Lewis Acid Doped Polyaniline:  Preparation and Spectroscopic Characterization

It is demonstrated that polyaniline can be solubilized in nitromethane via complexation with SnCl4. The solutions of PANI−SnCl4 complex show UV−vis−NIR spectral features distinctly different from those reported for Brönsted acid doped PANI. The removal of the solvent results in the formation of a free-standing film of SnCl4-doped PANI. The solid-state complex shows the stoichiometry of PANI(SnCl4)1.0(CH3NO2)1.0, which means that both types of polyaniline nitrogens (imine and amine) participate in the complexation reaction and one solvent molecule is introduced in the polymer matrix per one Lewis acid molecule. Mössbauer parameters of the complex (IS = 0.43 mm/s vs SnO2, QS = 0.49 mm/s) are consistent with hexacoordinated Sn(IV) in an environment of nonequivalent ligands. XPS studies are in good agreement with Mössbauer spectroscopy, giving Sn3d XP spectra characteristic of SnCl4·2L complexes. Similar complexation can be achieved in dried PANI(HCl)0.5; however, in this case, SnCl4 is complexed only on nonprotonated nitrogen sites.