Interface Between Alkylammonium Ions and Layered Aluminophosphates Materials: A Combined Theoretical and Experimental Study

Butylammonium ions intercalated in a layered aluminophosphate (AlPO-ntu) with kanemite-type structure (hereafter AlPO-kan) were studied by IR spectroscopy and modeled with d. functional theory (DFT) calcns. This joint approach clarified the local structure of the inorg./org. interface, not yet described. The acidity of the surface hyroxyls was studied with a finite cluster model, while the structure and the theor. IR spectra were obtained with 3-dimensional and 2-dimensional periodic boundary conditions. In the structure here optimized, each org. ion forms 3 hydrogen bonds with the surface phosphate and aluminate oxygens; the theor. frequencies, including anharmonic corrections on the main stretching modes, were compared to the exptl. IR spectra. The very satisfactory agreement confirms the optimized structure and allowed all the obsd. peaks to be assigned, providing for the 1st time a clear-cut interpretation of the broad and complex absorption at 2800-1700 cm-1 in terms of Fermi-type resonances