Cu6Sc+ and Cu5Sc: Stable, high symmetry and aromatic scandium-doped coinage metal clusters

The Cu6Sc+ cation was detected experimentally as a stable bimetallic cluster [N. Veldeman, T. Hِltzl, S. Neukermans, T. Veszprémi, M.T. Nguyen, Phys. Rev. A. 76 (2007) 011201]. DFT calculations using the BP86 functional with various basis sets yield a D3h tricapped tetrahedron shaped structure as the most stable isomer. This cluster has a S2P6 electron configuration with a closed electronic shell, and its electrons tend to localize around Sc thereby fully occupying electron shell orbitals. Stability, high symmetry, and the NICS show that this cluster is aromatic. The neutral Cu5Sc cluster has the same electron configuration as Cu6Sc+. In agreement with qualitative predictions, DFT computations show that the C4v octahedron-shaped Cu5Sc cluster features a closed electronic structure and an aromatic character.