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, [SiW11O39RuIII(Py)]5-

Ruthenium(III)-substituted a-Keggin-type silicotungstates with pyridine-based ligands, [SiW11O39RuIII(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 [SiW11O39RuIII(H2O)]5- with the pyridine derivatives in water at 80 degrees 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 L3-edge). Single-crystal X-ray analysis of compounds 2, 3, and 4 revealed that RuIII was incorporated in the a-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 p?p interaction of the pyridine moieties, whereas they existed as monomers in solution. CV indicated that the incorporated RuIIIPy was reversibly oxidized into the RuIVPy derivative and reduced into the RuIIPy derivative.