Transition-metal-centered nine-membered boron rings: MⓒB9 and MⓒB9(-) (M = Rh, Ir).

We report the observation of two transition-metal-centered nine-atom boron rings, RhⓒB(9)(-) and IrⓒB(9)(-). These two doped-boron clusters are produced in a laser-vaporization supersonic molecular beam and characterized by photoelectron spectroscopy and ab initio calculations. Large HOMO-LUMO gaps are observed in the anion photoelectron spectra, suggesting that neutral RhⓒB(9) and IrⓒB(9) are highly stable, closed shell species. Theoretical calculations show that RhⓒB(9) and IrⓒB(9) are of D(9h) symmetry. Chemical bonding analyses reveal that these complexes are doubly aromatic, each with six completely delocalized π and σ electrons, which describe the bonding between the central metal atom and the boron ring. This work establishes firmly the metal-doped B rings as a new class of novel aromatic molecular wheels.