Trilacunary Heteropolytungstates Functionalized by Organometallic Ruthenium(II), [(RuC₆H₆)₂XW₉O₃₄]^6- (X = Si, Ge)

The benzene−Ru(II)-supported trilacunary heteropolytungstates [(RuC6H6)2XW9O34]6- (X = Si, 1; Ge, 2) have been synthesized and characterized by multinuclear solution NMR (183W, 13C, 1H, 29Si), UV−vis and IR spectroscopy, electrochemistry, and elemental analysis. Single-crystal X-ray analysis was carried out on Rb2Na4[(RuC6H6)2SiW9O34]·21H2O (RbNa-1), which crystallizes in the triclinic system, space group P1̄, with a = 11.9415(2) Å, b = 13.3123(2) Å, c = 19.4927(4) Å, α = 96.6460(10)°, β = 95.1570(10)°, γ = 98.2560(10)°, and Z = 2 and on Cs2Na4[(RuC6H6)2GeW9O34]·19.5H2O (CsNa-2), which crystallizes also in the triclinic system, space group P1̄, with a = 11.930(4) Å, b = 13.353(4) Å, c = 19.586(6) Å, α = 95.982(5)°, β = 95.414(6)°, γ = 98.142(5)°, and Z = 2. The novel polyanion structure consists of two (RuC6H6) units linked to a trilacunary (XW9O34) Keggin fragment via Ru−O(W) and Ru−O(X) bonds resulting in an assembly with Cs symmetry. Polyanions 1 and 2 were synthesized by reaction of [RuC6H6Cl2]2 with [A-α-XW9O34]10- in aqueous buffer medium (pH 6.0). Both 1 and 2 are stable in solution as indicated by the expected 5-line pattern (2:1:2:2:2) in the 183W NMR and the expected 13C, 1H, and 29Si spectra. Descriptions of the respective electrochemical behaviors of the W centers and the Ru centers in 1 and 2 are given in media where these processes are clearly defined. In a pH = 3 acetate medium, the cyclic voltammetry of the W centers shows the known fingerprint of the trilacunary α-[XW9O34]n- (X = Ge, Si) moieties. The presence of the (RuC6H6) substituents imparts a good stability to these fragments in solution. Stepwise oxidation of the Ru centers was suspected in pH = 5 acetate medium, but only the first step was well-separated from a large current composite wave. The stepwise oxidation was finally observed clearly in a DMF−water (90/10 v/v) mixture and shows two well-behaved Ru oxidation processes. A short comparison is made with DMSO-bearing Ru polyoxometalates.