Boron Runs Rings Around Metals

A multi-institution research team has created wheel-like TaB₁₀^– and NbB₁₀^– clusters that set a record for the highest coordination number in any planar molecule (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201107880). Alexander I. Boldyrev of Utah State University and Lai-Sheng Wang of Brown University and coworkers have often teamed up to engineer seemingly impossible molecular combinations, including the previous record-holding hypercoordinated planar species RuB₉^–. For three-dimensional molecules, the highest coordination so far is 14. Boldyrev’s group focuses on computational chemistry to determine whether the imagined molecules are physically plausible, and Wang’s group generates the species by laser vaporization of a target disk containing the elements of interest and confirms their existence in the gas phase by using photoelectron spectroscopy. They found that the TaB₁₀^– and NbB₁₀^– wheels are perfect decagons (shown) and are aromatic by virtue of their delocalized σ and π bonds. Chemists are interested in making these materials for their superconducting or semiconducting properties. In a separate result, Boniface P. T. Fokwa and Martin Hermus of Germany’s RWTH Aachen University succeeded in using solid-state synthesis methods to make Ti₇Rh₄Ir₂B₈, which contains a planar B₆ ring as a building block. This is the first example of an isolable compound containing a planar all-boron ring (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201106798).