Application of 57Fe Mössbauer Spectroscopy to a Study of the Difference in Interactions between Guest and Host Molecules among (R), (S) and Racemic Isomers for (2-Methylbutyl)-, (2-Phenylpropyl)- and (2-Phenylbutyl)ferrocenes Enclathrated in Deoxycholic Acid

Abstract

Abstract 57Fe Mössbauer spectroscopy was applied to determine the difference, if any, in the interactions between host and guest molecules among the (R)-, (S)- and racemic isomers for (2-methylbutyl)-, (2-phenylpropyl)- and (2-phenylbutyl)ferrocene-deoxycholic acid (DCA) clathrates. The (S) isomer is included into DCA, while the (R) isomer is not in the case of (2-phenylpropyl)ferrocene. There is no significant difference in the temperature dependences of the 57Fe Mössbauer spectra between the (S) and racemic isomers-DCA for (2-phenylpropyl)ferrocene. For 2-methylbutyl and 2-phenylbutyl derivatives, all isomers form DCA clathrates. 57Fe Mössbauer spectroscopy revealed a difference in the molecular motion of guest molecules in the DCA lattice among them. For the 2-phenylbutyl derivative, the (S) isomer-DCA clathrate has one solvated molecule per guest molecule, a racemic isomer-DCA 0.7 solvated molecule, while the (R) isomer includes no solvated molecule. There was a difference in the powder X-ray diffraction patterns among them. An interesting phase transition was observed in (S)- and racemic (2-phenylbutyl)ferrocenes-DCA, which was accompanied by a desolvation, and then a change of crystal structure to that of (R) isomer-DCA heated up to the same temperature. Such a phase transition was not observed in (R) isomer-DCA. 57Fe Mössbauer spectroscopy revealed that (R) isomer-DCA changes in lattice vibration around 160 K, while (S) isomer-DCA does not.