Electron transfer and spin transition in metal-hexacyanoferrates driven by anatase TiO2: electronic and structural order effects

Abstract

⁵⁷Fe Mössbauer spectroscopy was used to highlight a charge transfer mechanism in cobalt hexacyanoferrate (CoHCF) when synthetized in the presence of anatase TiO₂. The electron transfer in TiO₂–CoHCF composites along the Co–NC–Fe–CN–Co chain is confirmed by the unequivocal evolution of the typical quadrupole doublet of Fe(II) and Fe(III) in pristine CoHCF into the single line spectrum of the Fe(II) species when CoHCF is nanodispersed on TiO₂ anatase. Parallel galvanostatic measurements also confirm the electron transfer mechanism induced by TiO₂. To the best of our knowledge, this is one of the first examples of the triggering of spin-crossover phenomena in metal-hexacyanoferrate based-molecular solids by an external stimulus other than photoexcitation and most of all one of the first studies in which a completely pure low-spin Fe(II) is obtained starting from a mix of low-spin Fe(II) and Fe(III).