Observation of highly stable and symmetric lanthanide octa-boron inverse sandwich complexes

Significance Lanthanide borides constitute an important class of materials with wide industrial applications, but clusters of lanthanide borides have been rarely investigated. It is of great interest to study these nanosystems, which may provide molecular-level understanding of the emergence of new properties and provide insight into designing new boride materials. We have produced lanthanide boride clusters and probed their electronic structure and chemical bonding. Two Ln 2 B 8 − clusters are presented, and they are found to possess inverse sandwich structures. The neutral Ln 2 B 8 complexes are found to possess D 8h symmetry with strong Ln–B 8 bonding. A unique (d–p)δ bond is found to be important for the Ln–B 8 –Ln interactions. The Ln 2 B 8 inverse sandwich complexes broaden the structural chemistry of the lanthanide elements and provide insights into bonding in lanthanide boride materials.