SYNTHESIS, STRUCTURE, AND MAGNETIC-PROPERTIES OF (NH4)VOPO4 - A STRUCTURE WITH ONE-DIMENSIONAL CHAINS OF VO6 OCTAHEDRA

The title compound (NH4)VOPO4, (1), was synthesized hydrothermally from a mixture of CsVO3, V, CH3PO3H2, (NH4)2HPO4, (C2H5)3CH3NBr, and H2O in the mole ratios 3.96:1:4.88:11.97:4.96:1498. Phosphate (1) crystallizes in the orthorhombic space group Pnn2 with a = 10.5119(2) Å, b = 12.917(3) Å, c = 6.462(1) Å, V = 877.3(4) Å, Z = 4, and R = 0.043. The framework consists of one-dimensional chains of corner-sharing VO6 octahedra joined together by phosphate tetrahedra which generates cation filled tunnels running parallel to the c axis, There are two unique vanadium sites, with the VO6 octahedra connected to their neighbors through alternating cis -O-V-O and trans-O-V-O linkages. At higher temperatures, the compound is paramagnetic with isolated V4+d1 centers while complicated, short range antiferromagnetism is observed below 10 K. The framework is closely related to that of KVOPO4. © 1994 Academic Press, Inc.