UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Solid state NMR connectivity experiments involving quadrupolar nuclei Wong-Moon, Kirby Charles

Abstract

This thesis describes double-resonance solid-state NMR connectivity experiments involving quadrupolar and spin-1/2 nuclei. Cross-polarization, transferred-echo double-resonance (TEDOR), rotational-echo double-resonance (REDOR), and dipolar-dephasing difference experiments were used to determine connectivities via the heteronuclear dipolar-couplings between quadrupolar and spin-1/2 nuclei. Two-dimensional extensions of the cross-polarization and TEDOR experiments reveal connectivities between specific resonances in two-dimensional correlation spectra. Cross-polarization experiments were performed between 27Al and 31P nuclei in the aluminophosphate molecular sieves VPI-5 and AIPO4-8, and an experimental investigation of the parameters controlling the efficiency of the transfer is presented. REDOR, TEDOR, and dipolar-dephasing difference experiments are also demonstrated. Increased efficiency in cross-polarization experiments involving quadrupolar nuclei is obtained between 27Al and 31P spins in VPI-5 by carrying out the cross-polarization step with the spinning axis parallel to the applied magnetic field. After the cross-polarization step, the spinning axis is rapidly switched to the "magic angle" for detection of the high-resolution signal. The experiments developed for 27Al and 31P nuclei were extended to 27Al and 29Si nuclei for a series of representative zeolite frameworks, in which there is a relative enhancement of a given Si resonance which is approximately linear with the number of aluminum atoms in the neighbouring tetrahedral sites. Further extensions of the techniques to include 11B, 23Na, and 29Si nuclei are demonstrated for borosilicate glasses. The 27Al/ 31P and 27Al/29 Si connectivity experiments were used to determine the method of silicon substitution and reveal the presence of three types of aluminum environments in the sihcoaluminophosphate molecular sieve SAPO-37. The experiments. were also applied to the aluminophosphate AIPO4-5, confirming that the octahedral aluminum formed upon hydration remains bonded in the framework. For the first time, INEPT and DEPT experiments were performed in the solidstate. These experiments utilize coherence-transfer based on heteronuclear J-couplings to detect through-bond connectivities. Examples presented show that the experiments are applicable to both quadrupolar and spin-1/2 nuclei, and that only the +1/2 energy levels of the quadrupolar nuclei are involved in the coherence transfer.

Item Media

Item Citations and Data

Rights

For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.