The all non-metal homodinuclear and heterodinuclear sandwich-like compounds C ₂(η ³-L ₃) ₂ and BN(η ³-L ₃) ₂ (L = BCO, BNN and CBO)

Density functional theory studies on the all non-metal homodinuclear and heterodinuclear sandwich-like compounds C ₂(η ³-L ₃) ₂ and BN(η ³-L ₃) ₂ (L = BCO, BNN and CBO) have been performed. The staggered conformations of both C ₂(η ³-L ₃) ₂ and BN(η ³-L ₃) ₂ are predicted to be stable. The non-metal direct C-C and B-N bonds are covalent with σ interactions, which are formed by the interactions of s and p _z orbitals of the center atoms. Different from the ionic metal-ligand bond in the traditional metal center sandwich-like compounds, the C-L, B-L, and N-L bonds are covalent in these all non-metal sandwich-like compounds. The NICS values indicate that the ligands of C ₂(η ³-L ₃) ₂ and BN(η ³-L ₃) ₂, as well as their bare rings, display multiple aromaticity (σ and π aromaticity). Both σ and π aromaticity of the ring ligands towards the center atoms become stronger after complexation with the center atoms, while the π aromaticity against the center atoms is reduced. The π aromaticity of the ligands bonded to different center atoms follows a trend of B > C > N, and the (CBO) ₃ ⁺ ligands bonded to B possess the strongest π aromaticity. The dissociation reactions and possible synthetic reactions analysis show that these all non-metal sandwich-like compounds are stable, and the homodinuclear species are more stable than the heterodinuclear ones. These all non-metal binuclear sandwich-like compounds can be regarded as potential synthetic targets according to the highly negative free energies of the possible synthetic reactions. The isomerization reactions demonstrate that the CBO-based compounds should be more possible to synthesize in experiments than their BCO-based isomers.