Triple-quantum magic angle spinning Al-27 NMR of aluminum hydroxides

We show that 27Al triple-quantum magic angle spinning (3Q-MAS) experiments alleviate the second-order quadrupolar broadening to reveal the structure-building units of nonequivalent aluminum octahedra in the most extensively studied aluminum hydroxides, namely, gibbsite, bayerite, and boehmite. Further, aided by ab initio calculations of the electric field gradient tensors, the 3Q-MAS/MAS results are shown to lead to the assignment of 27Al isotropic resonances to the aluminum positions in their X-ray-determined structures. The present work paves the way for future studies on various structurally transformed materials derived from these basic aluminum hydroxides.