The role of temperature in the solvothermal synthesis of hybrid vanadium oxyfluorides

Abstract

The solvothermal synthesis of a new series of organically templated vanadium oxyfluorides is presented. The materials were synthesised from identical starting mixtures using temperature as the only independent variable. This shows a trend towards increasing dimensionality and decreasing vanadium oxidation state as a function of temperature. The materials were synthesised from a system containing V₂O₅–HF–H₂O–ethylene glycol–piperazine which resulted in four new structure types, together with a previously known phase. [C₄N₂H₁₂]₃[V₂O₂F₈][VOF₄(H₂O)]₂ (1) consists of V^(V)-centred monomeric units and V^(IV) edge-sharing dimers, which are held together by hydrogen bonding to form infinite chains. [C₄N₂H₁₂]₄[V₄O₃F₁₇]·4H₂O (2) features a Y-shaped tetramer containing both V^(III) and V^(IV)-centred octahedra which are held together via hydrogen bonding from the water molecules to form infinite sheets. [C₄N₂H₁₂]₄[V₅O₃F₂₀]·2H₂O (3) is a complex chain containing five different V-centred octahedra, which shares structural similarities with compound (2). The inter-relations between these three structure types as a function of temperature, together with two further compounds isolated from this system, are discussed.