Study on the spin crossover transition and glass transition for Fe(II) complex film, [Fe(II)(H-triazole) ₃ ]@Nafion, by means of Mössbauer spectroscopy

Abstract

[Fe(II)(H-trz)₃]@Nafion (trz = triazole) is a transparent spin crossover complex film, where the spin crossover transition between the low-spin (S = 0) and the high-spin (S = 2) states takes place between 225 K and 300 K. In this film, two doublets corresponding to the low-spin and high-spin states were observed in the ⁵⁷Fe Mössbauer spectra, reflecting the spin crossover transition. From the analysis of ⁵⁷Fe Mössbauer spectra, the Debye temperatures of the low-spin and high-spin sites were estimated at 185 K and 176 K, respectively, in the temperature range between 10 K and 150 K. In this film, the total intensity of the Mössbauer spectra corresponding to the low-spin and high-spin sites drastically decreases above 200 K, reflecting the glass transition of Nafion, where the lattice vibration of [Fe(H-trz)₃]$_{\rm n}^{\,\,\rm 2n+}$ is softened just as in solution due to micro-Brown motion of the segment of Nafion polymer membrane.