Syntheses and crystal structures of two sodium ruthenates: Na2RuO4 and Na2RuO3

Na2RuO4, prepared from Na2O2 and RuO2 via high oxygen pressure synthesis, crystallises monoclinic in space group P2(1)/c (a = 10.721(6), b = 7.033(4), c = 10.871(6) Angstrom, beta = 119.10(4)degrees, Z = 8, 2503 unique reflections, R-1 = 0.049). Structure determination from single crystal data shows that the compound consists of infinite chains of RuO5 trigonal bipyramids connected through their axial vertices. The Na cations connect the pseudohexagonally packed (1)(infinity)[RuO3O2/2] chains and are coordinated by six or seven oxygen atoms, respectively. The compound exhibits an one-dimensional spin system with mu = 2.80 mu(B) and Theta = -222 K and a three-dimensional antiferromagnetic ordering below 50 K. Na2RuO3 was obtained from Na2RuO4 at 850 degreesC under a flow of argon. The structure was determined from X-ray powder diffraction. It is closely related to the alpha-NaFeO2 and the Li2SnO3 structure types, layered variants of the NaCl type. In Na2RuO3 the Na and Ru atoms are partially disordered. This partially disordered state was approximated by a Rietveld refinement of two superimposed structural models (model I: R (3) over bar m, a = 3.12360(5), c = 16.0370(4) Angstrom, Z = 2; model II: C2/c, a = 5.4141(4), b = 9.3663(6), c = 10.8481(4) Angstrom, beta = 99.636(9)degrees, Z = 8)