Figure 2.

Crystal structures of β- and γ-Cu₂V₂O₇. (a) and (b) β- and γ-Cu₂V₂O₇ structures, respectively, projected along their c-axes, oriented so that the V–V vectors (red lines) of both structures are mutually parallel on the page. (c) and (d) β- and γ-Cu₂V₂O₇ structures, respectively, projected along their ab-planes. Blue (and orange) polyhedra correspond to penta-coordinated CuO₅ units. Green polyhedra correspond to hexa-coordinated CuO₆ units. Red spheres represent vanadium atoms. For the sake of clarity, the VO₄ tetrahedra and the oxygen atoms, which correspond to the vertices of all coordination complexes, are not shown. Blue, orange, and green vectors show the crystallographic direction of the chains. The black axes represent the principal compression axes (discussed in the compressibility section). The crystal structures were rendered in Vesta.⁴⁰ Supplementary crystallographic data for both β- and γ-Cu₂V₂O₇ structures can be obtained free of charge from the Cambridge Crystallographic Data Centre (CCDC) under deposition numbers 2123194–2123205.