Aluminum Siting in Silicon-Rich Zeolite Frameworks: A Combined High-Resolution 27Al NMR Spectroscopy and Quantum Mechanics / Molecular Mechanics Study of ZSM-5
Stepan Sklenak, Jií Ddeek, Chengbin Li, Blanka Wichterlová, Vendula Gábová, Marek Sierka, Joachim Sauer
Angewandte (2007)46, 7286.
Finding Al: The distribution of catalytically active sites over crystallographic positions in zeolites is not random but controlled by synthesis. For differently synthesized ZSM-5 samples, distinct 27Al resonances have been identified by NMR spectroscopy. Shift calculations by DFT show that the observed resonances belong to Al in different crystallographic sites.
Structural and dynamical properties of guest molecules confined in mesoporous silica materials revealed by NMR
Gerd Buntkowsky, Hergen Breitzke, Anna Adamczyk, Frank Roelofs, Thomas Emmler, Egbert Gedat, Bob Grünberg, Yeping Xu, Hans-Heinrich Limbach, Ilja Shenderovich, Anastasia Vyalikh and Gerhard Findenegg
In the last fifteen years several novel porous silica materials, which are periodically structured on the mesoscopic length scale, have been synthesized. They are of broad interest for fundamental studies of surface–substrate interactions, for studies of the dynamics of guest molecules in confinement and for studies of the effect of confinement on the structural and thermophysical properties of fluids. Examples of such confinement effects include the change of the freezing and melting points or glass transitions of the confined liquids. These effects are studied by combinations of several NMR techniques, such as 15N- and 2H-solid-state NMR line shape analysis, MAS NMR and NMR diffusometry with physico-chemical characterization techniques such as nitrogen adsorption and small angle diffraction of neutrons or X-rays. This combination does not require crystalline samples or special clean and well defined surfaces such as conventional surface science techniques, but can work with typical ill-defined real world systems. The review discusses, after a short introduction, the salient features of these materials and the applied NMR experiments to give the reader a basic knowledge of the systems and the experiments. The rest of the review then focuses on the structural and dynamical properties of guest molecules confined in the mesoporous silica. It is shown that the confinement into the pores leads to fascinating new features of the guests, which are often not known for their bulk phases. These features depend strongly on the interplay of the their interactions with the silica surface and their mutual interactions.
Solid-state NMR opf endoheral hydrogen-fullerene complexes
M. Carravetta, A. Danquigny, S. Mamone, F. Cuda, O. G. Johannessen, I. Heinmaa, K. Panesar, R. Stern, M. C. Grossel, A. J. Horsewill, A. Samoson, M. Murata, Y. Murata, K. Komatsu and M. H. Levitt
We present an overview of solid-state NMR studies of endohedral H2-fullerene complexes, including 1H and 13C NMR spectra, 1H and 13C spin relaxation studies, and the results of 1H dipole–dipole recoupling experiments. The available data involves three different endohedral H2-fullerene complexes, studied over a wide range of temperatures and applied magnetic fields. The symmetry of the cage influences strongly the motionally-averaged nuclear spin interactions of the endohedral H2 species, as well as its spin relaxation behaviour. In addition, the non-bonding interactions between fullerene cages are influenced by the presence of endohedral hydrogen molecules. The review also presents several pieces of experimental data which are not yet understood, one example being the structured 1H NMR lineshapes of endohedral H2 molecules trapped in highly symmetric cages at cryogenic temperatures. This review demonstrates the richness of NMR phenomena displayed by H2-fullerene complexes, especially in the cryogenic regime.