Designable Al32-oxo Clusters with Hydrotalcite-like Structures: Snapshots of Boundary Hydrolysis and Optical Limiting.

The hydrolysis of earth-abundant Al(III) has implications in mineral mimicry, geochemistry and environmental chemistry. The design and synthesis of third-order nonlinear optical (NLO) materials are important in modern chemistry due to their extensively optical applications. To study the hydrolysis and NLO properties, herein the assembly of Al(III) ions with π conjugated carboxylate ligands were carried out. As a result, a series of Al32-oxo clusters with hydrotalcite-like cores and π conjugated shells were isolated. Thanks to the accurate X-ray diffraction methods, the boundary hydrolysis snapshots that occur at equatorial unsaturated coordination sites of Al(III) ions are discovered. The charge distribution analysis and theoretical DFT calculations further supported proposed boundary substitution idea. Z-scan experiment results showed that the Al32-oxo clusters possess significant reverse saturable absorption (RSA) response with the minimal normalized transmittance up to 29%, indicating they are suitable candidates for optical limiting (OL) materials. This work is conducive to understanding the hydrolysis of Al(III) but also provides insight into the layered materials who also have strong boundary activity at the edges or corners.