New nickel(II) bis(salicylideneiminate) complexes with carboxyethylene linker connecting imine groups were obtained. Polymer films based on these complexes were synthesized by electrochemical polymerization. When studying ionic transport in polymer films using cyclic voltammetry and microgravimetry, it was found that during oxidation, polymers pass into a self-doped state, in which a positive charge on the polymer chain is compensated by a negative charge of the carboxyl group, and a cation, forming an ionic pair with this group in neutral polymer form, leaves the film.