Stabilization of high-valence ruthenium with silicotungstate ligands: Preparation, structural characterization, and redox studies of ruthenium(III)-substituted α-keggin-type silicotungstates with pyridine ligands, [SiW ₁₁O ₃₉Ru ^III(Py)] ^5-

Ruthenium(III)-substituted α-Keggin-type silicotungstates with pyridine-based ligands, [SiW ₁₁O ₃₉Ru ^III(Py)] ^5-, (Py: pyridine (1), 4-pyridine-carboxylic acid (2), 4,4'-bipyridine (3), 4-pyridine-acetamide (4), and 4-pyridine-methanol (5)) were prepared by reacting [SiW ₁₁O ₃₉Ru ^III(H ₂O)] ^5- with the pyridine derivatives in water at 80°C and then isolated as their hydrated cesium salts. These compounds were characterized using cyclic voltammetry (CV), UV/Vis, IR, and ¹H NMR spectroscopy, elemental analysis, titration, and X-ray absorption near-edge structure (XANES) analysis (Ru K-edge and L ₃-edge). Single-crystal X-ray analysis of compounds 2, 3, and 4 revealed that Ru ^III was incorporated in the α-Keggin framework and was coordinated by pyridine derivatives through a Ru-N bond. In the solid state, compounds 2 and 3 formed a dimer through π-π interaction of the pyridine moieties, whereas they existed as monomers in solution. CV indicated that the incorporated Ru ^III-Py was reversibly oxidized into the Ru ^IV-Py derivative and reduced into the Ru ^II-Py derivative.