Spectroscopic studies of the reaction of iodine with 2,3-diaminopyridine

The charge-transfer interaction of 2,3-diaminopyridine (DAPY) and iodine has been investigated spectrophotometrically in the solvents chloroform and dichloromethane at room temperature. The results indicate the formation of 1:2 charge-transfer complex in each solvent with the observation of the two characteristic absorptions for triiodide ion around 355 and 295 nm. The iodine complex is formulated as (DAPY)I]+.I3-. The formation of the triiodide ion, I3-, is further confirmed by the observation of the characteristic bands for non-linear I3- ion with C2v symmetry at 151 and 132 cm(-1) assigned to nu(as)(I-I) and nu(s)(I-I) of the I-I bonds and at 61 cm(-1) due to bending delta(I3-). The mid infrared spectra of (DAPY) and triiodide complex are also obtained and assigned.