Complexation of polyaniline with Lewis acids - a Moessbauer spectroscopy study

Doping with Lewis acids is a new method for improving solution processibility of conductive polyaniline. We report here detailed Moessbauer spectroscopy studies of polyaniline complexed with Lewis acids containing Moessbauer active nuclei, namely SnCl4 and FeCl3. Films of Lewis acid doped polyaniline cast from nitromethane solutions show stoichiometries of PANI(MeCln)1(CH3NO2)1 (where n = 3 or 4, Me denotes Sn or Fe and PANI denotes one aniline repeat unit), 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. Moessbauer parameters of polyaniline doped with Sn Cl2 are consistent with hexacoordinated Sn(IV) in an environment of non-equivalent ligands. The spectrum of PANI doped with FeCl3 consists of two doublets with distinctly different Moessbauer parameters, which can be ascribed to two types of complexing sites (amine and imine nitrogens). From the temperature dependence of the isomer shift and the recoil free absorption, we have calculated the Moessbauer lattice temperature (THETA)m as probed by both complexing sites, which are 83 K for amine and 126 K for imine sites. (author)