LMCT bands

The effects of metal-to-metal electronic coupling are observed for several complexes where a ferrocene moiety is bound to transition-metal complexes with a -conjugated chain, 68 (167), 69 (168), and 70 (169). Tertiary amine-ferrocene conjugated molecules, 71, show two-step le oxidation, and their monocationic forms exhibit strong LMCT bands at 600-700 nm (170). 

Figure 15 shows the modification in the UV-visible spectra of TS-1, initially in vacuo, upon interaction with H20 (752). Evidence of the interaction of NH3, a stronger base, is also shown. The LMCT band (mentioned in Section II.A.3) undergoes a red shift of the edge as a result of the increase of the coordination sphere about Ti4+ ions. In Ti02, in which Ti is surrounded octahedrally by six O atoms in its first coordination sphere, the Ti4+02- — Ti3+0- LMCT is also red shifted to lower wavenumbers (32,000 cm-1). A stronger perturbation is obtained upon dosing of NH3, but the line shape of the UV-visible curve is... 

In an attempt to quantify the relationship between the TiOOH groups and the yield of propene oxide from the extinction coefficients of the latter s 1409-and 1493-cm-1 bands, it was determined that 0.6 mol of the epoxide formed per mole of framework Ti center in the molecular sieve. That is, at least 60% of all framework Ti (80% of the surface-exposed Ti) is converted to TiOOH upon reaction with H202. The consumption of the TiOOH species during the oxygen insertion into propene was also independently confirmed by the loss in intensity of its LMCT band at 360 nm when the catalyst was brought in contact with propene at room temperature (Fig. 50). 

Figure 10 shows that Ru + and Ni + can also be extracted into G4-OH dendrimers. For example, a [Ru(NH3)5Cl] + solution has an LMCT band at 327 nm ( 1200 cm ).However, after addition of G4-OH to this solution the LMCT... 

Figure 16 a shows UV-vis spectra of an aqueous Cu +/G6-OH solution before and after reduction. At pH 7.5 a strong LMCT band is evident at 300 nm (e 4000 cm 0, which (as discussed earlier) is not present in the absence of... 

The spectra of the complexes LmM"+l R, containing a metal-carbon -bond, usually consist of several distinguishable bands the major bands with high extinction coefficients in the UV region are LMCT bands, followed sometimes by bands with mixed characters and the d-d bands in the visible region with low extinction coefficients. The location of the maximum of the LMCT transition is naturally strongly affected by the nature of the substituents R and by the redox potential of the central M(ra + 1) ions. 

Both p-1,2 and p-p2 172 peroxo structures can account for the occurrence of two intense bands observed at 350 and 580 nm for oxy-Hc, because two distinct LMCT bands due to Of n and 07r are predicted to split significantly. Detailed theoretical analyses of the Of" — Cu(II) LMCT bands have been reported by Ross and Solomon (254). According to the analyses, the 7r -7r split in p-172 tj2 is larger than that of cis-p-1,2, suggesting that the p-172 172 structure is more likely as a model for oxy-Hc. The low 0-0 vibrational stretch of oxy-Hc was also interpreted in terms of the p-172 tj2 structure based on MO calculations (254), which indicated that Of o- can act as a 7r acid. Hence, the back-donation of the copper to weaken the 0-0 bond of the peroxide ion may result in an unusually low 0-0 frequency in the p-172 Tj2 peroxo complex. In contrast, no clear account was addressed for the low 0-0 frequency of oxy-Hc, assuming the cis-p-1,2 structure. 

Polyoxometallates (POMs), molecular anionic metal oxides, show the ability to act as homogeneous photocatalysts in electron transfer from organic electron donors to metal ions. In the process, illumination at the LMCT band (visible and near-UV regions) renders POMs strong oxidants that are able to abstract electrons from a... 

---