金属串配合物[MoMoCo(npo)4(NCS)2]的配位结构及其与电场的关系

Coordination Structures of Metal String Complexes[MoMoCo(npo)4(NCS)2] and Relationship with External Electric Field

应用密度泛函理论B3LYP方法研究了具有分子导线潜在应用的金属串配合物[MoMoCo(npo)4(NCS)2](npo=1,8-萘基-2-酮)的配位结构及其受电场作用的影响。配位方式记为(n,m),其中n、m分别表示4个赤道配体npo^-的O与Co和Mo配位的个数:n=0,1,2,3,4;m=4,3,2,1,0。结果表明:(1)零电场下,基态能量高低为(0,4)>(4,0)>(3,1)≈(1,3)>(2,2),5种配位方式均可稳定存在且互为竞争态。Z方向偶极矩μ(Z)值大小为(0,4)(+)>(1,3)(+)>(2,2)(-)>(3,1)(-)>(4,0)(-)(+、-表示μ(Z)值的正负,与Z方向相同即为正,相反即为负),4个npo^-趋向越一致能量越高极性越大。(2)Mo-Mo具有四重键,键长随μ(Z)值减小而减小,而Mo-Co键长则相反。随μ(Z)值减小前线轨道中πNCS(1)轨道能降低,π'NCS(2)轨道能升高。(3)Z方向电场作用下,除(0,4)外所有配位方式的Mo1-N8键显著增长,结构不稳定。(4)电场作用下前线轨道能级交错,μ(Z)为正值的(0,4)、(1,3)的能隙E_(LUMO-HOMO)在-Z方向电场中降低更显著,μ(Z)为负值的(2,2)、(3,1)和(4,0)的能隙在Z方向电场中降低更显著。分子极性越大,随电场强度增强能隙降低越显著,分子导电性可能越好。(0,4)、(3,1)和(4,0)可能具有整流效应,但(3,1)和(4,0)的稳定性较低。

Metal string complexes,with the structure of linear metal chain helically wrapped by four equatorial ligands,have attracted extensively attention due to their unique electronic,magnetic,and potential applications in molecular electronics.Some factors such as difference of metal atoms,axial ligands and equatorial ligands would affect the physical properties of conductance and magnetic properties of metal string complexes.The diversity of equatorial ligands provides more possibilities for such changes.The coordination structures of metal string complexes[MoMoCo(npo)4(NCS)2](npo=1,8-naphthyl-2-ketone)with potential applications as molecular wires have been investigated using the density functional theory B3LYP method by considering the effects of an external electric field(EF).The coordination mode is denoted as(n,m),where n and m represent the number of oxygen atoms coordinated with the Co3 and Mo1,respectively,and n=0,1,2,3,4;m=4,3,2,1,0.The energies and polarities of these molecules increase gradually as the coordination modes of four npo-ligands become more and more consistent,but all of them can exist stably and compete with each other.The Mo-Mo quadruple bond exists in all molecules,and the bond length decreases with the decrease of the Z-direction dipole momentμ(Z).In addition,as the value ofμ(Z)decreases,the orbital energy ofπNCS*(1)decreases but that ofπNCS*(2)increases.The geometric and electronic structures of the five coordination modes change regularly under the action of electric field.Under the electric field effect of Z direction,the Mo1-N8 bond lengths of all coordination modes except(0,4)increase obviously,leading to structural instability.Moreover,the phenomenons of energy level interlacing in the frontier orbitals,and the reduction of LUMO-HOMO energy gap are related to the value ofμ(Z).Whenμ(Z)is positive,the energy gaps of(0,4)and(1,3)decrease more significantly under the electric field effect of-Z direction.However,whenμ(Z)is negative,the energy gaps of(2,2),(3,1)and(4,0)decrease more obviously under the electric field effect of Z direction.Therefore,the complexes of(0,4),(3,1)and(4,0)may have the rectification effect,but(3,1)and(4,0)are less stable.