Blue dimer

Fig. 9.7 Time-absorption profile of the spectra shown above at 1010 nm to monitor the formation of the radical-ion-pair state (blue = monomer 9b, light blue = dimer 9c)...

Liu F, Concepcion JJ, Jurss JW, Cardolaccia T, Templeton JL, Meyer TJ. Mechanisms of water oxidation from the blue dimer to photosystem II. Inorg Chem. 2008 47(6) 1727-52. 

The blue dimer c/s,c/s[(bpy)2(H20)Ru(III)0Ru(III)(0H2)bpy)2] (Fig. 7) was among the first molecular species to show catalyzed water oxidation by Ce(lV) through a reaction mechanism which has been elucidated in detail by spectroscopic, electrochemical, and chemical mixing experiments [18] (Scheme 1). The key point... 

As a catalyst, the blue dimer has limitations due to oxidatively induced coordination of anions which slow down the catalytic cycles. Since the 0-0 bond forming step occurs at a single Ru(V) site, it has been demonstrated that simpler and more robust mononuclear Ru(lll) aquo complexes of the type [Ru(tpy)(bpm)(H20)] , where tpy is the 2,2 6 2" terpyridine and bpm is the bipyrimidine ligand, can undergo hundreds of turnovers without showing decomposition according to the cycle schematized in Scheme 2 [20]. It must be noted that the Ru(III) state appears to be a missing state due to instability toward the disproportionation to Ru(IV) and Ru(II). 

Although the electrocatalytic water oxidation by blue dimer has been demonstrated at FTO and ITO electrodes modified with phosphonated Ru(ll)... 

The first synthetic, non-proteic molecular catalyst capable to oxidize water was reported about 30 years ago [69]. This was the so-called blue dimer, [(bpy)2Ru (H20)(p-0)Ru(H20)G>py)2] - Once electrochemically or chemically activated, the blue dimer undergoes the stepwise loss of four electrcms and four protons, producing an intermediate reactive species that oxidizes water [70,71]. Unfortunately, the blue dimer loses its catalytic efficiency after a few cycles due to the degradation of the organic ligands. However, the blue dimer paved the way to the discovery of other water oxidation catalysts, most of them still based on ruthenium centers [72—78]. In the last few years, molecular catalysts based on iridium centers [79] as well as on cheaper metals such as manganese [80-84], cobalt [85], and iron [86] were also developed. 

One of the most significant attempts to heterogenize a molecular WOC regarded the immobilization of a phosphonate-modified blue dimer onto ITO or nanocrystalline Ti02 and Zr02. The catalyst retains its water oxidation ability on the electrodes surface, as well as its proton-coupled electron transfer (PCET) properties. 

Avena, M. J., L. E. Valenti, V. Pfaffen, and C. P. De Pauli. 2001. Methylene blue dimerization does not interfere in surface-area measurements of kaolinite and soils. Clays and Clay Minerals 49, no. 2 168-173. doi 10.1346/CCMN.2001.0490206. 

The Blue Dimer and Other Dinuclear Ruthenium Catalysts... 

THE BLUE DIMER AND OTHER DINUCLEAR RUTHENIUM CATALYSTS... 

Fig. 12 Frontier 3t (dRui-p -o-dRu2) molecular orbitals of the blue dimer.

The mechanism of catalytic water oxidation by the blue dimer was studied in detail by Baik at the DFT level. Unrestricted B3LYP calculations... 

Fig. 13 Energy profile, in kcal mol for the catalytic oxidation of water by the blue dimer. ISC, intersystem crossing.

Batista ER, Martin RL. Electron localization in the ground state of the ruthenium blue dimer. J Am Chem Soc. 2007 129 7224-7225. 

Ozkanlar A, Clark AE. Sensitivity of the properties of ruthenium blue dimer to method, basis set, and continuum model. J Chem Phys. 2012 136 204104. 

Bianco R, Hay J, Hynes JT. Theoretical study of 0-0 single hond formation in the oxidation of water by the ruthenium blue dimer. J Phys Chem A. 2011 115 8003-8016. 

Kuznetsov AE, Geletii YV, fEU CL, Morokuma J, Musaev DG. Dioxygen and water activation processes on mrJti-Ru-subsrituted polyoxometalates comparison with the blue-dimer water oxidation catalyst. J Am Chem Soc. 2009 131 6844-6854. 

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