SYNTHESIS AND STRUCTURE OF RBVP2S7 - A NEW THIOPHOSPHATE IN THE M(I)-V-P-S FAMILY

RbVP2S7 has been obtained as black platelets by heating the elements in stoichiometric proportions at 550°C under vacuum in evacuated silica tubes for 21 days. It crystallizes in the monoclinic symmetry, space group C2, with the parameters a = 858.30(9) pm, b = 956.8(1) pm, c = 646.94(3) pm, and β = 98.22(1)°, V = 525.8(1) × 106pm3. The refinements led to a reliability factor of 2.7% for 933 independent reflections and 56 variables. The structure of RbVP2S7 is built from VS6 octahedra and PS4 tetrahedra. The tetrahedra, which form P2S7 groups through apex sharing, bind the VS6 octahedra through mutual apexes or edges. The rubidium atom occupies the center of a sulfur bicapped trigonal prism, thus exhibiting a coordination of eight. Within its site, the rubidium important displacement can only be described by using a third-order artharmonic tensor (Prometheus program). The atomic distances and magnetic properties are in agreement with the RbIVIII(P2S7)-IV charge balance. © 1993 Academic Press, Inc.