title: Theoretical studies on the bonding and electron structures of a [Au3Sb6](3-) complex and its oligomers.
abstract: Recently an all-metal aromatic sandwich compound of a [Sb3Au3Sb3](3-) ion has been synthesized and characterized experimentally, which indicates that there might exist a variety of stable all-metal sandwich complexes. The intralayer and interlayer chemical bonding interaction in this system plays significant roles in their stability, chemical properties and functionalities. Here we report a systematic theoretical study on the geometries, electronic structures, and chemical bonding of the [Sb3Au3Sb3](3-) ion and its congeners of [X3Au3X3](3-) (X = N, P, As, Sb, Bi, Uup) as well as [X3M3X3](3-) (M, X = Cu, As; Ag, Bi; Au, Sb; Rg, Uup) to understand the special stabilities of these species. Additional studies are also performed on the oligomers [Sb3(Au3Sb3)n](3-) (n = 1-4) to explore whether the sandwich compound can form stable extended systems. Through extensive theoretical analyses, we have shown that among the [Au3X6](3-) (X = N, P, As, Sb, Bi, Uup) species, [Sb3Au3Sb3](3-) is most stable due to superb matching of Sb3 and Au3 in both geometric size and fragment orbital energies. The significant stability of the [Au3Sb6](3-) ion is determined by the interlayer (p-d-p)σ interactions between the vertical Au 5d6s hybrid orbitals of Au3 and Sb 5pπ orbitals of the Sb3 rings. Each Sb3 ring demonstrates unique σ aromaticity, which remains when the complex is extended to oligomers. The results suggest that it is likely that there might exist other stable [ApMpAp](x-) (M = transition metals, A = main group elements, p = 3, 4, 5, …) sandwich ions and oligomers.
authors.affiliation: Department of Chemistry & Key Laboratory of Organic Optoelectronics and Molecular Engineering of the Ministry of Education, Tsinghua University, Beijing 100084, China. junli@tsinghua.edu.cn.
authors.forename: Wan-Lu
authors.initials: WL
authors.lastname: Li
authors.forename: Cong-Qiao
authors.initials: CQ
authors.lastname: Xu
authors.forename: Shu-Xian
authors.initials: SX
authors.lastname: Hu
authors.forename: Jun
authors.initials: J
authors.lastname: Li