All-boron aromatic clusters as potential new inorganic ligands and building blocks in chemistry

Small boron clusters as individual species in the gas phase are reviewed. While the family of known boron compounds is rich and diverse, a large body of hitherto unknown chemistry of boron has been recently identified. Free boron clusters have been recently characterized using photoelectron spectroscopy and ab initio calculations, which have established the planar or quasi-planar shapes of small boron clusters for the first time. This has surprised the scientific community, as the chemistry of boron has been diversely featured by three-dimensional structures. The planarity of the species has been further elucidated on the basis of multiple aromaticity, multiple antiaromaticity, and conflicting aromaticity.Although mostly observed in the gas phase, pure boron clusters are promising molecules for coordination chemistry as potential new ligands and for materials science as new building blocks. The use of pure boron species as novel ligands has commenced, suggesting many new chemistries are ahead of us.