Study of ion exchange and intercalation of organic bases in layered substrates by vibrational spectroscopy. Part 1.—Inelastic neutron scattering, infrared and Raman spectroscopies of ammonium- and tetramethylammonium-exchanged α-tin hydrogen phosphate

Abstract

The nature of guest–host interactions has been studied in ammonium- and tetramethylammonium(TMA)-intercalated α-Sn(HPO₄)₂·H₂O(SnP), using a combination of infrared, Raman and incoherent inelastic neutron scattering spectroscopies, in order to obtain information on such characteristics as the extent of proton transfer from the acidic sites on internal surfaces to interlayer molecules, the relative freedom of movement of the intercalate, and the site symmetry of the guest species. Ammonium ions are strongly hydrogen bonded to the macroanionic layers and infrared activity suggests the site symmetry of NH₄ to be reduced from ideal tetrahedral. Combined techniques indicate the skeletal vibrations of exchanged TMA to have spectroscopic activities and positions similar to the corresponding halides. However, the positions of the CH₃ torsional modes in inelastic neutron scattering demonstrate their sensitivity to the macrostructural environment and are consistent with weak SnP–TMA interactions.