C–Al TRAPDOR and REDOR Experiments for the Detection of C–Al Dipolar Interactions in Solids

We report ¹³C–²⁷Al double resonance experiments (REDOR and TRAPDOR) on several aluminum organic compounds with the aim of detecting ¹³C–²⁷Al dipolar couplings and distances in solids. The ¹³C and ²⁷Al pulses are applied to the same probe channel because their resonance frequencies are in close proximity. The different possibilities of controlling the efficiency of the TRAPDOR approach (by varying the ²⁷Al RF amplitude and the MAS frequency) are investigated. The results indicate that TRAPDOR is superior to REDOR in resolving differences in ¹³C–²⁷Al distances when choosing the proper experimental conditions. Where known, the crystal structure data are in qualitative agreement with the distance information extracted from our experiments. The experiment should be very valuable in different fields of solid state chemistry, where the interaction of organic and inorganic sample fractions is of fundamental importance.