Creutz—Taube complex

H2 or O2 from water in the presence of a sacrificial reductant or oxidant employ a mthenium complex, typically [Ru(bipy)2], as the photon absorber (96,97). A series of mixed binuclear mthenium complexes having a variety of bridging ligands have been the subject of numerous studies into the nature of bimolecular electron-transfer reactions and have been extensively reviewed (99—102). The first example of this system, reported in 1969 (103), is the Creutz-Taube complex [35599-57-6] [Ru2(pyz)(NH3. 

A special representative of class IIIA is the Creutz-Taube complex [101]. This is a binuclear complex [(NHjlsRufpyrazinelRufNHj) ]. Various experimental results led to conflicting conclusions concerning its electronic structure. A combined attack [101] has shown, however, that we are not dealing with a... 

DR. SCHATZ I think those systems are not simpler. Since the intervalence band is at an order of magnitude lower energy than the intra-unit electronic transitions, one can use first-order perturbation theory in treating the former, but not the latter. I am assuming that other electronic states do not mix in significantly i.e., it is just 2,3 and 3,2 as the electronic basis in the Creutz-Taube complex, for example. If other electronic states mix in, the model is dead. 

In the six-membered diazine systems, (93 95), the most widely investigated ligand is pyrazine (93) in the model pyrazine bridged mixed valence compound (103) (see Mixed Valence Compounds and Creutz-Taube Complex). The coordination chemistry of the aliphatic analog, piperazine (98), is not well developed. 

The most intensively studied diazine is undoubtedly pyrazine (7), present in the so-called Creutz-Taube complex [(H3N)5Ru(pyrazine)Ru(NH3)5] , a well-known mixed-valence compound. Examples of other bridged compounds (11) are the chain compound Cu(N03)2 (pyrazine) and the two-dimensional C0CI2 (pyrazine) (see Figure 8). The synthesis of the corresponding Zn compormd probably proceeds via an intermediate which is immediately converted to the end-product via crystallization, resulting in a unique acoustic emission. ... 

One of the more femous species in coordination chemistry is the Creutz-Taube complex. 

The dimetallic complex with a pyrazine bridge is shown in Figure 10.7 and is referred to as the Creutz-Taube ion in the case when the total charge is -1-5. Another possible bridge, dipyridine, is shown in Figure 10.8. (NH3)5RuC4N2H4Ru(NH3) +, the Creutz-Taube complex, has very distinct spectral properties from the others, immediately suggesting delocalization. X is approximately equal to 1 eV. 

Carol Creutz confirmed (1983) the delocalization by changing the polarity of the solvent. In the localized complexes, the spectrum depends almost linearly on X. However, this is not the case for the Creutz-Taube complex. Thus, the charges in this bimetallic complex are delocalized, as has been found in a number of experiments. A number of additional experiments to find out if the Creutz-Taube ion is really delocalized have been carried out. Reymers and Hush have discussed these experiments with the conclusion that the Creutz-Taube ion is, in fact, delocalized. This means that the oxidation states of Ru atoms are the same and equal to -t-2.5. 

In this example, the formation of the chloride bridge was not observed experimentally but was inferred from the analysis of the product analysis. The Creutz—Taube complex, shown in Figure 6, is a model for the bridged intermediate. This ion was named after Carol Creutz, who prepared it while working with Taube. Pyrazine is the bridging Hgand here. In the Creutz—Taube ion, the average oxidation state of Ru is +2.5. Spectroscopic studies have shown that the two Ruthenium centres are equivalent, which indicates the ease with which the electron hole communicates between the two metals. Many more complex mixed valence species are known both as molecules and polymeric materials. 

Day pointed out in a recent review, that the very existence of such a conflict of evidence means that the Creutz-Taube complex lies very near to the borderline between classes II and III, and is thus very far from being a typical case / ... 

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