Spectroscopic study of some tetrabromomethane complexes

Abstract

Results are presented from an investigation of the Raman and ultraviolet spectra of CBr4 in solutions containing benzene and from an ultraviolet investigation of the tetrahydrofuran-CBr4 system. The changes occurring in the ultraviolet spectrum for these systems have been analyzed quantitatively to determine the formation constants for one-to-one donor-CBrd complexes. Relative Raman intensity values are presented for three of the four CBr4 fundamentals in benzene-CBr4 solutions. These data were analyzed and interpreted in terms of complex formation, and the formation constants from this analysis were compared to those from the ultraviolet study. The two sets of formations constants agree, leading to the conclusion that formation of the same chemical species causes the observed changes in both the ultraviolet and the Raman spectra of CBr4 in benzene. The changes in the Raman intensities for CBr4 in solution with benzene are analyzed in terms of changes in the bond polarizability parameters, with results similar to those found earlier for solutions of Cc4 in donor solvents. The nature of the benzene-CBr4 interaction is discussed, and it is concluded that it is probably primarily electrostatic.The values of quantum yields of production of Fe(II), GFe(II), are about an order of magnitude lower in the microcrystalline solid compared with solution values, ranging between about 0.07 and 0.17 and increasing with increasing intensity and with decreasing wavelength. Values of GCo(I1) in the microcrystalline solid vary between about 0.07 and 0.55, are somewhat less than values for solutions, and are independent of intensity, but decrease with increasing exposure at the shorter wavelengths. It is suggested that hole-electron pairs are generated within the crystals; these subsequently generate radical ions at the surface.

Raman study of iodine complexes in solutions

“…We then considered only the relative scattering cross section of the I2 line with respect to the CC14 line. We found experimentally that in the absence of I2, the scattering intensity of the 217 cm -1 CC14 line is proportional to the concentration of CC14 in agreement with the results of Bahnick and Person [15]. Therefore, within experimental error, the scattering cross section of the CC14 line should be unaffected by the CC14-benzene interaction.…”

“…Unfortunately, there is inherent inaccuracy in the measurements of integrated intensity. The same difficulty clearly exists also in the measurements of Bahnick and Person [15]. In our case the accuracy is worse since the CC14 line overlaps slightly with the 12 line.…”

“…For complexes in solution, the variation of the Raman scattering cross section I2 should have the same functional dependence on the donor concentration as the extinction coefficient for charge-transfer absorption [15]. Thus, measurements of Raman scattering intensity of I2 as a function of the donor concentration should provide another test on the theories of complexes in solution.…”

“…Thus, measurements of Raman scattering intensity of I2 as a function of the donor concentration should provide another test on the theories of complexes in solution. Bahnick and Person [15] have in fact made such measurements on several charge-transfer complexes. The equilibrium constants deduced from their resuks by assuming 1 : 1 complexes agree with those obtained from ultra-violet measurements.…”

“…There have been several reports of infra-red [13] and Raman [14,15] experiments on charge-transfer complexes. Raman measurements on I2 complexes [14], 34 H. Rosen et al…”