title: The first binuclear sandwich-like complexes based on the aromatic tetraatomic species.
abstract: The first binuclear sandwich-like complexes based on the aromatic tetraatomic species with formula M(2)(η(4)-E(4))(2) (M = Al, Ga; E = N, P, As) have been studied by density functional theory (DFT). The stable conformer for each M(2)(η(4)-E(4))(2) is the staggered one with D(4d) symmetry except for Ga(2)(η(2)-N(4))(2) with C(2v) symmetry. Natural bonding orbital (NBO) analysis indicates that the metal-metal bonds of Al(2)(η(4)-E(4))(2) (E = N, P, As) and Ga(2)(η(4)-E(4))(2) (E = P, As) are all σ single bonds, which are derived mostly from the s and p(z) orbitals of the metal atoms by molecular orbital (MO) analysis. For M(2)(η(4)-E(4))(2) (M = Al, Ga; E = P, As), the metal-ligand interactions are covalent, while for Al(2)(η(4)-N(4))(2) the interactions between the Al atoms and the N(4)(2-) ligands are ionic. According to the calculated dissociation energies for breaking metal-metal bonds, the Al-Al and Ga-Ga bonds are very strong indicating that these stable sandwich-like compounds Al(2)(η(4)-E(4))(2) (E = N, P, As) and Ga(2)(η(4)-E(4))(2) (E = P, As) may be synthesized in future experiments. The nitrogen-rich compounds Al(2)(η(4)-N(4))(2) and Ga(2)(η(2)-N(4))(2) may be used as potential candidates of high energy density materials (HEDMs). Nucleus-independent chemical shifts (NICS) values reveal that the E(4)(2-) rings in the Al(2)(η(4)-E(4))(2) (E = N, P, As) and Ga(2)(η(4)-E(4))(2) (E = P, As) species possess conflicting aromaticity (σ antiaromaticity and π aromaticity) and with the same ligands, the E(4)(2-) ligands in Ga(2)(η(4)-E(4))(2) have more aromaticity than those in Al(2)(η(4)-E(4))(2).
authors.affiliation: Key Laboratory of Cluster Science, Ministry of Education of China, Department of Chemistry, Beijing Institute of Technology, Beijing, 100081, PR China.
authors.forename: Congzhi
authors.initials: C
authors.lastname: Wang
authors.forename: Nan
authors.initials: N
authors.lastname: Li
authors.forename: Xiuhui
authors.initials: X
authors.lastname: Zhang
authors.forename: Lin
authors.initials: L
authors.lastname: Ji
authors.forename: Qianshu
authors.initials: Q
authors.lastname: Li