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(11) O(39) Ru(III) (Py)](5-)
Ruthenium(III)-substituted α-Keggin-type silicotungstates with pyridine-based ligands, [SiW(11) O(39) Ru(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(11) O(39) Ru(III) (H(2) O)](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 (1) H 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 RuN bond. In the solid state, compounds 2 and 3 formed a dimer through ππ 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.