Na 2VP 2O 8: A tetravalent vanadium diphosphate with a layered structure

Abstract

A new vanadium(IV) diphosphate, Na 2VP 2O 8, was isolated and its structure was determined from single-crystal X-ray diffraction data. This phase crystallizes in the monoclinic space group P2 1/c, with a = 7.7178(6)A˚, b = 13.3233(8)A˚, c = 6.2871(3)A˚, β = 99.49(1)°. This structure consists of [VP 2O 8] ∞ layers parallel to (010), sandwiching sodium cations. The layers can be described either by [VP 2O 11] units or by [VPO 8] ∞ chains running along c. The [VP 2O 11] units are built up from a P 2O 7 group sharing two of its apices with a VO 6 octahedron, whereas in the [VPO 8] ∞ chains one VO 6 octahedron alternates with one PO 4 tetrahedron. An important feature of this structure deals with the existence of one free oxygen atom for each VO 6 octahedron and for each P 2O 7 group, pointing out the slabs. The VO 6 octahedron exhibits one abnormally short V-O bond characteristic of the vanadium(IV) ion.