金属串配合物[MM'M″(dpa)_4(Cl)_2](M=Co,Ni;M',M″=Co,Rh)电子输运的理论研究

Electron Transport of Metal String Complexes of[MM'M″(dpa)_4(Cl)_2](M=Co,Ni;M',M″=Co,Rh)

采用密度泛函理论DFT/BP86方法研究金属串配合物[MM'M″(dpa)_4(Cl)_2][MM'M″=CoCoCo(1),CoCoRh(2),CoRhRh(3),Ni CoRh(4)]的结构和电子输运性质.结果表明,配合物1,2和4的最稳定自旋态均存在1个(MM'M″)6+的离域σ33键(σ2σnb1σ*0);但配合物3具有1个(MM'M″)6+的离域σ34键(σ2σnb2σ*0)和2个π35键(π4πnb4π*2),故Rh—Rh键和Co—Rh键较强; Rh的引入使M—M键增强,Ni的引入则使M—M键减弱,键强次序为Rh—Rh>Co—Rh>Co—Co>Ni—Co.配合物1～4的传输通道均含有π和σ型轨道.正偏压下,配合物2和3的电流大于配合物1和4的.负偏压下,配合物4中出现负微分电阻效应.配合物3中形成传输通道的σnbα/β和π*α/β轨道能级分裂明显,(MM'M″)6+对β自旋的π*轨道的贡献(88%)比α自旋(74%)的大,使β自旋的电子更易传输,具有较好的自旋过滤效应(70%～80%).

The electronic structures and transmission properties of metal string complexes [MM'M″(dpa)4·(Cl)2][MM'M″=CoCoCo(1);CoCoRh(2);CoRhRh(3);NiCoRh(4)] were investigated by density functional theory BP86 method. The results show that there is a delocalized 3-center-3-lectron σ bond of (MM'M″)^6+ among complexes 1, 2 and 4, while there are one delocalized 3-center-4-electron σ bond of (MM'M″)^6+ and two 3-center-5-electron π bonds in complex 3. The Rh-Rh bond of complex 3 is the strongest among complexes 1-4 and the Co-Rh bond is second on account of above-mentioned information. The substitution of Rh enhanced the M-M bond, and the replace of Ni weakened the M-M bond. In conclusion, the order of bond is Rh-Rh>Co-Rh>Co-Co>Ni-Co. The transport channels of complexes 1-4 contain π-type and σ-type orbitals. Under positive bias, the currents in complexes 2 and 3 are greater than complexes 1 and 4. Under negative bias, there is a negative differential resistance effect in complex 4. The energy splitting of σnbα/β and π^*α/β orbit as transport channels in complex 3 are the most obvious among complexes 1-4. Moreover, the contribution of (MM'M″)^6+ to the π^* orbit of β spin(up to 88%) is larger than that of α(up to 74%). Thus, the electronic transmission of β spin channel is stronger than α spin. To sum up, the complex 3 has significant spin filter effect (up to 70%-80%).