Charge-transfer absorption band characteristics

Me2-4,4 -bipy ) have been used to evaluate the rate constant for inter-molecular reaction transfer within the ion pair. Use of a thermochemical cycle has provided a value for the rate of the overall reaction [Fe(CN)6] + PQ " (k2 0.2 X 10" M s ), which compares well with Marcus theory predictions. It is suggested that data on electron transfer processes may be derived from analysis of charge transfer absorption band characteristics. 

The addition of small amounts of inert salts such as tetrabutylammo-nium perchlorate (TBAP) or hexafluorophosphate (TBAH) to solutions of charge-transfer salts induces large changes in the intensity of the charge-transfer absorption bands. The magnitude of the salt effect is most pronounced in nonpolar solvents (THF, CH2C12). The monotonic decrease in the CT absorbance with increasing amounts of added TBAP is characteristic of the facile competition for the contact ion pair (42), namely,... 

The existence of the charge-transfer absorption bands is characteristic of important electron donor-acceptor contributions to the contact ion pair that is the direct precursor in the formation of metal-metal dimers by the mutual annihilation of carbonylcobalt(I) cations and carbonylcobal-tate(—I) anions (79). The diverse results cannot be explained by any single process in which the metal-metal bond for the dimer is formed by the... 

The Z value was defined by Kosower as the energy of electronic transition corresponding to the charge-transfer absorption band of l-ethyl-4-carbo-methoxy pyridinium iodide, a substance which has an ultraviolet spectrum remarkably sensitive to solvent polarity. Application of this method involves the determination of the spectral characteristics of the solubilizate in a number of solvents of known Z values and the establishment of a relationship between Z values and the energy of transition which is readily obtained from the wavelength of maximum absorbance. From this relationship the Z value of the micellar micro-environment may be determined from the wavelength of maximum absorbance of the solubilizate when solubilized within the micelle. Utilizing this... 

The demetalation process was followed by absorption spectrophotometry (measurement of the decay, as a function of time and cyanide concentration, of the di-copper(I) complexes characteristic metal-to-ligand-charge-transfer (MLCT) bands in the visible region [111]) which gave access to the kinetic parameters, in particular to the second-order dissociation rate constants CN given in Table 1. 

Of particular interest is the effect that air exposure has on the Cp2Fe/NaY sample, as illustrated in Figures 14C, D the ferrocene is slowly oxidized (whether it is oxygen or water or both is still under investigation) to the ferricenium cation as reflected by the drop in intensity of the 440 nm ferrocene band and the concomitant growth of the characteristic 617 nm charge transfer absorption of Cp2 Fe+. 

The absorption spectrum of the Field-Durrant solution with potassium bicarbonate is characteristic of the cobalt(III) complex there are two d—d absorption bands and one charge-transfer (CT) band, and the pattern of the spectrum is similar to that of the familiar tris(oxalato)cobaltate(III) anion except for some bathochromic shifts of the carbonate complex. Regarding the d—d bands, conformity to Beer s law is confirmed with ca. 10 10 mol/dm solutions using 1-cm absorption cell. Data on the solution spectrum with the values of the parameters A and B are given in Table 2.1... 

Nagy et al [Na 72, Na 74, Du 75] classified organic solvents into groups on the basis of the solvent dependence of the absorption bands characteristic of the charge-transfer complexes of substituted phthalic anhydrides with substituted naphthenes, naphthalenes and anthracenes, and examined possible correlations between this grouping and other solvent parameters. 

The absorption spectra of the ligands 1 and 2 exhibit the characteristic bpy bands in the UV region. In all the complexes studied the ligand centered (LC) bands in the UV region are accompanied by the characteristic [12,13] metal-to-ligand charge transfer (MLCT) bands in the visible (Table I). For illustration purposes, the visible spectra of 1.RUg, 1-OSg, and I.RUgOs are displayed in Fig. 3. 

Figure 5a shows the electronic absorption spectrum at -173 °C, which is reminiscent of that of crystalline solid Coni(DBCat)(DBSQ)(bpy) (Pierpont, 2001). At low temperatures, an absorption band characteristic of a ligand to metal charge transfer (LMCT) from DBCat ligand to central cobalt was observed at around 610 nm. As the temperature increases from 7... 

In diaryl cyclopropenones, the UV data are not very characteristic and resemble those of diaryl cyclopropenones and stilbenes as well as diaryl cyclopropenium cations, as shown in Table 8. Recently a new long-wave absorption band was found164) in diphenyl cyclopropenone [362 nm, log e = 3.06 (cyclohexane)] which was assigned tentatively to an intramolecular charge-transfer. 

The triruthenium derivatives 31-35 show characteristic intracluster charge transfer (IC) absorptions in the visible to near-infrared region (600-1000 nm) and cluster-to-ligand charge transfer (CLCT) transitions at 320-450 nm. Compared with the low energy bands in [Ru3n m m]+ complexes 31-35, those in the one-electron reduced neutral [Ru3 ]° species are remarkably red-shifted. The decrease in energy for these transitions by one-electron reduction reflects a rise of the occupied d% levels as the number of electrons increases. Complexes 31-35 exhibit... 

Electronic spectra of metalloproteins find their origins in (i) internal ligand absorption bands, such as n->n electronic transitions in porphyrins (ii) transitions associated entirely with metal orbitals (d-d transitions) (iii) charge-transfer bands between the ligand and the metal, such as the S ->Fe(II) and S ->Cu(II) charge-transfer bands seen in the optical spectra of Fe-S proteins and blue copper proteins, respectively. Figure 6.3a presents the characteristic spectrum of cytochrome c, one of the electron-transport haemoproteins of the mitochondrial... 

---