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.