STRUCTURE DETERMINATION OF NA2PDP2O7 FROM X-RAY-POWDER DIFFRACTION

Na2PdP2O7 crystal structure was solved by direct methods and refined by the Rietveld technique from X-ray powder diffraction data. The cell is monoclinic (space group C 2/c, Z = 4) with a = 14.693(3) angstrom, b = 5.8551(4) angstrom, c = 7.922(2) angstrom and beta = 114.11(2)-degrees. The refinement ot 37 parameters using 45 reflections leads to R(B) = 0.045 and R(WP) = 0.105. The structure of Na2PdP2O7 can be described by the alternative (1 0 0) stacking of layers containing NaO6 octahedra, and ribbons formed by P2O7 groups with twofold internal symmetry and PdO4 square planes. The ribbons are built up from blocks [PdP2O9] which lead to a new crystal chemistry for diphosphates. In the layers, the cationic network adopts a honeycomb plane net, whereas oxygens exhibit [3.4.5.4,(3.4.5(2))2] plane nets.