Boron Cluster Structures and Chemical Bonding

Boron exhibits a remarkable capacity to form a diverse array of cluster architectures, ranging from planar sheets and quasi‐planar rings to three‐dimensional cages and drums. This structural richness stems from boron’s electron deficiency, which drives extensive delocalisation of both σ and π electrons and the formation of multi‐centre bonds. In small clusters, planar and quasi‐planar motifs prevail, often displaying aromatic character akin to classical hydrocarbons but extended through σ and π frameworks. As cluster size grows or in the presence of metal dopants, three‐dimensional motifs emerge, including hollow cages known as borospherenes, inverse sandwich complexes in which boron rings are flanked by metal atoms, and drum-like structures with extraordinarily high coordination numbers. Metal doping further enriches the bonding landscape by stabilising novel geometries, tuning aromaticity, and enabling unique oxidation states. Together, these developments reveal fundamental principles of skeletal electron counting, aromatic delocalisation beyond Hückel’s rules, and the interplay between geometry and electronic structure, with implications for materials design, catalysis and nanoelectronics.

Research from Nature Portfolio

Recent studies have uncovered a new class of metallo‐borospherenes in which lanthanide atoms are integral to the cage surface rather than simply encapsulated, yielding hollow B₁₈ frameworks with triangular motifs and D₃h symmetry that challenge conventional fullerene chemistry. In parallel, investigations of small lanthanide-doped octa-boron clusters have revealed rare monovalent oxidation states coordinated by doubly aromatic η⁸-B₈ ligands, introducing “borozenes” as analogues to classical aromatic molecules. These findings have expanded the range of stable oxidation states and magnetic properties accessible in boron–metal clusters. Another breakthrough has been the isolation of lithium-doped B₁₃ clusters that adopt tetrahedral-ligand half-surround configurations, demonstrating robust stability through a combination of multi-centre B–B σ bonds and strong Li–B interactions, and suggesting routes to metallo-borophene nanomaterials.

Boron Cluster Structures and Chemical Bonding publication trend

The graph below shows the total number of articles in boron cluster structures and chemical bonding across all publications each year (not limited to Nature Index journals).

Technical terms

Aromaticity: Delocalisation of π or σ electrons over a cyclic or spherical framework, imparting enhanced stability.

Multi-centre two-electron bond: A bonding interaction in which two electrons are shared among three or more atoms rather than confined to a pair.

Endohedral cage: A hollow cluster structure that encapsulates one or more atoms within its interior.

Inverse sandwich complex: A motif in which a cyclic boron ring is coordinated on both faces by metal atoms.

Quasi-planar structure: A cluster geometry that is nearly flat with slight out-of-plane distortions to optimise bonding.

References

1. Boron-Based Inverse Sandwich V2B7− Cluster: Double π/σ Aromaticity, Metal–Metal Bonding, and Chemical Analogy to Planar Hypercoordinate Molecular Wheels. Molecules (2023).
2. Cobalt-centred boron molecular drums with the highest coordination number in the CoB16− cluster. Nature Communications (2015).
3. Competition between drum and quasi-planar structures in RhB 18 − : motifs for metallo-boronanotubes and metallo-borophenes. Chemical Science (2016).
4. [La(η x -B x )La] − ( x = 7–9): a new class of inverse sandwich complexes. Chemical Science (2019).
5. Spherical trihedral metallo-borospherenes. Nature Communications (2020).
6. Monovalent lanthanide(I) in borozene complexes. Nature Communications (2021).
7. Structure evolution of chromium-doped boron clusters: toward the formation of endohedral boron cages. RSC Advances (2019).
8. LiB13: A New Member of Tetrahedral-Typed B13 Ligand Half-Surround Cluster. Scientific Reports (2020).