Donor-acceptor complexes formed by perfluoro-organo bromides and iodides with nitrogenous and other bases. III. Qualitative examination of condensed phase spectra of CF₃I and CF₃Br and of their complexes with trimethylamine and other bases

Abstract

This paper reports the spectra of (i) CF₃I, CF₃Br and N(CH₃)₃ as solutions in carbon tetrachloride at room temperature, as liquids at lowered temperatures and as solid films at 80 K and (ii) equimolar solutions of CF₃I and N(CH₃)₃ in carbon tetrachloride at room temperature, equimolar liquid mixtures of CF₃I and N(CH₃)₃ at both room and lowered temperatures and annealed solid films at 80 K of CF₃I-N(CH₃)₃ and CF₃Br-N(CH₃)₃. The spectra clearly show the existence of complexes to which, on the bases of evidence reported in Part I, we assign the structures CF₃I.N(CH₃), and CF₃Br.N(CH₃),. Differences between the spectra of the complexes and the spectra of the free components for the same phase include (a) the appearance in the spectrum of the complex of a low frequency band which we attribute to the N-I or N-Br stretching mode, (b) a strong band at a lower frequency than the carbon-halogen stretching mode in CF₃I or CF₃Br which we assign to the modified carbon-halogen stretching mode in the complex, much enhanced in intensity, (c) an increased frequency of the symmetric carbon fluorine stretching mode and a decreased frequency of the degener- ate carbon-fluorine stretching mode in the complex compared with the free components, (d) increase in intensity and frequency of v₇ (CNC symmetric bend) of trimethylamine, (e) doubling of several C-H stretching frequencies. The dependence on phase of the magnitudes of the differences in frequencies of corresponding modes in the complex and free components are solid (80 K) > liquid ≈ solution in CCI₄ > vapour phase. Some details of complexes of CF₃I and CF₃Br with some other electron donors are reported briefly.