Electronic spectra charge-transfer bands

The M(VI) oxidation state is represented in the 4d series by the hexafluorides, MFg, of the elements Mo, Tc, Ru, and Rh. All are obtained by direct fluorination of the metal and are unstable powerfully oxidising species — once again the instability seems most marked at the end of the series. Unfortunately hardly any electronic spectral data exist. The first charge-transfer band of the d°MoF(s has been located at 54 kK. (42), and a study of the vibrational spectrum of RuF6 (43) revealed electronic bands at 1.95 and 1.4 kK., which are probably the F2, r5 Ti, and /13,... 

As has been noted above, [Fe(HB(pz)3)2] undergoes a color change from deep violet to white upon heating, a change that is clearly revealed in its electronic absorption spectrum, see Fig. 4. The 297 K spectrum is dominated by a very intense charge-transfer band centered in the ultraviolet region and a less intense band centered at 19,000 cm-1. These absorptions account for... 

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... 

A number of tetracyanoethylene (TCNE) n complexes of mono-substituted [2.2]paracyclophanes were examined both spectroscopically and kinetically. The position of max of the longest-wavelength charge-transfer band in the UV spectrum of the complexes, and in some cases estimated equilibrium constants 76> were used as a measure of the relative 7t-base strengths of the substituted cycles 15>. From the results of this investigation it was at once clear that complexes of tetracyanoethylene and [2.2]paracyclophane with electron-releasing substituents (Type A,... 

Optical Absorption Spectra and Electronic Structure The optical spectra of all the doubledeckers are listed in Table I, On first glance, Ce(0EP)2 has a "normal" spectrum (7), However, the spectrum shows extra bands and therefore should be called "hyper", A small band appears at 467 nm (maybe a ligand-to-metal charge transfer band), and broad features extend far into the near infrared (NIR), The latter absorption may be due to exciton interactions. Contrary to the known rare earth monoporphyrins (7), it has been shown for the closely related cerium(IV)... 

While the band position in the spectra of acylmetallocenes is close to that of the parent, above 325 m its intensity is enhanced with the introduction of the —COR. (This is in contrast to the alkylmetallocenes, whose spectra are almost identical to the parent metallocene.) Below 300 m(x, however, the intense, broad end-absorption in the spectrum of the parent metallocene is replaced by two intense peaks (for acylferrocenes these appear near 230 and 270 m j.). These are believed to be associated in part with electronic transitions of the substituent with the ring, superimposed upon metal to ring charge-transfer bands.7... 

The electronic absorption spectrum of nickelocene has been recorded and analyzed in considerable detail by Scott and Becker.11 They found band maxima at 1920, 3075, and 6920 A and shoulders at 2700, 3450, 4400, and 5700 A. The band at 1920 A is believed to be an allowed transition which is designated as a W-F transition in ferrocene, but the intensity of this band is less than the N-V band in ferrocene. The shoulder at 2700 A is denoted as a N-Vor N-Q transition similar to the 2300 and 2600 A shoulders in ferrocene. The band at 3075 A is relatively intense and occurs at approximately the same wavelength as the intermolecular charge transfer band of ferrocene in carbon tetrachloride described by Brand and Snedden. The absorption spectrum of nickelocene in carbon tetrachloride shows no new bands other than those found in cyclohexane or ethanol. 

The combination of two redox reagents in the roles of donor and acceptor normally results in the formation of a charge transfer complex where the crystal structure of planar molecules show stacks of alternating donor and acceptor molecules (Figure la). The interplanar spacing between the molecules is usually shorter than the accepted norm of about 400 pm, a result interpreted as due to electronic interaction in agreement with the appearance of charge transfer bands in the absorption spectrum. 

The tetracyanonickelate(II) ion is the most extensively studied square planar complex of nickel(II). TTie electronic spectrum is characterized by d-d bands at 31 000-32 000 cm-1 (eM 500-800) and charge transfer bands (eM = 6000-15 000) at 33 000-37 000 cm-1. In Figure 22 the electronic and MCD spectra of K2Ni(CN)4 are shown. In the MCD spectrum of the low energy band (d-d), since C terms are zero because the ground state is lAlg, the presence of the... 

In the extreme class III behaviour,360-362 two types of structures were envisaged clusters and infinite lattices (Table 17). The latter, class IIIB behaviour, has been known for a number of years in the nonstoichiometric sulfides of copper (see ref. 10, p. 1142), and particularly in the double layer structure of K[Cu4S3],382 which exhibits the electrical conductivity and the reflectivity typical of a metal. The former, class IIIA behaviour, was looked for in the polynuclear clusters of copper(I) Cu gX, species, especially where X = sulfur, but no mixed valence copper(I)/(II) clusters with class IIIA behaviour have been identified to date. Mixed valence copper(I)/(II) complexes of class II behaviour (Table 17) have properties intermediate between those of class I and class III. The local copper(I)/(II) stereochemistry is well defined and the same for all Cu atoms present, and the single odd electron is associated with both Cu atoms, i.e. delocalized between them, but will have a normal spin-only magnetic moment. The complexes will be semiconductors and the d-d spectra of the odd electron will involve a near normal copper(II)-type spectrum (see Section 53.4.4.5), but in addition a unique band may be observed associated with an intervalence CuVCu11 charge transfer band (IVTC) (Table 19). While these requirements are fairly clear,360,362 their realization for specific systems is not so clearly established. 

It has been noted by Potasek [105] that electron tunneling in the donor-acceptor pair D-A may lead to the appearance of a charge transfer band in the absorption spectrum of this pair. The author obtained the following formula describing the dependence of the extinction coefficient, , of this band on the energy, E, of the absorbed light quantum... 

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