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Molecular wheels: Decacoordinated molecular wheels, Ta©B10− (see picture) and Nb©B10−, showing the highest coordination number for the central atom in a planar environment at present, were produced in a laser-vaporization supersonic molecular beam and characterized by photoelectron spectroscopy and ab initio calculations. The highly symmetric Ta©B10− and Nb©B10− anions are doubly aromatic with six delocalized π electrons and ten delocalized σ electrons.
Galeev et al. (Wed,) studied this question.