Dipolar dephasing between quadrupolar and spin- 1 2 nuclei. REDOR and TEDOR NMR experiments on VPI-5

In this work we examine the use of dipolar-dephasing magic-angle spinning NMR to study mixed pairs of quadrupolar and spin- 1 2 nuclei in solids. Dipolar connectivities are examined in both directions between the ²⁷Al (I=5/2) spins in the very large pore aluminophosphate VPI-5, which is considered representative of a range of inorganic framework materials. Rotational-echo double-resonance (REDOR) and transferred-echo double-resonance (TEDOR) experiments are demonstrated, as well as a two-dimensional extension of the TEDOR experiment. These experiments restore the heteronuclear dipolar coupling under MAS conditions via a train of radiofrequency pulses, thereby providing information about connectivities and distances between coupled nuclei in these inorganic solids.