In nonpolar solvents, iodine interacts with pyridine to form a stable molecular complex Pyr*I-2. In binary mixtures, and more generally in polar solvents, the I-2/pyridine complex dissociates to form ionic species. Two different ionization mechanisms are proposed. It has been found that (1) the first reaction, fast (characteristic time ranging from picoseconds to nanoseconds), is reversible and favored by an increase of the polarity of the medium and/or a decrease in temperature and (2) the second process, which reaches equilibrium very slowly (few days), is irreversible and favored by an increase of the donor strength and/or of the temperature.