Mixed valence ruthenium complexes

Ruthenium mixed-valence complexes are ubiquitous in coordination chemistry. For this reason, the common oxidation states of ruthenium will be adopted in the following discussion of comproportionation constants. 

Mixed Ruthenium-tii) and -(m) Complexes.—Interactions of the oxo-centred RuI 1 acetate [Ru30(C02Me)6(Me0H)3]+ and the reduced species [Ru30(C02Me)6 (MeOH)3] with carbon monoxide, sulphur dioxide, and NO have been studied.71 Scheme 5 summarizes the products obtained from the latter mixed-valency complex following carbonylation. Only a monocarbonyl complex is seen to be formed, and the... 

There are several photocatalysts mimicking hydrogenase activity that are not based on metalloporphyrin systems. Among them there are mixed-valence complexes of rhodium or iridium, [41] as well as complex systems encompassing photosensitizers (eg ruthenium complexes) attached to a catalytic bimetallic centre [43], The design of more sophisticated systems approaches that of photosynthetic processes [44],... 

There have been only a handful of studies on exchange coupled ruthenium dimers and yet the information available on metal-metal coupling is potentially as valuable as that obtained from mixed-valence complexes. The reason for this lack of activity has been the greater familiarity of researchers with the chemistry of Ru(II) bound to 7r-acid ligands. The synthetic pathways to complexes of this type are well explored (7) and possess the tremendous advantages of stability and ease of handling. Ru(II) complexes that incorporate anionic n donor... 

In the simplest case of a donor-acceptor (D-A) molecule, the nonlinear optical activity arises from the electric-field-induced mixing of electronic states such as D-A and D+-A . This makes the response (polarizability) of the molecule different according to the sense of the electric field, and a second-order hyperpolarizability fi coefficient) is observed. If D and A are connected by some bridge, its role in promoting the electronic interaction will be quite similar to the bridge role in mixed-valence complexes. Metal complexes can play the role of donor or acceptor groups. Recent examples have been described with ferrocene or ruthenium(pentaammine) groups [48], but they are either monometallic or too short to be considered in this review. 

These ion movements are shown schematically in Figure 11. It should be noted that the orientation of the protonmotive force is reversed from that in vivo. The proton-pumping Mg -ATPase will be described in a later section. This calcium transport system is not inhibited significantly by ruthenium red, the classical inhibitor for calcium uptake in mitochondria. However, uptake of Ca by these inside-out vesicles of E. coli is inhibited dramatically by a dimeric, mixed-valence complex of Ru" ", [(NH3)3RuCl3Ru(NH3)3]. The mode of action remains to be established. 

Finally, the structural characteristics of the 1,8-naphthyridines favour their behavior as bidentate and dinucleating ligands, thus leading to short metal-metal separations in late transition-metal complexes,24"26 and to the stabilization of mixed-valence complexes.27,28 The dinuclear ruthenium complex [ Ru(napy)(H20)2 (/i-Cl)(/i-0H)](C104)2 is a stable and active catalyst for the oxidation of alcohols and the epoxidation of alkenes, while its mononuclear precursor is much less active.29... 

Electrochemical studies of the tetranuclear ruthenium complex of ligand (62) indicate two reversible two-electron redox waves in the anodic region attributed to oxidation of the Ru11 metal centers. This complex is said to act as two binuclear subunits with little or no electronic interaction between subunits. The first two-electron oxidation process results in a mixed valence complex with each subunit having a Ru11 and Ru111 metal center. 

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