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

Abstract 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 Cu 2+ /EB-PANI solutions prepared using CuCl 2 ·2 H 2 O, Cu(NO 3 ) 2 · 3 H 2 O or Cu(CH 3 COO) 2 ·H 2 O as Cu 2+ sources, showed that the species formed in reactions of EB-PANI and Cu 2+ ions are dependent on the anions of the copper salt employed. EPR spectra pointed out that the environments of Cu 2+ 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 Cu 2+ 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 Cu 2+ ions and EB-PANI in DMA solution by changing the counter ion of the Cu 2+ source.