Interface between alkylammonium ions and layered aluminophosphates materials: A combined theoretical and experimental study

n-Butylammonium ions intercalated in a layered aluminophosphate (AlPO-ntu) with kanemite-type structure (hereafter AlPO-kan) have been studied by IR spectroscopy and modeled with density functional theory (DFT) calculations. This joint approach clarified the local structure of the inorganic/organic interface, not yet described. The acidity of the surface hyroxyls was investigated with a finite cluster model, while the structure and the theoretical IR spectra were obtained with 3D and 2D periodic boundary conditions. In the structure here optimized, each organic ion forms three hydrogen bonds with the surface phosphate and aluminate oxygens; the theoretical frequencies, including anharmonic corrections on the main stretching modes, were compared to the experimental IR spectra. The very satisfactory agreement confirms the optimized structure and allowed all the observed peaks to be assigned, providing for the first time a clear-cut interpretation of the broad and complex absorption at 2800-1700 cm-1 in terms of Fermi-type resonances. © 2008 American Chemical Society.