PHOSPHATE NIOBIUM BRONZES AND BRONZOIDS WITH THE MPTBP STRUCTURE - NA4NB8P4O32 AND NA4-XAXNB7MP4O32 4TH MEMBERS OF THE SERIES AX(PO2)4(NBO3)2M

Nine new phosphate niobium bronzes and bronzoids have been synthesized Na4Nb8P4O32, Na3CaNb7MP4O32 (M = Ti, Zr, Sn), Na2Ca2Nb7MP4O32 (M = Al, Fe), Na3ANb7TiP4O32 (A = Sr, Ba) and Na3BaNb8P4O32. They crystallize in a monoclinic cell, space group P2(1), a almost-equal-to 6.6 angstrom, b almost-equal-to 5.3 angstrom, c almost-equal-to 18 angstrom, beta almost-equal-to 90.4 angstrom. The structure of one of them, Na4Nb8P4O32, has been determined from an X-ray single crystal study. They all belong to the same structural type, i.e. they represent the fourth member of the series Nax(PO2)4(NbO3)2m. Their host lattice [P4Nb8O32] infinity is isotypic with the monophosphate bronze with pentagonal tunnels (MPTBp): P4W8O32. It consists of ReO3-type layers which are four octahedra wide and linked though monophosphate groups. At the junction between two octahedral layers, the phosphate groups form pentagonal tunnels where the Na+ cations are located.