title: Theoretical studies on all-metal binuclear sandwich-like complexes M2(η 4-E 4) 2 (M=Al, Ga, In; E=Sb, Bi).
abstract: A series of all-metal binuclear sandwich-like complexes with the formula M(2)(η(4)-E(4))(2) (M=Al, Ga, In; E=Sb, Bi) was studied by density functional theory (DFT). The most stable conformer for each of the M(2)(η(4)-E(4))(2) species is the staggered one with D (4d) symmetry. The centred metal-metal bond in each M(2)(η(4)-E(4))(2) species is a covalent single bond, with the main contributors to these covalent bonds being the a(1) and e orbitals. For all these species, the interactions between the centred metal atoms and the all-metal ligands are covalent; η(4)-Sb (4) (2-) has a stronger ability to stabilize metal-metal bonds than η(4)-Bi (4) (2-). Nucleus-independent chemical shifts (NICS) values and molecular orbital (MO) analysis reveal that the all-metal η(4)-Sb (4) (2-) and η(4)-Bi (4) (2-) ligands in M(2)(η(4)-E(4))(2) possess conflicting aromaticity (σ antiaromaticity and π aromaticity), which differs from the all-metal multiple aromatic unit Al (4) (2-). In addition, all of these M(2)(η(4)-E(4))(2) species are stable according to the dissociation energies of M(2)(η(4)-E(4))(2) → 2 M(η(4)-E(4)) and M(2)(η(4)-E(4))(2) → 2 M + 2E(4), and these stable species can be synthesized by two-step substitution reactions: CpZnZnCp + 2E (4) (2-)  → [E(4)ZnZnE(4)](2-) + 2Cp(-) and [E(4)ZnZnE(4)](2-) + 2 M (2) (+)  → E(4)MME(4) + 2Zn(+).
authors.affiliation: Institute of Chemical Physics, Beijing Institute of Technology, Beijing, 100081, People's Republic of China.
authors.forename: Congzhi
authors.initials: C
authors.lastname: Wang
authors.forename: Xiuhui
authors.initials: X
authors.lastname: Zhang
authors.forename: Jian
authors.initials: J
authors.lastname: Lu
authors.forename: Qianshu
authors.initials: Q
authors.lastname: Li
mesh_terms: D000965:Antimony / Q000737:chemistry; D001729:Bismuth / Q000737:chemistry; D003198:Computer Simulation; D056831:Coordination Complexes / Q000737:chemistry*; D005708:Gallium / Q000737:chemistry; D007204:Indium / Q000737:chemistry; D008958:Models, Molecular; D011789:Quantum Theory; D013816:Thermodynamics; D015032:Zinc / Q000737:chemistry
chemical_list: D056831:Coordination Complexes; D007204:Indium; D000965:Antimony; D005708:Gallium; D015032:Zinc; D001729:Bismuth