Boron rings containing planar octa-and enneacoordinate cobalt, iron and nickel metal elements

For a series of boron rings with planar hyper-coordinate 8th group transition metal atoms, singlet (FeB8-2)-Fe-1, multiplet (FeB9n)-Fe-k (n = -1, k = 1; n = 0, k = 2), singlet (CoB8n)-Co-1(n = -1, +1, +3), multiplet (CoB9n)-Co-k (n = +1, k = 2; n = 0, k = 1) and singlet (NiB9+)-Ni-1, the geometry structures have been optimized to be local minima on corresponding potential hyper-surfaces. The electron structures are discussed by orbital analysis and the aromaticity is predicted by nucleus-independent chemical shifts calculation at both the B3LYP/6-311+G* and BP86/6-311+G* levels of theory, respectively. The results suggest that all these structures with high symmetry planar geometries are stable and have aromatic properties with six pi valence electrons.