Study of ion exchange and intercalation of organic bases in layered substrates by vibrational spectroscopy. Inelastic neutron scattering, infrared and Raman spectroscopies of aniline-inserted α-and γ-zirconium hydrogen phosphates

Abstract

The intercalation of aniline into layered zirconium phosphate of both α and γ structural modifications has been studied using powder X-ray diffraction and vibrational spectroscopy. The intercalate stoichiometries differ (two molecules aniline per atom Zr in α; one molecule aniline per atom Zr in γ) because of inherent structural differences in the internal surfaces of the phosphate layers. X-Ray diffraction indicates the α and γ-type zirconium phosphate layers to be retained in the respective compounds, with expanded interlayer distances. Infrared and Raman spectroscopies show that the anilinium ion is formed in the interlayer zone, but that proton transfer in the α-structured intercalate is incomplete. Incoherent inelastic neutron scattering has allowed the identification of all vibrations of the phenyl ring and, in particular, of the torsional mode of occluded anilinium. The relative frequencies of this mode in intercalates derived from α- and γ-zirconium phosphate suggest that the N—H⋯O hydrogen bond is stronger in the former, for reasons probably related to the lower basicity of the ‘half-exchanged’γ-ZrPO₄·HPO₄·C₆H₅NH₃, compared with α-Zr(PO₄)₂·2C₆H₅NH₃.