Stability and chemical bonding in a series of inverse sandwich actinide boride clusters (An 2 B 8 ) with δ bonding.

An inverse sandwich structure has been computationally predicted for uranium boride and extended to the series of actinide elements (An) from Th to Cm. The electronic structure and chemical bonding of these novel compounds have been analyzed using density functional theory and multireference wave-function based methods. We report the trends in electronic structure and bonding for An 2 B 8 , and found that (d-π)π and (d-p)δ are the most important factors in the stability of An 2 B 8 . The (f-p)δ bond provides extra stabilization for Pa 2 B 8 and U 2 B 8 , owing to the extensive interactions of An-B 8 -An, resulting in a short distance for the Pa-Pa and U-U bonds.