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Keywords:

Science & Technology, Physical Sciences, Chemistry, Physical, Chemistry

Abstract:

The frequency, intensity, and depolarization ratio of the νBr-Br Raman band of charge transfer complexes of bromine with several pyridine derivatives have been determined in dichloromethane solution at 296 K. The frequency shift ΔνBr-Br is linearly related to the pKa of the pyridines. Complex formation brings about an enhancement of the depolarization ratio and of the absolute intensities of the νBr-Br band. From these experimental data, the mean value ᾱR′ and the anisotropy derivatives γR′ of the Br-Br bond have been calculated and it is shown that complexation induces a greater increase of γR′ than of ᾱR′. Further, the parallel (αR′)∥ and perpendicular (αR′)⊥ components of the bond polarizability derivatives have been calculated; the (αR′)∥ values are seen to increase by a factor of 2 or more and are related to the weight of the dative structure; the (αR′)⊥ values become very low. These effects are discussed in terms of the variation of the Br-Br distance and of the vibronic effect. © 1978 American Chemical Society.