High-Resolution Aluminum-27 Solid-State Magic-Angle Sample-Spinning Nuclear Magnetic Resonance Spectroscopic Study of AlCl₃-Tetrahydrofuran Complexes

We have obtained²⁷A1 solid-state nuclear magnetic resonance (NMR) spectra of several A1C1₃-THF complexes, using “magicangle” sample-spinning (MASS) NMR at high field. Our results suggest that the isotropic chemical shifts (δ_j) occur in relatively well defined regions for 4-, 5-, and 6-coordinate species (AIC1₄⁻, ~103 ppm; A1C1_3·THF, ~99 ppm; trans-AlCl₃·2THF, ~60 ppm; trans-[AlCl₂(THF)₄]⁺, ~ 14 ppm), as found previously with aluminum oxo compounds. We also find that theoretically calculated average nuclear quadrupole coupling constants (e²qQ/h) (/ran5-[AlCl₂(THF)₄]⁺, ~6.3 MHz; trans-AlCl₃·2THF, ~4.6 MHz; A1C1₃-THF, ~3.0 MHz; A1C1₄⁻, 0 MHz) are in good accord with experimentally determined nuclear quadrupole coupling constants, determined from computer simulations of the MASS NMR spectra (trans-[AlCl₂(THF)₄]⁺, 6.4 MHz; trans-AlCl₃·2THF, 4.9 MHz; A1C1₃·THF, 4.7 MHz; A1C1₄⁻, 0.3 MHz). Both ²⁷Al δ_jand e²qQ/h determinations appear to be useful as probes of structure in these systems, and thus offer a facile means of monitoring various solid-state reactions.