Crystal structure, oxidation state and magnetism of La1.2Sr2.4RuO7:: a new member of the [A2O][AnBn-1O3n ] series of hexagonal perovskites

Single crystals of the new compound La1.2Sr2.4RuO7, an oxide related to the hexagonal perovskites, were grown from a BaCl2 flux. The structure was solved by single crystal X-ray diffraction. La1.2Sr2.4RuO7 crystallizes in the space group R (3) over barm with a = 5.760(1) Angstrom and c = 18.273(3) Angstrom. It is one of the rare examples of oxides with isolated RuO6-octahedra. The structure consists of alternating layers of RuO6-octahedra and trigonal (La,Sr)O-6-prisnis. These prisms are capped by one additional oxygen ion, which occupies a distorted position within the (La,Sr)O-6-Iayers. La1.2Sr2.4RuO7 is the second member of the general [A(2)O][A(n)B(n-1)O(3n)] family of hexagonal perovskites with n = 2 and the first ruthenate possessing this structure. XANES investigations, bond valence sum calculations and magnetic measurements show that ruthenium takes the oxidation state + 5. Although the ruthenium ions have quite long distances. a Medium strong antiferromagnetic interaction between these paramagnetic centers was observed. (C) 2003 Elsevier Inc. All rights reserved.