Fe57Mössbauer spectroscopy studies of the conducting poly (p-phenylene)-ferric chloride system

Mössbauer-effect measurements have been used to characterize the conducting polymer obtained by the oxidation of poly ($p$-phenylene) [$p-{\left({\mathrm{C}}_6{\mathrm{H}}_4\right)}_x$] with Fe${\mathrm{Cl}}_3$. The ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer spectra show the existence of two distinctly different iron sites with Mössbauer parameters characteristic of ${\mathrm{Fe}}^{3+}$. The isomer shift and $\Delta E$ values of the principal site are within the range typically observed for Fe${\mathrm{Cl}}_4^{-}$ (${\delta }_{\mathrm{IS}}=0.30\mathrm{}$ mm ${\mathrm{s}}^{-1\mathrm{}}$, $\Delta E=0.35\mathrm{}$ mm ${\mathrm{s}}^{-1\mathrm{}}$). In the case of the second iron site, higher ${\delta }_{\mathrm{IS}}$ and $\Delta E$ values are observed: ${\delta }_{\mathrm{IS}}=0.4\mathrm{}$ mm ${\mathrm{s}}^{-1\mathrm{}}$, $\Delta E=1.10\mathrm{}$ mm ${\mathrm{s}}^{-1\mathrm{}}$. Significant line broadening of the second site as compared with the linewidth of the principal one is indicative of a ${\delta }_{\mathrm{IS}}$ and/or $\Delta E$ distribution. From the temperature dependence of the absorption area of the principal site, the Mössbauer lattice temperature ${\Theta }_M^{\prime }$ has been calculated in the framework of the Debye model in the high-temperature limit and within the thin-absorber approximation. The value obtained, ${\Theta }_M^{\prime }=88\mathrm{}$ K, is low and suggests a very loose bonding between the inserted anions and the host polymer.