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 C2/c (a = 7.841(3) Å, b = 12.500(3) Å, c = 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 M = 4.4 × 10⁻³ μB Ru⁻¹, much less than would be expected for S = 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.