Syntheses and Crystal Structures of Two Sodium Ruthenates: Na 2 RuO 4 and Na 2 RuO 3

Na 2 RuO 4 , prepared from Na 2 O 2 and RuO 2 via high oxygen pressure synthesis, crystallises monoclinic in space group P 2 1 /c ( a = 10.721(6), b = 7.033(4), c = 10.871(6) Å, β = 119.10(4)°, Z = 8, 2503 unique reflections, R 1 = 0.049). Structure determination from single crystal data shows that the compound consists of infinite chains of RuO 5 trigonal bipyramids connected through their axial vertices. The Na cations connect the pseudohexagonally packed   ∞ 1 [RuO 3 O 2/2 ] chains and are coordinated by six or seven oxygen atoms, respectively. The compound exhibits an one‐dimensional spin system with μ = 2.80 μ B and Θ = —222 K and a three‐dimensional antiferromagnetic ordering below 50 K. Na 2 RuO 3 was obtained from Na 2 RuO 4 at 850 °C under a flow of argon. The structure was determined from X‐ray powder diffraction. It is closely related to the α‐NaFeO 2 and the Li 2 SnO 3 structure types, layered variants of the NaCl type. In Na 2 RuO 3 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¯ m , a = 3.12360(5), c = 16.0370(4) Å, Z = 2; model II: C2/c , a = 5.4141(4), b = 9.3663(6), c = 10.8481(4) Å, β = 99.636(9)°, Z = 8).