Experimental and computational evidence of octa- and nona-coordinated planar iron-doped boron clusters: Fe©B8− and Fe©B9−

We report the observation of two Fe-doped boron clusters with wheel-type structures, containing an octa-coordinate (C8v-Fe©B8−) and a nona-coordinate (D9h-Fe©B9−) Fe atom. The clusters were produced in a laser vaporization supersonic molecular beam and characterized by combined photoelectron spectroscopy and ab initio studies. Chemical bonding analyses revealed that in the ground state both clusters are doubly (σ + π) aromatic and that the iron atom interacts with the peripheral boron ring exclusively through delocalized bonds. These findings provide further support to the design principle for metal-doped boron clusters with highly symmetric molecular wheel-type structures.