Pentagonal Star-like Three-Layered Aromatic Sandwich Structure of the [Li10Be2B5]+/0/- Cluster.

Abstract

Boron-based sandwich structures have garnered significant interest in recent years. However, species containing pentagonal boron rings are particularly rare. Herein, we theoretically predict an energetically low-lying three-layered sandwich structure of Li₁₀Be₂B₅^- (of D_5h symmetry). The central layer features a pentagonal planar B₅ ring staggeringly intercalated between two Be-centered pentagonal Li₅Be rings. Bonding analysis reveals that the entire cluster demonstrates σ/π aromaticity. Specifically, the inner B₅ layer contributes 6π/10σ-electron aromaticity, while each of the top and bottom layers contributes 2σ-electron aromaticity, leading to high symmetry in both the geometry and bonding patterns. Such a sandwich structure can also exist as the most stable conformation in both neutral and cationic states despite one of the delocalized σ bonds associated with the two outer Li₅Be layers being absent. Additionally, this aromaticity is clearly supported by a negative NICS_zz value and local diatropic contributions from the B₅ fragment. Our discovery enriches the sandwich family and provides a possible class of cluster units to form nanostructures.