Electronic, infrared, and Raman spectral studies of the reaction of iodine with 4-aminopyridine

The reaction of iodine as an electron acceptor with the base 4-aminopyridine (4APY) has been investigated spectrophotometrically in chloroform at room temperature. The electronic absorptions, infrared and Raman spectra, photometric titration as well as elemental analysis of the obtained iodine complex indicate the formation of the pentaiodide charge-transfer complex with the general formula [(4APY)2]+I5−. The characteristic strong absorptions of I5− are observed around 380 and 295 nm. Far infrared and Raman spectra of the solid complex show the vibrations of the linear I5− ion with D∞h symmetry at 154, 104 and 89 cm−1 assigned to νs(II), outer bonds, νs(II), inner bonds and νas(II) inner bonds, respectively.