bond covalently with late transition metals to form 2D layers that contain both an early transition metal (V5⁺) and a late transition metal (Co²⁺, Ni ²⁺, or Cu²⁺).