LANGBEINITE, A HOST LATTICE FOR V3O CLUSTERS - THE TRIVALENT VANADIUM PHOSPHATE K11V15P18O73

During the study of the KVPO system, crystals of a new phase, K11V15P18O73, were isolated. This phase crystallizes in the space group P213 with a = 9.896(1) Å. Its structure was refined from single-crystal X-ray data, using 561 reflections, leading to agreement factors R = 0.030 and Rw = 0.034. It consists of a langbeinite-type framework, [V12P18O72]∝, whose cages are occupied by K+ ions and "V3O" clusters according to the formulation K11(V3O)(V12P18O72). In these cages, the six K(1) sites of the classical langbeinite structure are fully occupied by potassium, whereas one K(2) site out of six is replaced by an oxygen atom O(5). Three vanadium atoms are then inserted around this additional oxygen, forming three additional VO6 octahedra sharing this common O(5) oxygen. Moreover, each of these additional VO6 octahedra shares one edge with a PO4 tetrahedron, and one face and one edge with two VO6 octahedra, respectively, of the [V12P18O72]∝ host lattice. The interatomic distances are discussed. © 1992.