New theoretical insight into high coordination number complexes in actinides-centered borane

Abstract

<p>The coordination number of a given element behaving to understand its chemistry shows a great interest, which greatly promotes the extension and development of new materials, but remains challenging. Herein we report a new record high coordination number (CN) for actinide established in the cage-like An(BH)<sub>24</sub> (An = Th to Cm) via using relativistic quantum chemistry methods. Analysis of U(BH)<sub>n</sub> (n = 1 to 24) confirms these series of systems being as geometric minima, with the BH as a ligand located in the first shell around the uranium. Contrast, global searches reveal the low CN half-cage structure for UB<sub>24</sub>, which is extended to the series of AnB<sub>24</sub> and prevails over the competing structural isomers such as cage. The intrinsic geometric difference for AnB<sub>24 </sub>and An(BH)<sub>24</sub> mainly arise from the B sp<sup>3</sup> hybridization in borane inducing strong interactions between An 5f6d7s hybrid orbitals and B 2p<sub>z</sub> orbitals in An(BH)<sub>24</sub> comparing to that of AnB<sub>24</sub>. The fundamental trend presents a valuable insight for future experimental endeavor searching for isolable complexes with high-coordination actinide and provides a new structural motif of boron clusters and nanostructures.<br></p>