Multi-center bonding and structural integrity in M6M8B60 (M = Y, La, 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-borospherenes chemistry. Inspired by these findings, highly symmetric cage-like structures, M₆M₈B₆₀ (M=Y, La, Lu), has 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 (mc-2e) 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, HF). Encapsulation of Eu atom notably modulates the cage's properties, yielding the endohedral complex Eu@Y₆Y₈B₆₀ (Isomer I) with a magnetic moment of 7 μ_B localized on the Eu center. The weakly bound Eu-cage interaction highlights 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 boronbased nanocages with tailored electronic and magnetic properties.