Synthesis and Crystal Structure of σ-Zn0.25V2O5· H2O with a Novel Type of V2O5Layer

A new layered vanadium bronze designated as σ-phase Zn0.25V2O5· H2O has been hydrothermally synthesized from ZnCl2and VO(OH)2. A single-crystal study revealed the triclinic systemP1:a= 10.614(2) Å,b= 8.031(3) Å,c= 10.7688(9) Å, α = 90.65(1)°, β = 91.14(1)°, γ = 90.09(2)°, andZ= 8. The structure was solved and refined toR/Rw= 0.079/0.048 for 1580 reflections withI> 3σ(I), which consists of V2O5layers stacking along thecaxis and interstitial hydrated Zn2+ions. The V2O5layer adopts a novel polyhedral framework built up of VO6octahedra, VO5trigonal bipyramids, and VO4tetrahedra. When projected parallel to theabplane, the V2O5layer is described by the atomic sheet model in a manner similar to the V2O5layer of δ phase such as δ-AgxV2O5, that is, a double-sheet type composed of two V2O5sheets facing each other. The interstitial Zn atom forms a ZnO6octahedron with two apical oxygens of the VO4tetrahedra on opposide sides and with four coplanar water molecules. The anhydrous σ phase was obtained by heating the hydrate up to 200°C accompanied by the contraction in layer spacing from 10.76 to 8.92 Å.