Probing the Nature of the Transition-Metal-Boron Bonds and Novel Aromaticity in Small Metal-Doped Boron Clusters Using Photoelectron Spectroscopy.

Abstract

Photoelectron spectroscopy combined with quantum chemistry has been a powerful approach to elucidate the structures and bonding of size-selected boron clusters (Bn-), revealing a prevalent planar world that laid the foundation for borophenes. Investigations of metal-doped boron clusters not only lead to novel structures but also provide important information about the metal-boron bonds that are critical to understanding the properties of boride materials. The current review focuses on recent advances in transition-metal-doped boron clusters, including the discoveries of metal-boron multiple bonds and metal-doped novel aromatic boron clusters. The study of the RhB- and RhB2O- clusters led to the discovery of the first quadruple bond between boron and a transition-metal atom, whereas a metal-boron triplebond was found in ReB2O- and IrB2O-. The ReB4- cluster was shown to be the first metallaborocycle with Möbius aromaticity, and the planar ReB6- cluster was found to exhibit aromaticity analogous to metallabenzenes.