Preparation and some properties of vanadium(III) tris(metaphosphate) and vanadium(IV) bis(metaphosphate)

Abstract

Vanadium(IV) bis(metaphosphate), [VO][PO₃]₂(d¹), and vanadium(III) tris(metaphosphate), V[PO₃]₃(d²). have been prepared by heating V₂O₅ in phosphoric acid. Blue crystals of [VO][PO₃]₂ are tetragonal, space group I4₁md, with lattice parameters a₀= 10.973(10), c₀= 4.293(4)Å, and Z= 4. Green crystals of V[PO₃]₃ are monoclinic, space group Cc, with lattice parameters a₀= 13.19(1), b₀= 19.08(2), c₀= 9.42(1)Å, β= 127° 08(6)′, and Z= 12. The bis(phosphate) probably contains chains of corner-shared [VO₆]^8– octahedra linked by metaphosphate ([PO₃]^–)_∞ chains. The tris(phosphate) is structurally similar to the C-type metaphosphates of Mo, Ti, Cr, Fe, and Al. Both compounds are resistant to most solvents and stable in air to at least 1 000 °C and have been characterised by magnetic-susceptibility and electronic-spectral measurements. Neither compound shows magnetic ordering down to 1.5 K. Possible non-linear optical properties of [VO][PO₃]₂ are mentioned.