The infrared spectra of complexes of CF3I and CF3Br with trimethylamine, reported in Part III, are considered in detail. The spectra are compared with those of related complexes. Considerable regularities are found. It is suggested that published assignments to δa1(Nme3) and δE(Nme3) in certain trimethylamine complexes should be reversed. The intensity of δA1(Nme3) is considerably greater in its complexes with CF3I and CF3Br than in the free base: an explanation in terms of variation of the extent of electron transfer with vibrational coordinate is suggested. Force constants of the complex are calculated for several simplified models of the complex and possible errors are considered in some detail. The N-I bond stretching force constant in the complex CF3I.N(CH3)3 for the room temperature gaseous, solution in carbon tetrachloride, and liquid phases and 80 K solid phase are respectively 0.19 ± 0.05, 0.29 ± 0.03, 0.31 ± 0.03 and 0.53 ± 0.09 mdyn/Ǻ. Corresponding values for the C-I stretching force constant in the complex and (in parenthesis) values for free CF3I are: 2.14 ± 0.04(2.44 ± 0.02); 2.02 ± 0.03(2.42 ± 0.02); 2.00 ± 0.03 (2.42 assumed); 1.85 ± 0.04 (2.32 ± 0.02). For CF3Br.N(CH3), (solid) N-Br and C-Br force constants are 0.29 ± 0.05, 2.59 ± 0.05 (3.15 ± 0.02). Less definite information was obtained about the other force constants of the complex. The trimethylamine C-N stretching force constant decreases on formation of the complex; the decrease is greatest for solid CF3I.N(CH,3),. Potential energy dis- tributions are calculated. Possible causes of the changes of the A1 and E CF3 stretching frequencies on formation of the complexes are considered; several factors appear to be involved.

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.

Equimolar liquid mixtures of CF3I, C2F5I or C3F7I and NMe3, Net3 or NPr3 were examined by infrared, far-infrared and N.M.R. spectroscopy. In the liquid mixtures of the halides with NMe3 or Net3 a broad absorption band at respectively c. 100 cm-l or c.75 cm-1 was observed, which is assigned to the N-I stretching mode of the intermolecular complex, analogous to the complexes described in Parts 111 and IV. The fluorine resonances in CF3I and in the ?CF3I groups are shifted markedly upfield in the equimolar liquid mixture compared to the liquid halide. Upfield shifts caused by the amines are in the order NMe3 > Net3 > NPr3. Infrared frequency shifts suggest that NMe3 forms stronger complexes with these halides than does NEt3.

Twelve of the bands observed in the infrared and Raman spectra of the anions, O-methylmonothiocarbonate and 0-methyldithiocarbonate, have been assigned to in-plane vibrations, on the basis of normal coordinate analyses. It is shown that, because of the large number of parameters, vibrational studies of this type cannot be used to determine, unambiguously, the relative contribution of the canonical forms -S(-O)C=O+-CH3 and 2-S2C=0+-CH3 to the structures of the corresponding anions.