K3Na(RuO4)2 and Rb3Na(RuO4)2, two new ruthenates with glaserite structure

K3Na(RuO4)2 and Rb3Na(RuO4)2 were prepared by solid state reactions of RuO2, Na2O2, and RbO2 or KO2, respectively, at 873 K under oxygen pressure. K3Na(RuO4)2 performs a structural transition at 467 K and transforms from a monoclinic form at room temperature (C2/cC2/c, a=10.323(8)a=10.323(8), b=5.989(4)b=5.989(4), c=15.278(7) Åc=15.278(7) Å, β=90.49(5)°β=90.49(5)°, Z=4Z=4, single crystal data, 1231 independent reflections, R1=4.27%R1=4.27%, wR2=8.95%wR2=8.95%) into a trigonal high temperature modification (Rietveld refinement from X-ray powder data, P3¯m1, a=6.0164(1)a=6.0164(1), c=7.6855(2) Åc=7.6855(2) Å, Z=1Z=1, 4053 data points, Rp=6.63%Rp=6.63%, wRp=8.65%wRp=8.65%) which is isotypic to glaserite, K3Na(SO4)2. The rubidium analogue, Rb3Na(RuO4)2, does not show a phase transition down to 100 K. According to the structure determination from single crystal X-ray data, Rb3Na(RuO4)2 (P3¯m1, a=6.0784(3)a=6.0784(3), c=7.8994(6) Åc=7.8994(6) Å, Z=1Z=1, 281 independent reflections, R1=2.35%R1=2.35%, wR2=5.51%wR2=5.51%) is isotypic to glaserite and the HT phase of K3Na(RuO4)2. The magnetic measurements confirm the presence of hexavalent ruthenium displaying paramagnetic behaviour along with antiferromagnetic interactions at lower temperatures. The Raman measurements also confirm the tetrahedral coordination of ruthenium with oxygen.

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