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 (-VIV-O-VV-O-) Chain of Corner-Sharing VO6 Octahedra

Abstract

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 (-VIV-O-VV-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 (-VIV-O-VV-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, dcalc = 3.233 g cm-3; structure solution and refinement based on 1088 reflections converged at R = 0.028.