Enthalpy of Interaction and Activation Energy for Thermal Degradation of Modified Forms of Lamellar Titanium Hydrogenphosphate

A vanadium (V) monophosphate, KV2O4PO4, with an original tunnel structure has been synthesized. It crystallizes in the space group Pn21a, with a=13.924(1) ?, b=19.946(1) ?, c=4.749(1) ?. The [V2PO8] framework consists of 90° oriented [V2O8] pyramidal chains running along a and c, respectively, interconnected by single PO4 tetrahedra. This framework delimits two sets of tunnels: large S-shaped and smaller eight-sided tunnels running along c and a respectively. The K+ cations are located approximately at the intersection of these tunnels, with an eight- and nine-fold coordination, respectively. The geometry of the chains of corner-sharing VO5 pyramids is compared to those of the octahedral chains in the perovskite and hexagonal tungsten bronze structures. The existence of two abnormally short V–O bonds per pyramid is emphasized and discussed.