Os polypyridyl complexes

Run(Hedta)(NO+)]° and [Fen(Hedta)(NO )] have been shown to be effective electrocatalysts for the reduction of N02 in acidic aqueous media, to yield N20, N2, NH3OH+, or NH4 339,340 An element of selectivity is available by control of pH and applied potential. Steps involved in the typical six-electron reduction of nitrite to ammonia catalyzed by [Run(Hedta)(NO+)]° are summarized in Equations (67)-(69). The mechanisms by which nitrite is reduced appeared to be similar to those identified for Fe-porphyrin331 and Ru or Os-polypyridyl complexes.337... 

While the above-described instrumentation is an excellent choice for long-lived excited states such as the Ru " and Os polypyridyl complexes, organic-based chromophores and fluorescence labels frequently used by supramolecular chemists require higher time resolution. Commercially available time-correlated single photon counting (TCSPC) instruments can readily access... 

In the excited state quenching of a number of Ru- and Os-polypyridyl complexes by methyl viologen, the cage escape yield for MV+- radical varies only slightly, ranging from 0.14 to 0.27 ... 

Of the Ru(IV) complexes recorded here most are mono-oxo species which, despite the strong axial distortion brought about by the terminal oxo ligand, are probably all paramagnetic. Semi-empirical molecular orbital calculations (INDO/1) for epoxidations effected by oxo-Ru(IV) complexes have been reported (a non-concerted [1 h- 2] pathway was preferred) [642], [643] and for alcohol oxidations by octahedral species containing an Ru" (0) unit [644]. The reactivity of high oxidation-state polypyridyl complexes of osmium and Ru, with particular emphasis on Ru(IV) and Os(IV) oxo species, has been reviewed [43]. 

Orellana G, Garcia-Fresnadillo D (2004) Environmental and industrial optosens-ing with tailored luminescent Ru(II) polypyridyl complexes. In Narayanaswamy R, Wolfbeis OS (eds) Optical sensors industrial, enviromental and diagnostic applications. Springer series on chemical sensors and biosensors vol 1. Springer, Berlin Heidelberg New York, p 309-357... 

The coordination compounds are widely used as luminescent probes for polymer-based PSP. The coordination compounds are classified into two categories. One is the transition metal polypyridyl complex. In this group, transition metals are Ru2+, Os+ and Ir3+ as shown in Fig. 10. The second group comprises the metalloporphyrins as shown in Fig. 11. Pt2+ and Pd2+ porphyrins are especially used as PSP probes. 

Fleming CN, Maxwell KA, DeSimone JM, Meyer TJ, Papanikolas JM. Ultrafast excited-state energy migration dynamics in an efficient light-harvesting antenna polymer based on Ru(II) and Os(II) polypyridyl complexes. J Am Chem Soc 2001 123 10336-47. 

Chirality effects are also reported in the energy transfer from the ruthen-ium(II) polypyridyl complex to the osmium(II) complex in Langumuir-Blodgett (LB) films [76]. In this experiment, the LB film was prepared with [Ru(dp-phen)3]2+ (dp-phen = 4,7-dipheny 1-1,10-phenanthroline) and stearic acid, where the molar ratio was 1 1 to 1 4. The quenching reaction of the ruthenium(II) complex was carried out with optically pure osmium(II) complex, [Os(dp-phen)3]2+. This reaction consists of photoexcitation of the ruthenium(II) and osmium(II) complexes [Eqs. (29) and (30)], spontaneous decays of the excited ruthenium(H) and osmium(II) complexes [Eqs. (32) and (33)], and the energy transfer between the exited ruthenium(II) complex and the osmium(II) complex [Eq. (31)]. 

An unusual sequence of multielectron chemistry unique to Os (and Ru) is the reversible interconversion of NH3 and NO in polypyridyl complexes 67... 

Ward and coworlters extensively studied energy transfer between metal polypyridyl complexes preorganized via complementary Watson-Crick base pairing. Ensemble 9 has an association constant of 5 x 10 in CD2CI2, and the /cen for the Ru Os energy transfer... 

The charge was introduced through oxidation of the excited polypyridyl complexes by an irreversible oxidant, 4-methoxybenzenediazonium tetrafluoroborate in acetonitrile solvent. Remarkably, the Ru excited states in the mixed-valent polymer were found not to be quenched by Ru or Os. This was attributed to the fact that these electron transfer reactions lie in the inverted region. This behavior differs from that found in homogeneous aqueous solution where excited state quenching is near diffusion controlled. Possibly the relative immobilization of the reactants on the polymer, along with the smaller value for Aout in acetonitrile, prevents their reaction at the separations and orientations at which electron transfer occurs in homogeneous solution. 

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