Multi-center bonding and structural integrity in M6M8B60 (M = Y, La, and Lu) metallo-borospherenes

Abstract

Recent experimental discoveries of metallo-borospherenes, La₃B₁₈⁻/Tb₃B₁₈⁻, revealed boron's capacity to form fullerene-like cage architectures, representing a significant advance in metallo-borospherene chemistry. Inspired by these findings, highly symmetric cage-like structures, M₆M₈B₆₀ (M = Y, La, and Lu), have been proposed via first-principles calculations, where metal atoms are embedded on the cage surface. The M₆M₈B₆₀ cage, unlike the La₃B₁₈⁻/Tb₃B₁₈⁻ clusters, are constructed via a mixed-unit, topology-driven strategy involving six M©B₈ and eight M©B₉ motifs. This design does not represent a simple size expansion from smaller boron cages, but instead establishes a new cage topology featuring a larger cavity, higher symmetry, and a highly delocalized multi-center bonding network. Binary system investigations further reveal negligible electronic overlap between neighboring M₆M₈B₆₀ units, confirming that each cluster can maintain its molecular integrity and exist as a stable, independent entity. Electronic structure analysis uncovers 111 uniformly distributed multi-center two-electron bonds, which underpin the exceptional stability and delocalized bonding characteristics of these metallo-borospherenes. Moreover, the robust cage of Y₆Y₈B₆₀ provides a versatile host for encapsulating various atoms and small molecules (Eu, CH₄, CO, H₂, and HF). Encapsulation of the Eu atom notably modulates the cage's properties, yielding the endohedral complex Eu@Y₆Y₈B₆₀ (Isomer I) with a magnetic moment of 7μ_B localized on the Eu center. The electrostatic interaction and weakly bound Eu–cage interaction highlight the tunable host–guest behavior of this system. These results expand the structural and electronic diversity of metallo-borospherenes and provide valuable insights into designing large, multifunctional boron-based nanocages with tailored electronic and magnetic properties.