Cobalt hexacyanoferrate in PAMAM doped silica matrix. 2. Structural and electronic characterization

Acomposite of silica sol–gel, generation-4 poly(amidoamine) dendrimer (PAMAM)and cobalt hexacyanoferrate (CoHCF)was synthesized as a potential electrochromic material. The solid-state voltammetry of the material had suggested that the two electroactive sites were present. To elucidate the redox properties, the electronic and the structure in the local atomic environment of Fe and Co was investigated by X-ray absorption spectroscopy (XAS). Although the nominal stoichiometries of the investigated CoHCFs were Co2 IIFeII(CN)6 (or K2CoIIFeII(CN)6) and KCoIIFeIII(CN)6, the spectral data demonstrated that CoIII was present in the composite. Among the supporting evidence for some metal-to-metal electronic transition of FeIII–CN–CoII to FeII–CN–CoIII was the shortening of the measured Co–N bond length in accord with the formation of CoIII. Further, IR measurements confirm the occurrence of charge transfer between Fe and Co sites in the silica–PAMAM composite.