PREPARATION OF AN ACID NIOBIUM PHOSPHATE AND ALKALI-METAL NIOBIUM PHOSPHATES, HAVING NBOPO4.H2O LAYERS CONDENSED WITH THE PHOSPHATE GROUP

New alkali-metal niobium phosphates and an acid niobium phosphate were prepared under low temperature hydrothermal conditions. Their chemical formulas were deduced to be NaNb2(OH)2(PO4)3.2.5H2O, KNb2(OH)2(PO4)3.nH2O, and HNb2(O-H)2(PO4)3.H2O, having lattice constants of a = 6.488 (2) angstrom and c = 16.286 (5) angstrom in the tetragonal system, a = 6.489 (3) angstrom, b = 6.452 (2) angstrom, c = 16.149 (6) angstrom, and beta = 95.63 (3)degrees in the monoclinic system, and a = 6.485 (2) angstrom, b = 6.415 (3) angstrom, c = 16.18 (2) angstrom, alpha = 90.11 (7)degrees, beta = 95.91 (5)degrees, and gamma = 90.95 (5)degrees in the triclinic system, respectively. They are isostructural, having a three-dimensional structural framework composed of NbO(H2O)(PO4) layers combined with PO4 groups. The alkali-metal ions and protons are exchangeable with other alkali-metal, alkaline-earth-metal, and alkylammonium ions. The acid niobium phosphate can intercalate n-alkylamines. The PO4 group that links the layers is removed upon ion exchange with certain ions and upon intercalation with certain amines, and the three-dimensional structure is transformed to a layered structure.