57Fe Mössbauer Spectroscopic Studies of the Ferrocene Molecular Reorientation in AlPO4-5 and AlPO4-8 Frameworks.

Fe-57 Mossbauer spectroscopic studies were carried out on ferrocene guest molecules in some microporous aluminium phosphate host lattices in order to investigate their behaviour in the aluminium phosphate channels. The 300 K spectra show broad single lines with isomer shifts of 0.39 and 0.41 mm s-1 relative to iron for AlPO4-5:ferrocene and AlPO4-8:ferrocene inclusion compounds, respectively. The absence of quadrupole splittings for these materials contrasts with the large quadrupole splitting observed for ferrocene itself at the same temperature. The low-temperature spectrum (20 K) for AlPO4-5:ferrocene shows a doublet with quadrupole splitting of 2.37 mm s-1 and an isomer shift of 0.55 mm s-1. The collapse of the quadrupole splitting at room temperature is consistent with the ferrocene molecules rotating within the channels.