Hydrothermal synthesis, crystal structure, and magnetic properties of Cs[(V₂O₃)(HPO₄)₂(H₂O)], a mixed-valence vanadium (IV, V) hydrogen phosphate with a one-dimensional (-V^IV-O-V^V-O-) chain of corner-sharing VO₆ octahedra

The hydrothermal reaction of Cs₄V₂O₇, V, H₃PO₄, H₂O, and Bu₄NBr in the molar ratio 4.5:1:41:3150:1 at 200°C for 48 hr yielded the red-brown cesium vanadium phosphate Cs[(V₂O₃) (HPO₄)₂(H₂O)], a mixed-valence V(IV, V) species. The structure contains corner-sharing vanadium octahedra and phosphorus tetrahedra with unusual 1-D (-V^IV-O-V^V-O-)∞ chains formed from VO₆ octahedra sharing opposite corners. These chains are connected through tridentate bridging (HPO₄)^2- units to produce a three-dimensional network. The Cs⁺ cations occupy large channels formed from six vanadium octahedra and six phosphorus tetrahedra. At room temperature the material is paramagnetic with one unpaired spin per (-V^IV-O-V^V-O-) unit while complicated antiferromagnetic ordering is observed below ca. 6 K. Crystal data: monoclinic, P 2₁/n with a = 7.22(1), b = 18.56(1), c = 8.195(6) Å, β = 114.01(6)°, Z = 4, d_calc = 3.233 g cm^-3; structure solution and refinement based on 1088 reflections converged at R = 0.028.