SYNTHESIS AND STRUCTURAL INVESTIGATION OF A NEW POTASSIUM VANADIUM-OXIDE BRONZE - RHO-K0.50V2O5

ρ{variant}-K0.50V2O5, synthesized at 350°C by interaction of K2C2O4 on V2O5, crystallizes in the orthorhombic system, space groupCmcm, with the cell parametersa = 3.674(1)A °,b = 11.607(3)A °,c = 18.670(8)A °,V = 756.20(4)A °3, andZ = 8. Despite the poor quality of the single crystal obtained, structural determination gave anR factor of 0.067 for 498 reflections. The original layer structure of ρ{variant}-K0.50V2O5 exhibits [V2O5]n sheets built up by four VO6 octahedra sharing edges and making quadruple endless strings associated by edges along [100]. These sheets, depicted as double layers D4, and their mirror image D4M alternate along [001]. The intercalated potassium atoms hold together the [V2O5]n layers. They partially occupy two sites, 80% in K1 at the center of an oxygenated rectangular prism (CN8) and 20% in K2 surrounded by six oxygen atoms forming a trigonal prism (CN6). K1O8 and K2O6 polyhedra share a rectangular face, with the short distance between the potassium sites preventing simultaneous occupancy. The K2 site occupancy is related to an electronic localization within the [V2O5]n layers. Finally, a comparison is made with other prototype structures containing D4 layers like δ- and ν-KxV2O5 phases. © 1992 Academic Press, Inc. All rights reserved.