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.