Investigation on the Coordination Bonding Nature of Actinide-Doped Endohedral Borospherenes An@B400/+/− (An = U, Np, Pu, Am, Cm)

Endohedral metallo-borospherenes M@B₄₀ have received considerable attention since the discovery of B₄₀ in 2014. However, the coordination bonding nature of most of actinide-doped endohedral An@B₄₀ still remains in dispute or unexplored. Extensive and systematic first-principles theory calculations performed herein unveil the ground states of triplet U@B₄₀ (<b>1</b>, <i>C</i>_2<i>v</i>, ³A₂), quartet U@B₄₀^- (<b>2</b>, <i>C</i>_2<i>v</i>, ⁴B₁), quintet Np@B₄₀⁺ (<b>3</b>, <i>C</i>_2<i>v</i>, ⁵A₁), sextet Np@B₄₀ (<b>4</b>, <i>C</i>₂, ⁶A), septet Pu@B₄₀ (<b>5</b>, <i>C</i>_2<i>v</i>, ⁷A₂), octet Am@B₄₀ (<b>6</b>, <i>C</i>_2<i>v</i>, ⁸A₂), and octet Cm@B₄₀⁺ (<b>7</b>, <i>C</i>_2<i>v</i>, ⁸A₂) at the coupled-cluster with triple excitations CCSD(T) level. Detailed principal interacting spin orbital (PISO) and adaptive natural density partitioning (AdNDP) analyses reveal their coordination bonding patterns and show that, with the numbers of unpaired <i>α</i>-electrons in parallel spins varying from n_α = 2, 3, 4, 5, 6, 7, to 7 in these complexes, the percentage contribution of the An 5f-involved PISO pairs to overall coordination bonding interactions decreases monotonously from 41% to 1%, and the contribution of An 6d-involved PISO pairs increases monotonously from 47% to 72%, while the marginal contribution of An 7s-involved PISO pairs remains basically unchanged (4~7%). The IR, Raman, and photoelectron spectra of the most concerned species are computationally simulated to facilitate their characterizations in future experiments.