H2 Elimination from Hydrated Aluminum Clusters: Acid−Base Reaction Mediated by Intracluster Proton Transfer

The reactivity of different [Al,20H 2 O] + clusters was investigated using gradient-corrected DFT. In clusters with the stoichiometry [AlH(OH)(H 2 O) 19 ] +, which contain a four-fold-coordinated Al III, H 2 formation was found to occur according to the following mechanism: First a proton is released within the cluster by hydrolysis of a first shell H 2 O. By successive proton-transfer reactions in the hydrogen-bonded network of the cluster, the proton migrates to the hydridic H at the Al III cation. Finally, hydride ion and proton recombine to H 2 in an acid−base reaction. The activation barrier for this process was determined to be 45 kJ mol -1 . No H 2 formation was found in hydrated Al I clusters, [Al I (H 2 O) 20 ] + .