Portal de Periódicos da CAPES

A High-Resolution 17 O and 29 Si NMR Study of Zeolite Siliceous Ferrierite and ab Initio Calculations of NMR Parameters

2000; American Chemical Society; Volume: 122; Issue: 20 Linguagem: Inglês

10.1021/ja993339y

1943-2984

Lucy M. Bull, Beate Bussemer, Tiit Anupõld, Andres Reinhold, Ago Samoson, Joachim Sauer, Anthony K. Cheetham, R. Dupree,

NMR spectroscopy and applications

High resolution 17O NMR spectra of siliceous ferrierite (Sil-FER) have been collected and the 29Si and 17O isotropic chemical shifts and the electric field gradients of oxygen have been calculated from first principles. The theoretical 29Si MAS NMR spectrum is found to be in excellent quantitative agreement with the experimentally determined spectrum, and is extremely sensitive to the accuracy of the structure used for the calculations, thus providing a method for assessing the quality of the structure determination. However, theoretical predictions of the chemical shifts, quadrupolar coupling constants and asymmetry parameters show only qualitative agreement with the experimental 17O NMR spectra obtained by Double Rotation (DOR) and multiple quantum magic angle spinning (MQMAS) as the spectra are much more complex (10 peaks within a shift range of less than 15 ppm, and the quadrupolar coupling constants only differ by 0.4 MHz) and hence higher accuracy is required from the shift calculations (>0.5 ppm), which is currently not possible. These findings also demonstrate the current limitations of the experimental techniques and show that no simple correlation appears to exist between the zeolite structure, such as the Si−O−Si bond angles or lengths, and the 17O NMR parameters.