Planar Octacoordinate Aluminium in Dual Aromatic AlBe4N4- Cluster

Abstract

High level quantum chemical methods based on density functional theory and coupled cluster have been carried out to predict AlBe4N4- cluster containing a planar octacoordinate aluminium centre. The neutral cluster has a quasi-planar structure in which the central Al atom lies only 0.30 angstrom above the molecular plane. The global minimum of the anionic cluster is perfectly planar and features dual aromaticity (orthogonally delocalized (4n + 2; n = 1) sigma and pi orbitals in the Huckel framework) and it is thermodynamically very stable. The dual aromatic behaviour of this cluster comes from the planarity of the ring, delocalized (4n + 2) sigma and pi bonds which has been supported by Shannon aromaticity index and sigma,pi-separated electron localization function analyses. The anionic cluster has been found to have profound Lewis acidity. The calculated gas phase fluoride ion affinity and its reaction with tetrahydrofuran reveal that the proposed cluster has profound Lewis acidic character. [GRAPHICS] .