Chemical Environment of Copper Aggregates Embedded in Polypyrrole Films: The Nature of the Copper−Polypyrrole Interaction

We report on the structural and electronic properties of copper aggregates embedded in composite polypyrrole films studied by X-ray absorption techniques (XAS). Measurements at the Cu K edge during in situ reduction suggest that the reaction starts with the formation of the complex [−[(C4H2N)3CH3(CH2)11OSO3-]yCu2+]n (y = 4), in which the copper is bonded to oxygen atoms. The reduction of this complex leads to the synthesis of Cu metal aggregates in the film. Measurements at the N K edge evidence that the incorporation of the metal in the polymer network does not disturb the electronic structure nor the environment of the nitrogen from the pyrrole unit. Measurements at the O K edge indicate that the metal/polymer interaction happens via hybridization of O 2p and Cu 3d orbitals, resulting in an enlace that has a quasi-covalent character. Scanning electron microscopy measurements show that dendritic-like copper aggregates are formed on the film surface.