Vibrational Frequencies of Anions

One of the proofs that the complexes of aromatic hydrocarbons with halides of the third-group metals and with hydrogen halides are salts of the hypothetical acids HMY4 and HMjY is the detection of the bands of the anions (MY and MjYf) in the low-frequency region. 

The tetrahedral anions MY4 (AlCl, AlBti , GaClf, BF4T etc.) belong to the T4 group of symmetry and have four normal vibrations shown in Fig. 13 All these vibrations are active in the Raman spectra, the most intensive and the only polarized line being the one assigned to the Vj stretching vibration. 

39 The hydrogen bond with the hydroxy group hydrogen and different anions has been studied for O-protonated tropone and carbonyl derivatives of aromatic systems .  

The band of the V4 deformation is less accessible for observation in the IR and its evidence is scarce PCI4 — 180cm ( 2115)2011 — 179 cmRaman spectra of the AlCHf anion are listed in Table 40. An intensive polarized line Vi and a depolarized line of mean intensity of V4 are independent of the cation at 350 and 180 cm respectively the V3 stretching vibration correlates with a weak line at 490 cm. The line of the Vj symmetric deformational vibration is less stable it seems to be sensitive to ambient particles. 

Vibrational frequencies of AlBr4 in the spectra of various salts are summarized in Table 41. 

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