Metal-metal bonded Ru3+(μ-OR)2Ru3+ and Ru3.5+(μ-OR)2Ru3.5+ (R = CH3 and CH3CH2) compounds with tetrachlorocatecholate (Cl4Cat) have been synthesized in the corresponding alcohol, MeOH and EtOH, from a nonbridged Ru2+-Ru3+ compound, Na3[Ru2(Cl4Cat)4(THF)] ·3H2O·7THF (1). In alcohol solvents, compound 1 is continuously oxidized by oxygen to form Ru3+(μ-OR)2Ru3+ and Ru3.5+(μ-OR)2Ru3.5+ species. The presence of a characteristic countercation leads to selective isolation of either Ru3+(μ-OR)2Ru3+ or Ru3.5+(μ-OR)2Ru3.5+ as a stable adduct species. In methanol, Ph4PCl and dibenzo-18-crown-6-ether afford Ru3+ (μ-OMe)2Ru3+ species, [A]2[Ru2(Cl4Cat)4(μ-OMe) 2Na2(MeOH)6] ([A]+ = Ph4P+ (2), [Na(dibenzo-18-crown-6)(H2O)(MeOH)]+ (3)), while benzo-15-crown-5-ether provides a Ru3.5+ (μ-OMe)2Ru3.5+ species, [Na(benzo-15-crown-5)2][Ru2(Cl4Cat) 4(μ-OMe)2Na2(MeOH)6] (4). The air oxidation of 1 in a MeOH/EtOH mixed solvent (1:1 v/v) containing benzo-15-crown-5-ether provides a Ru3.5+(μ-OMe)2Ru3.5+ species, [Na(benzo-15-crown-5)(H2O)][Ru2(Cl4Cat) 2(μ-OMe)2Na2-(EtOH)2 (H2O)2(MeOH)2]·(benzo-15-crown-5) (5). Similarly, the oxidation of 1 in ethanol with Ph4PCl provides a Ru3.5+(μ-OEt)2Ru3.5+ species, (Ph4P)[Ru2(Cl4Cat)4(μ-OEt) 2Na2(EtOH)6] (7). A selective formation of a Ru3+(μ-OEt)2Ru3+ species, (Ph4P)2[Ru2(Cl4Cat) 4(μ-OEt)2Na2(EtOH)2 (H2O)2] (6), is found in the presence of pyrazine or 2,5-dimethylpyrazine. The crystal structures of these compounds, except 2 and 7, have been determined by X-ray crystallography, and all compounds have been characterized by several spectroscopic and magnetic investigations. The longer Ru-Ru bonds are found in the Ru3+(μ-OR)2Ru3+ species (2.606(1) and 2.628(2) Å for 3 and 6, respectively) compared with those of Ru3.5+(μ-OMe)2Ru3.5+ species (2.5260(6) Å and 2.514(2) Å for 4 and 5, respectively). These structural features and magnetic and ESR data revealed the electronic configurations of σ2π2δ*2δ 2π*2 and σ2π2δ*2 δ2π*1 for Ru3+(μ-OR)2Ru3+ and Ru3.5+(μ-OR)2Ru3.5+, respectively, in which the former is diamagnetic and the latter is paramagnetic with S = 1/2 ground state. Compound 5 forms a one-dimensional chain with alternating arrangement of a Ru3.5+ (μ-OMe)2Ru3.5+ unit and a free benzo-15 -crown-5-ether molecule by intermolecular hydrogen bonds (O(H2O)···O(crown-ether) = 2.91-3.04 Å). The cyclic voltammetry in DMF affords characteristic metal-origin voltammograms; two reversible and two quasi-reversible redox waves were observed. The feature of cyclic voltammograms for the Ru3+(μ-OR)2Ru3+ species (2, 3, and 6) and the Ru3.5+(μ-OR)2Ru3.5+ species (4 and 7) are similar to each other, indicating that both species are electrochemically stable. The isolation of the pyrazine-trans-coordinated species, [Ph4P][Ru(Cl4Cat)2(L)2] (L = pyrazine (8), 2,5-dimethylpyrazine (9)), revealed the selective isolation of 6 from pyrazine-containing solution. UV-vis spectral variation by ethanolysis for 9 demonstrated the selective conversion from the pyrazine-trans-coordinated species to the Ru3+(μ-OEt)2Ru3+ species without an oxidation to the Ru3.5+(μ-OEt)2Ru3.5+ species. This result suggests the presence of equilibrium between [Ru(Cl4Cat)2(L)2]- and Ru3+(μ-OEt)2Ru3+ species in the synthetic condition for 6.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry