Stabilization of High-Valence Ruthenium with Silicotungstate Ligands: Preparation, Structural Characterization, and Redox Studies of Ruthenium(III)-Substituted alpha-Keggin-Type Silicotungstates with Pyridine Ligands, [SiW_(11)O_(39)Ru~(III)(Py)]~(5-)

摘要

Ruthenium(III)-substituted alpha-Keggin-type silicotungstates with pyridine-based ligands, [Si-W_(11)O_(39)Ru~(III)(Py)]~(5-), (Py: pyridine (1), 4-pyridine-carboxylic acid (2), 4,4'-bi-pyridine (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 deg 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 alpha-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 pi-pi 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.