第一过渡系金属硅烯配合物的理论研究

Theoretical Study of the Complexes of First-row Transition Metals with SiH_2

以HF/ 6 311+G 基组研究了硅烯SiH2 同第一过渡系金属的配合物MSiH2 的分子轨道特征及键解离能 .MSiH2 为共平面构型 .其中基态的3TiSiH2 和4 CoSiH2 带有明显的双键特征 .M—Si键具有共价性质 .M—Si的键解离能 ,从Sc到Cu呈现周期性变化 ,这种变化趋势同M的金属离子激发能之间存在近似的线性关系 .

The HF/6-311+G~ basis set was used to study the characteristics of molecular orbitals and bond dissociation energies of the complexes, MSiH_2, of the first-row transition metals with SiH_2. The atoms in MSiH_2 are all coplanar, and M—Si bonds of ground state ~3TiSiH_2 and ~4CoSiH_2 show obviously the double bond characteristic. In ~4VSiH_2 and ~5CrSiH_2 there is the week single occupiedπ bond. The ~8MnSiH_2 with a high-spin eightet ground state has both of single occupiedσ andπ bonds, and chief component of itsσ andπ orbital are the Mn 4s and the Si 3p_x orbitals, respectively. Other ground state MSiH_2 have only a double occupiedσ single bond. The most of M—Si bonds are quite covalent. The formation of M—Siσ bonds can be considered as the interaction between one electron in 4s or 4p_z, or 3d orbital of M and other electron in Sisp hybrid orbital. The double occupiedπ bonds are also considered as the pairing of oneπ electron of SiH_2(~3B_1) with one 3d electron of M. All of the HSiH bond angles in MSiH_2 are closed to that in SiH_2(~3B_1). It means that the Si in MSiH_2 still keeps asp hybrid orbital similar to Si in SiH_2(~3B_1 states). The Sc—Si, V—Si and Ni—Si bonds are longer because their formation involves mainly the 4s orbitals of M. On the contrary, the Cu—Si bond is shorter since itsσ bond would involve primarily the M 3d_Z^2 \{obitals\}. The ~3TiSiH_2 and ~4CoSiH_2 have much shorter bond lengths and larger bond dissociation energies because of their double bond character. From Sc to Cu, the bond dissociation energies of M—Si change in periodic trend. There is an approximate linear relationship between the bond dissociation energies and the metal ion promotion energy.