RE - B₇ (RE = Sc, Y, La - Lu): smallest rare - earth borozene complexes

Rare - earth (RE) elements, with their unique electronic configurations and exceptional properties, are indispensable in modern technology and materials science. This study conducts a comprehensive theoretical investigation using first - principles calculations. The results show that the smallest rare - earth borozene RE - B₇ (RE = Sc, Y, La - Lu) clusters adopt a half - sandwich RE³⁺[η⁷-B₇^3-] global - minimum structure, stabilized by the B₇^3- ligand's aromaticity and ionic - covalent hybrid bonding between RE³⁺ and B₇^3-. AdNDP chemical bonding analyses reveal six 2c - 2e σ(B - B) bonds, three 7c - 2e σ bonds, and three 8c - 2e π bonds, confirming the cluster's double aromaticity. Energy decomposition analyses indicate that the interaction between RE³⁺ and B₇^3- is predominantly electrostatic (62% - 69%) with significant orbital interaction contributions (31% - 38%). Molecular dynamics simulations demonstrate excellent dynamic stability at room temperature. The lanthanide contraction leads to shorter RE - B bonds and enhanced covalency across the lanthanide series. This work expands the scope of rare - earth chemistry, provides a theoretical framework for functional material design, and advances understanding of inorganic aromaticity and metal - cluster bonding.

The global - minimum (GM) structure search and vibrational frequency of RE-B₇ clusters were performed by using TGMin (v.3) package, respectively. To obtain more accurate results, the structures were re - optimized at the PBE/def2 - TZVP/RECP level with dispersion corrections by using ORCA package. Subsequently, the Mayer's total valence, Mayer's bonded valence, quantum - theory of atoms - in - molecules, interaction region indicator, reduced density gradient or non - covalent interactions analyses, binding energy, principal interacting orbital analyses, adaptive natural density partitioning chemical bonding analyses, energy decomposition analysis and natural orbital for chemical valence model analyses were also performed at the same level. The semi - empirical molecular dynamics simulations were performed by using the CP2K package. The 5000 fs SEMD simulations were then performed in the NVT canonical ensemble with Nose - Hoover Chain thermostat. The evolution of temperature, potential energy, radial distribution function and coordination number were also visualized to investigate the dynamics stability of the RE - B clusters.