Influence of different copper(II) salts on the oxidation and doping reactions of emeraldine base polyaniline

A spectroscopic investigation of the products formed in the reaction of emeraldine base (EB-PANI) with copper(II) ions in dimethylacetamide (DMA) is presented. It is well known that metal cations can dope emeraldine base polyaniline (EB-PANI) through a pseudo-protonation reaction. Resonance Raman, UV-vis-NIR, and EPR data, obtained for Cu2+/EB-PANI solutions prepared using CuCl2·2 H2O, Cu(NO3)2· 3 H2O or Cu(CH3COO)2·H2O as Cu2+ sources, showed that the species formed in reactions of EB-PANI and Cu2+ ions are dependent on the anions of the copper salt employed. EPR spectra pointed out that the environments of Cu2+ ions with acetate, chloride or nitrate as anions in DMA solution are distinct. Resonance Raman and UV-vis-NIR data demonstrated that the main reactions are the oxidation of EB-PANI to pernigraniline base (PB-PANI) and doping of EB-PANI to ES-PANI (emeraldine salt) when a direct coordination of Cu2+ ions to PANI exists. With nitrate as very weak coordinating anion, ES-PANI is formed preferentially. When copper chloride is used, both oxidation and doping of EB-PANI are verified. Conversely with acetate, the dimeric cage structure of this copper salt is preserved in solution, and oxidation of EB-PANI to PB-PANI is the only observed reaction. These results demonstrate the possibility of modulating the products of reaction between Cu2+ ions and EB-PANI in DMA solution by changing the counter ion of the Cu2+ source.