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, [SiW₁₁O₃₉Ru^III(Py)]⁵⁻

Abstract

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 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.

Preparation of tetrabutylammonium salt of a mono-Ru(iii)-substituted α-Keggin-type silicotungstate with a 4,4′-bipyridine ligand and its electrochemical behaviour in organic solvents

“…1b), while bipyridine moieties in the crystal of caesium salts were linked via π-π stacking interactions of bipyridine. 9 The torsion angles of two pyridine rings in the crystal of 1 were 36.12 º (∠C(5)-C(1)-C(6)-C(10)) and 36.79 º 55 (∠C(2)-C(1)-C(6)-C (7)), which were significantly larger than those in the crystal of caesium salt (10.79 º and 17.07 º). An asymmetric unit contained two polyanions, ten tetrabutylammonium cations (Bu 4 N + ) and seven crystallization CH 3 CN molecules.…”

“…15 Homemade de-ionized water (Millipore, Elix) was used. The compound Cs 5 [α-SiW 11 O 39 Ru III (bipy)]·8H 2 O (bipy: 4,4'bipyridine) was prepared according to the published procedure 9 and analysed by CV, IR and UV-Vis.…”

Reactivity of a (Benzene)Ruthenium(II) Cation on a Di‐lacunary γ‐Keggin‐Type Silicotungstate and Synthesis of a Mono‐(Benzene)Ruthenium(II)‐Attached γ‐Keggin‐Type Silicotungstate

“…The reversible redox couple is assignable to the two‐electron redox couple on W, and the oxidation peak is assignable to oxidation of Ru. The oxidation potential of Ru is higher than that of the other Ru‐containing silicotungstates, such as mono‐Ru substituted silicotungstate derivatives {[SiW 11 O 39 Ru(L)] n – , L = H 2 O, CO, pyridine, DMSO}, and a tetra‐Ru‐containing sandwiched compound, [(γ‐SiW 10 O 36 ) 2 {Ru 4 O 4 (OH) 4 (H 2 O) 4 }] 10– …”

Recent Progress in the Application of Polyoxometalates for Dye‐sensitized/Organic Solar Cells

“…[1][2][3] The metal atoms that make up the framework are termed the addenda atoms and they are usually group 5 or group 6 transition metals in their high oxidation states, for example vanadium, niobium, tantalum, molybdenum, tungsten, etc. If the POM is condensed from the same inorganic acids, it is named iso-polyoxometalate; If not, the POM is named hetero-polyoxometalate.…”