Cobalt-centred boron molecular drums with the highest coordination number in the CoB16 cluster

Ivan A. Popov, Utah State University
Tian Jian, Brown University
Gary V. Lopez, Brown University
Alexander I. Boldyrev, Utah State University
Lai-Sheng Wang, Brown University


The electron deficiency and strong bonding capacity of boron have led to a vast variety of molecular structures in chemistry and materials science. Here we report the observation of highly symmetric cobalt-centered boron drum-like structures of CoB16, characterized by photoelectron spectroscopy and ab initio calculations. The photoelectron spectra display a relatively simple spectral pattern, suggesting a high symmetry structure. Two nearly degenerate isomers with D8d (I) and C4v (II) symmetries are found computationally to compete for the global minimum. These drum-like structures consist of two B8 rings sandwiching a cobalt atom, which has the highest coordination number known heretofore in chemistry. We show that doping of boron clusters with a transition metal atom induces an earlier two-dimensional to three-dimensional structural transition. The CoB16 cluster is tested as a building block in a triple-decker sandwich, suggesting a promising route for its realization in the solid state.