The vibrational spectra and structure of the bis(pyridine)iodine(I), bis(pyridine)bromine(I), bis(γ-picoline)iodine-(I) and bis(γ-picollne)bromine(I) cations

ir (80–4000 cm−1) and Raman spectra of various perchlorate, tetrafluoroborate, and hexafluorophosphate salts of bis(pyridine)iodine(I), bis(pyridine)-bromine(I), bis(γ-picoline)iodine(I) and bis(γ-picoline)bromine(I) have been examined in various media. For the first three cations, the spectra are sufficient to establish the linearity of the N-I-N and N-Br-N groups, and the presence of a centre of symmetry, in both mull and solution. In the iodine cations the mull spectra indicate coplanarity of the two ligand rings, and there is slight evidence that this persists in solution. Shifts of sensitive ring modes indicate the charge distribution, which is compared with the corresponding charge-transfer complexes. In contrast to the charge-transfer complexes, solvent effects are slight.