A NEW MIXED-VALENT VANADIUM PHOSPHATE WITH A TUNNEL STRUCTURE - CD5V3P6O25

A new mixed-valent phosphate Cd5V3P6O25 was isolated and its structure was determined from single-crystal X-ray diffraction data. This phase crystallizes in the monoclinic space group C2/c with a = 15.861(1) Å, b = 4.710(1) Å, c = 24.160(2) Å, β = 103.07(1)°, V = 1868.9(5) Å3, Z = 4, R = 0.029, Rw = 0.034 for 2626 unique reflections with I > 3σ(I). The structure consists of VO5 pyramids and VO6 octahedra occupied by V(IV) and V(III), respectively, and connected through monophosphate groups. The VO5 pyramids exhibit one abnormally short V-O distance characteristic of the vanadyl ion and form columns parallel to b. The [V3P6O25]∞ framework can be described as built up from mixed double chains [V2P6O24]∞ of corner-sharing octahedra and PO4 tetrahedra running along b; the latter are connected to each other through VO5 pyramids, located in planes parallel to (001). This host lattice forms tunnels running along b where the cadmium ions are located. The latter exhibit a distorted octahedral coordination. © 1993 Academic Press, Inc.