SOLID-STATE DOUBLE-RESONANCE NMR EXPERIMENTS INVOLVING QUADRUPOLAR AND SPIN 1 2 NUCLEI/

In this work we describe coherence-transfer and dipolar-dephasing doub le-resonance NMR experiments that demonstrate spatial proximity of qua drupolar and spin 1/2 nuclei (other than protons) in solids. These exp eriments exploit heteronuclear dipolar couplings, whose magnitudes are proportional to the inverse third power of the internuclear distance and are therefore extremely sensitive to the separation of the coupled spins. Coherence transfer through cross-polarization is observed in b oth directions between Al-27 (I = 5/2) and P-31 (I = 1/2) nuclei in th e inorganic aluminophosphate framework systems VPI-5 and AlPO4-8, and an experimental investigation of the parameters controlling the effici ency of the transfer is presented. Dipolar-dephasing difference experi ments, rotational-echo double-resonance (REDOR), and transferred-echo double-resonance (TEDOR) experiments under magic-angle spinning condit ions are also demonstrated. Two-dimensional extensions of the cross-po larization and TEDOR experiments reveal the dipolar couplings between specific pairs of Al-27 and P-31 nuclei in two-dimensional correlation spectra, directly mapping connectivities from distinct sites with res olved NMR resonances.