Spectra of charge transfer complexes

Fig. 8.15 The relation between i cr of the spectra of charge-transfer complexes and the half-wave potentials of electron acceptors [53]. Electron acceptor derivatives of phthalic anhydride, quinone and nitrobenzene, and tetra-cyanobenzene and tetracyanoethylene.

Most of the information presently available has been obtained with a view to comparing selenophene and tellurophene with furan and thiophene, and has already been discussed in Chapter 3.01. The resulting ionization potentials are in good agreement with those deduced from the spectra of charge transfer complexes with tetracyanoethylene (82CS(20)214, 75JCS(F1)2045). 

In the structure 31 (X = Si) strong electron donation from the Si-C bond to cyclopropyl was proposed to occur based on the electronic spectra of charge transfer complexes and IR and Raman spectra and a similar interaction for the Sn analog was deduced from the UV photoelectron spectrum and proposed to involve the conformation indicated. Structural studies of these compounds to determine if these conformations are actually favored could be most informative, as would investigation of conformationally fixed compounds and detailed theoretical calculations. 

A number of papers have appeared which describe absorption spectra of charge-transfer complexes in solutions without however isolating the actual complexes. 

Familiar examples of charge-transfer complexes include the phenolic complex of iron(III), the 1,10-phenanthroline complex of iron(II), the iodide complex of molecular iodine, and the ferro/ferricyanide complex responsible for the color of Prussian blue. The red color of the iron(III)/thiocyanate complex is a further example of charge-transfer absorption. Absorption of a photon results in the transfer of an electron from the thiocyanate ion to an orbital that is largely associated with the iron(III) ion. The product is an excited species involving predominantly iron(ll) and the thiocyanate radical SCN. As with other types of electronic excitation, the electron in this complex ordinarily returns to its original state after a brief period. Occasionally, however, an excited complex may dissociate and produce photochemical oxidation/reduction products. Three spectra of charge-transfer complexes are shown in Figure 26-4. 

Figure ILL Schematic potential energy diagram for spectra of charge transfer complexes...

Sasaki K, Aida K (1980) IR-spectra of charge transfer complexes between ICl, IBr and aminopyridines. J Inorg Nucl Chem 42 13-15... 

Safin, D.K. and Chmutova, G.A. (1985) Solvation effects in complexation reactions, n. Sol-vatochromism and the nature of absorption bands in the electronic spectra of charge-transfer complexes between iodine and Group VIA element-containing organic compounds. Zh. Ob-shch. Khim., 55, 2564-2572. 

De Leeuw, J., Van Cauteren, M. and Zeegers-Huyskens, T. (1974) Infrared spectra of charge transfer complexes between iodine cyanide and p5nidine derivatives. I. Complexation constant and V I—C stretching vibration. Spectwsc. Lett., 7, 607-614. 

Ill. De Leeuw, J. and Zeegers-Huyskens, T. (1975) Vibrational spectra of charge transfer complexes of iodine cyanide. IB. Infrared spectra at low frequencies (200-50 cm ). Adv. Mol. Relaxation... 

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