金属四重键化合物M_2X_4(PMe_3)_4(M=Cr,Mo,W;X=F,Cl,Br,I)结构和电子光谱的密度泛函理论研究

Density Functional Theory Study on the Structures and Electronic Spectra of Quadruply Bonded Metal Compounds M_2X_4(PMe_3)_4 (M=Cr, Mo, W; X=F, Cl, Br, I)

采用密度泛函理论方法,在TZ2P-STO基组水平下,对金属四重键化合物M2Cl4(PMe3)4(M=Cr,Mo,W)和Mo2X4(PMe3)4(X=F,Cl,Br,I)的几何结构进行优化,分析了电子结构,并运用TDDFT方法对其低占据激发态进行了计算.考虑相对论效应的ZORA方法能够较好地重现M2X4(PMe3)4的几何结构.M2X4(PMe3)4的电子结构分析表明其d电子的组态为σ2π4δ2,前线轨道能级顺序为πlig<πd/σd<δd<δd*.金属原子和卤素配体的改变虽然使轨道能量发生变化,但没有影响轨道的排布顺序.TDDFT方法对M2X4(PMe3)4δd→δd*和πd→δd*跃迁能量的计算较为准确,对πlig→δd*(LMCT)跃迁能量的计算误差较大.金属原子、卤素配体以及相对论效应对激发能的影响可以根据分子轨道能级的变化给予解释.

The geometric and electronic structures of quadruply bonded metal dinuclear compounds M2Cl4（PMe3）4 （M=Cr, Mo, W） and Mo2X4（PMe3）4 （X=F, Cl, Br, I） have been investigated by means of density functional theory method with TZ2P-STO basis sets. It was shown that the title compounds can be accurately predicted by DFT included ZORA relativistic correction. The present calculations show that the ground state configurations of all quadruply bonded dinuclear compounds are σ^2π^4δ^2, and the energetic ordering of metal-metal orbitals is πlig〈πd/σd〈δd〈δd^＊. Although the orbital energy levels changed with different metal atoms and haloid ligands, the energetic ordering of orbitals is not exchanged. The electronic excitation energies of M2X4（PMe3）4 have been studied employing the time-dependent density functional theory （TD-DFT）. The effects of metal atoms, haloid ligands, and relativistic effect on these compounds were examined. The calculated transition energies are in fairly good agreement with experimental values and the spectral shifts trends predicted by TD-DFT compare well with available experimental data.