Synthesis and crystal structure of the palladium oxides NaPd3O4, Na2PdO3 and K3Pd2O4

摘要

NaPd3O4, Na2PdO3 and K3Pd2O4 have been prepared by solid-state reaction of NaO, or KO2 and PdO in sealed silica tubes. Crystal structures of the synthesized phases were refined by the Rietveld method from X-ray powder diffraction data. NaPd3O4 (space group Pm3n, a = 5.64979(6) angstrom, Z = 2) is isostructural to NaPt3O4. It consists of NaO8 cubes and PdO4 squares, corner linked into a three-dimensional framework where the planes of neighboring PdO4 squares are perpendicular to each other. Na2PdO3 (space group C2/c, a = 5.3857(1) angstrom, b = 9.3297(1)angstrom, c = 10.8136(2) angstrom, beta = 99.437(2)degrees, Z = 8) belongs to the Li2RuO3-structure type, being the layered variant of the NaCl structure, where the layers of octahedral interstices filled with Na+ and Pd4+ cations alternate with Na-3 layers along the c-axis. Na2PdO3 exhibits a stacking disorder, detected by electron diffraction and Rietveld refinement. K3Pd2O4, prepared for the first time, crystallizes in the orthorhoinbic space group Cmcm (a = 6.1751(6) angstrom, b = 9.1772(12) angstrom, c = 11.3402(12) A, Z = 4). Its structure is composed of planar PdO4 units connected via common edges to form parallel staggered PdO2 strips, where potassium atoms are located between them. Magnetic susceptibility measurements of K3Pd2O4 reveal a Curie-Weiss behavior in the temperature range above 80 K. (C) 2007 Elsevier Inc. All rights reserved.