The Cu₇Sc Cluster is a Stable σ‐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.

The high stability of boron-doped lithium clusters Li5B, Li6B+/− and Li7B: A case of the phenomenological shell model

“…Similar to the electron localization function (ELF) approach, the ELI-D scheme [29] and its orbital decomposition are proved to be an effective tool to probe the chemical bonding in organic compounds as well as in transition metal compounds [30]. The ELI is defined as the integral of the electron density over micro-cell containing the same fraction of same-spin electron pairs.…”

Growth Mechanism and Chemical Bonding in Scandium‐Doped Copper Clusters: Experimental and Theoretical Study in Concert

“…The optimal bond lengths and the s-aromatic ten electron system, composed by the 4s valence electrons of the copper and scandium and the one d electron of the scandium atom, are the main reasons of the stability. This was elaborated in reference [45]. It should, however, be noted that the growth algorithm only yielded this cluster when starting from the relative high energy Cu 6 Sc-VII and Cu 6 Sc-VIII species, which suggests that growth paths yielding this cluster are expected to have relative high activation barriers.…”

“…It has been pointed out in our previous articles that the coordination of the scandium atom plays an important role in the stability of scandium-doped copper clusters. [2,45] Due to its empty d atomic orbitals, scandium is an electron acceptor; hence, these atomic orbitals combine with the orbitals of the copper backbone, which stabilizes the cluster if the coordination of the scandium is high. Indeed, Cu 2 Sc-I, in which the coordination of the central scandium is two, is more stable than the linear Cu 2 Sc-II isomer, in which the corresponding coordination number is one.…”

Four Decades of the Chemistry of Planar Hypercoordinate Compounds

“…[137] Similar configurations have been predicted in M@Au 6 (M = Sc, Ti,V ,Cr, Mn, Fe,Co, and Ni)clusters by Luo and co-workers in 2009. [138] Furthermore,p lanar heptacoordinated copper was computationally predicted in the Cu 7 Sc (D 7h )cluster (56)byNguyen and co-workers [139] in 2008 ( Figure 56). …”