Ruthenium(V) oxides from low-temperature hydrothermal synthesis

Low-temperature (200 C) hydrothermal synthesis of the ruthenium oxides Ca_1.5Ru₂O₇, SrRu₂O₆, and Ba₂Ru₃O₉(OH) is reported. Ca_1.5Ru₂O₇ is a defective pyrochlore containing Ru^V/VI; SrRu₂O₆ is a layered Ru^V oxide with a PbSb₂O₆ structure, whilst Ba₂Ru₃O₉(OH) has a previously unreported structure type with orthorhombic symmetry solved from synchrotron X-ray and neutron powder diffraction. SrRu₂O₆ exhibits unusually high-temperature magnetic order, with antiferromagnetism persisting to at least 500 K, and refinement using room temperature neutron powder diffraction data provides the magnetic structure. All three ruthenates are metastable and readily collapse to mixtures of other oxides upon heating in air at temperatures around 300-500 C, suggesting they would be difficult, if not impossible, to isolate under conventional high-temperature solid-state synthesis conditions. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)