A vanadium (V) monophosphate with a tunnel structure: KV2O4PO4

A vanadium (V) monophosphate, KV2O4PO4, with an original tunnel structure h as been synthesized. It crystallizes in the space group Pn2(1)a, with n 13. 9241(1) Angstrom, b = 19.946(1) Angstrom, 4.749(1) Angstrom. The [V2PO8](in finity) framework consists of 90 degrees oriented [V2O8](infinity) pyramida l chains running along a and c, respectively, interconnected by single PO, tetrahedra. This framework delimits two sets of tunnels: large S-shaped and smaller eight-sided tunnels running along c and a respectively. The K+ cat ions are located approximately at the intersection of these tunnels, with a n eight- and nine-fold coordination, respectively. The geometry of the chai ns of corner-sharing VO5 pyramids is compared to those of the octahedral ch ains in the perovskite and hexagonal tungsten bronze structures. The existe nce of two abnormally short V-O bonds per pyramid is emphasized and discuss ed. (C) 1999 Academic Press.