On the way to the highest coordination number in the planar metal-centred aromatic Ta©B10- cluster: evolution of the structures of TaB(n)- (n = 3-8).

The structures and chemical bonding of TaB(n)(-) (n = 3-8) clusters are investigated systematically to elucidate the formation of the planar metal-centred aromatic borometallic cluster, Ta©B10(-) (the © sign is used to designate the central position of the doped atom in monocyclic structures in M©B(n)-type planar clusters), which was found previously to have the highest coordination number for a metal atom in a planar geometry. Photoelectron spectroscopy is combined with ab initio calculations to determine the global minima of the TaB(n)(-) clusters. We find that from TaB3(-) to TaB5(-) the boron atoms nucleate around the central Ta atom to form fan-like structures.