Planar Pentacoordinate Bromine in Global Minimum Br6Li5.

Abstract

Delocalized multicenter bonds play a crucial role in clusters with a planar hypercoordinate center(s), making it difficult for highly electronegative elements, especially halogen atoms, to achieve the planar hypercoordinate arrangement. Herein, we introduce a star-like cluster Br6Li5-, whose global minimum contains a planar pentacoordinate bromine (ppBr). In this cluster, the central ppBr atom coordinates with five alkali metal Li atoms, which in turn bridge an equal number of electronegative Br atoms in the periphery, leading to the formation of the binary cluster Br6Li5-. Remarkably, bonding analyses indicate that the planar pentacoordinate configuration of Br6Li5- is dominated by the electrostatic interactions between the central ppBr atom and the Li5Br5 framework rather than covalent interactions. Despite the absence of delocalized bonds, Br6Li5- is still a highly stable cluster with a wider HOMO-LUMO gap of 7.73 eV and a higher VDE of 7.55 eV. Therefore, Br6Li5- should be a promising candidate for future gas-phase generation and spectroscopic characterization.