Rhodium complexes excited state

Polypyridine rhodium(III) complexes (RM ) may be reduced by one-electron reductants The reductants which have been successfully employed include Ru(bpy)32+, the luminescent charge-transfer excited state of Ru(bpy)32+ (J, 9)... 

Skibsted LH. Photoisomerization of rhodium amine complexes. The deduction of an excited state reaction mechanism. Coord Chem Rev 1989 94 151-79. 

While not yet as extensive as the chemistry reported for bipy and phen complexes of ruthenium, the chemistry of rhodium polypyridine complexes (especially their excited states) has generated much recent interest. The claim of Lehn and co-workers805 that excited states of [Rh(bipy)3]3+ are involved in the photoinduced generation of H2(g) from water has sparked renewed efforts to understand the rich excited state chemistry of these complexes. 

Watts and coworkers reported the luminescence properties of cyclometalated iridium(III) and rhodium(III) complexes (see Cyclometalation). The dichloro-bridged dimers [M2(N C)4Cl2] (M = Ir, Rh HN C = Hppy, Hbzq) displayed intense emission with structural features in EtOH/MeOH/CH2Cl2 (4 1 1 v v) glass at 77 K. The emission of the rhodium(III) dimers was assigned to an lE excited state... 

Although the models have proved to be useful tools for rationalizing some aspects of the photosubstitutional behavior of simple transition metal complexes, they are not without deficiencies. For example, the predictions of reactivity made with the models are only qualitative. Thus a reaction that is predicted for a particular complex may not occur at all. Another important deficiency of the models was recently discussed by Ford (50). In the series of analogous rhodium(III) j omplexes, Rh(NH3)5X"" (X = NH3, H2O, 0H , Cl, Br, and I"), relative quantum yields of ligand substitution are strongly dependent on the rates of physical radiationless decay of the excited complexes to the ground state species. According to the Zink model, however, relative quantum yields within such a series should reflect "reactivities" of the excited state complexes (44,47). 

Brensted Base Quenching. The trans-Rh(cyclam)(CN)2+ ion (cyclam = 1,4,8,11-tetraazacyclotetradecane) displays luminescence from a ligand field excited state (3LF ) at room temperature, in an aqueous solution with a lifetime (8.1 /is) [53] several orders of magnitude longer than generally observed for rhodium(III) amine complexes [54]. As was observed for some other Rh(III) amines, the 3LF emission from trans-Rh(cyclam)(CN)2 is quenched by OH- in solution (Eq. (13)), a process attributed to amine deprotonation [55],... 

Thus the activation volume AV for the rate constant kp of an individual ES reaction pathway can be evaluated if the pressure dependencies of the photoreaction quantum yield, of intersystem crossing and of the ES lifetime can be separately determined. However, such parameterization becomes considerably more complex if several different excited states are involved or if a fraction of the photosubstitution products are formed from states that are not vibrationally relaxed with respect to the medium. Currently, parameterization of pressure effects on photosubstitutions has been attempted for a limited number of metal complexes. These include certain rhodium(III) and chromium(III) amine complexes and some Group VI metal carbonyls, which will be summarized here. 

Rhodium(lll) complexes Collaborative studies between van Eldik, Ford and coworkers have led to thorough parameterization of pressure effects on photosolvolysis of the rhodium(III) halopentaammines Rh(NH3)sX + (Eq. 6.18) [39-45]. For these systems LF excitation is followed by rapid intersystem crossing (cDisc 1) to the lowest energy LF state E from which reactive (kp), radiative (k,) and non-radiative (k ) deactivation occur competitively (Fig. 6.10) [41, 46]. Rate constants for individual excited state processes were calculated from phosphorescence quantum yields fl>r, lifetimes r and quantum yields for halide ([Pg.198]

A report has appeared of the results of energy-transfer and electron-transfer quenching experiments involving the A2 excited state of some binuclear rhodium isocyanide complexes, e.g. [Rh2(br)4], where br = 1,3-di-isocyanopropane, and [Rh2(TMB)4] , and TMB = 2,5-dimethyl-2,5-di-isocyanohexane. Detailed... 

Chemical or photochemical oxidation of a nucleic acid is accomplished very efficiently by a variety of metal complexes. In the presence of hydrogen peroxide and thiol, bis(phenanthroline) cuprous ion very efficiently cleaves DNA (26). Tris(phenanthroline) complexes of cobalt(IIl) or rhodium(III) promote redox reactions in their excited states (27, 28). These photoac-tivated probes bind to the DNA helix in a fashion comparable to the spectroscopic probes described above and then, upon photoactivation, promote DNA strand cleavage. 

In contrast to common luminescent rhodium (III) systems, the complexes [Rh(ppy)2(TAP)]+ (36) and [Rh(ppy)2(HAT)]+ (37) showed structureless emission spectra in fluid solutions at room temperature and in rigid glass at 77 K. In addition to the observation of the irreversible oxidation wave, the emission was assigned to an SBLCT (cr(Rh-C) — 7t (TAP or HAT)) excited state. The iridium(III) complex [Ir(ppy)2(HAT)] + displayed dual emissions in 77 K glass, which was assigned to excited states of MLCT An (Ir) — ... 

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