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 5p_π 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 [A_pM_pA_p]^x− (M = transition metals, A = main group elements, p = 3, 4, 5, …) sandwich ions and oligomers.