Highly T_h-Symmetric Li₁₂H₁₃^- Cluster: An Archimedean Cage with Cavity-Bound Hydrogen

The structures, stabilities, and bonding characteristics of negatively charged lithium hydride clusters remain insufficiently explored. Here, we examine the potential energy surfaces of Li₁₂H₁₂^- and Li₁₂H₁₃^- using high-level electronic structure calculations. Li₁₂H₁₂^- adopts a highly symmetric T_h cage composed of fused four- and six-membered (Li-H)_n rings, closely resembling a truncated octahedron. In this anion, the excess electron localizes as a central non-nuclear attractor, forming a pseudoatomic species stabilized by the surrounding Li⁺ framework. Addition of one hydrogen atom produces Li₁₂H₁₃^-, whose global minimum also retains T_h symmetry but features a central hydrogen atom engaged in mixed electrostatic-covalent interactions with the Li₁₂H₁₂ cage, giving rise to a cavity-bound hydrogen center in an isolated cluster. These findings uncover previously unrecognized structural and bonding motifs in lithium hydride clusters and broaden the conceptual framework for electron localization and electrostatic interactions in metal hydride chemistry.