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 La_1.2Sr_2.4RuO₇, an oxide related to the hexagonal perovskites, were grown from a BaCl₂ flux. The structure was solved by single crystal X-ray diffraction. La_1.2Sr_2.4RuO₇ crystallizes in the space group with a=5.760(1) Å and c=18.273(3) Å. 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)O₆-prisms. These prisms are capped by one additional oxygen ion, which occupies a distorted position within the (La,Sr)O₆-layers. La_1.2Sr_2.4RuO₇ is the second member of the general A₂O]A_nB_n−1O_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.