title: The Cu7Sc cluster is a stable sigma-aromatic seven-membered ring.
abstract: Density functional theory calculations demonstrate that the global minimum of the Cu(7)Sc potential energy surface is a seven-membered ring of copper atoms with scandium in its center, yielding a planar D(7) (h) structure. Nucleus-independent chemical shifts [NICS(1)(zz) and NICS(2)(zz)] show that this cluster has aromatic character, which is consistent with the number of 4s electrons of copper and scandium plus the 3d electrons of scandium satisfying Hückel's rule. According to a canonical MO decomposition of NICS(1)(zz) and NICS(2)(zz), the MOs consisting of the 4s atomic orbitals are mainly responsible for the aromatic behavior of the cluster. The electron localizability indicator (ELI-D) and its canonical MO decomposition (partial ELI-D) suggest that a localized basin is formed in Cu(7)Sc by the copper atoms whereas the two circular localized domains are situated below and above the ring. The planar Cu(7)Sc cluster can thus be considered as a sigma-aromatic species. These findings agree with the phenomenological shell model.
authors.affiliation: Department of Chemistry and Institute for Nanoscale Physics and Chemistry (INPAC), University of Leuven, Leuven, Belgium.
authors.forename: Tibor
authors.initials: T
authors.lastname: Höltzl
authors.forename: Ewald
authors.initials: E
authors.lastname: Janssens
authors.forename: Nele
authors.initials: N
authors.lastname: Veldeman
authors.forename: Tamás
authors.initials: T
authors.lastname: Veszprémi
authors.forename: Peter
authors.initials: P
authors.lastname: Lievens
authors.forename: Minh Tho
authors.initials: MT
authors.lastname: Nguyen