Magnetism and 3D Electron Diffraction Solution of Hydrated Rubidium–Ruthenium Oxide Rb ₂ Ru ₂ O ₇ ·H ₂ O

The crystal structure of Rb₂Ru₂O₇·H₂O was determined by three-dimensional electron diffraction from the individual crystallites of a solid-state powder product. Rb₂Ru₂O₇·H₂O crystallizes in space group <i>C</i>2/<i>c</i> (<i>a</i> = 7.841(3) Å, <i>b</i> = 12.500(3) Å, <i>c</i> = 8.392(2) Å, β = 93.57(4)°, Z = 4). The structure contains infinite chains that run normal to the (101) plane and consist of alternating RuO₆ octahedra and square-pyramidal RuO₅ units connected via shared O-O edges. Magnetic properties were measured on the bulk powder, showing a diamagnetic baseline from 300 K to 60 K with a small Curie tail below 55 K. The magnetic moment, calculated from the 1.8 K isotherm, saturates at <i>M</i> = 4.4 × 10^-3 μ_B Ru^-1, much less than would be expected for <i>S</i> = 1 ruthenium. Bond-valence-sum analysis indicates high-valent Ru, and the near-diamagnetic response is consistent with the edge-sharing Ru-Ru motif, where weak direct Ru-Ru overlap yields a local singlet.