Solid-State Polarization-Transfer Experiments Involving Quadrupolar Nuclei

Historically, cross-polarization experiments [1,2] have been used to transfer spin coherence from abundant spins to a dilute spin system. Protons (*H) have been used almost exclusively as the source of strong nuclear polarization for cross-polarization experiments, although there have been some examples where other abundant nuclei have been used. Coupled with magic-angle spinning (MAS) NMR [3], cross-polarization techniques have proven extremely powerful for the study of organic solids. Inorganic systems such as zeolites, gels, and ceramics are of great technological importance and interest and contain many quadrupolar nuclei but very few protons. For quadrupolar nuclei with non-integral spins such as n B , 1 7 O , and 2 7 A1 , the second-order quadrupolar broadening of the readily observed central (+1/2 <-> -1/2) transition is not completely averaged by MAS, and the NMR lines from quadrupolar spins are shifted and distorted in single-axis spinning experiments [4,5]. Very few examples exist of crosspolarization experiments involving quadrupolar nuclei, and they all involve magnetization transfer from protons to quadrupolar nuclei. We have undertaken a study to determine the feasibility of polarization transfer and dipolar dephasing experiments between spin pairs in these systems, particularly between 3 l P (I = 1/2) and A1 (I = 5/2). Our preliminary results show that these experiments are indeed possible [6],