Which kind of binuclear sandwich-like compound is more stable in M2(η4 − E4)2 (M = B, Al, Ga; E = XYZ = BCO, BNN, CBO), the metal centered or the non-metal centered sandwich-like complex?

To investigate the difference between the non-metal centered and metal centered binuclear sandwich-like compounds, a series of novel non-metal centered and metal centered binuclear sandwich-like complexes M2(η4 − E4)2 (M = B, Al, Ga; E = XYZ = BCO, BNN, CBO) have been studied by the density functional theory (DFT). The bonding characters of each species are discussed by the natural bond orbital (NBO), atoms in molecules (AIM) and molecular orbitals (MO) analysis. The aromaticity of the stable structures is analysized by the criterion of the nucleus-independent chemical shifts (NICS). The thermodynamic stabilities of M2(η4 − E4)2 are investigated by the dissociation reactions and isomerization reactions. It is found that the E 4 2 - rings as the ligands can form the stable binuclear sandwich-like complexes, and the synthesis of M2(η4 − E4)2 in future is desirable. Moreover, the non-metal centered sandwich-like compounds are more stable than the metal centered ones and the CBO-based compounds are energetically favored than their BCO-based isomers. The main difference of the bonding nature between the non-metal centered and metal centered binuclear sandwich-like complex is the interaction between the centered atoms and the ligands: one is predominantly covalent and the other is mainly ionic.