金属串配合物(n,m)[Cr_3(PhPyF)_4Cl_2](n=2,3,4;m=2,1,0)的配位结构及其与电场的关系

Coordination Structures of Metal String Complexes(n, m)[Cr_3(PhPyF)_4Cl_2](n=2, 3, 4; m=2, 1, 0) and Relationship with External Electric Field

应用密度泛函理论BP86方法研究具有分子导线潜在应用的金属串配合物(n,m)[Cr3(Ph Py F)4Cl2](HPh Py F=N,N′-苯基吡啶基甲脒;n=2,3,4;m=2,1,0)的配位结构及其受电场作用的影响,n、m分别表示Ph Py F-的苯环在左侧和在右侧的配体个数.结果表明:(1)零电场下,四个Ph Py F-的(2,2)、(3,1)和(4,0)三种配位方式能量差别很小,为竞争态,(2,2)最稳定.(4,0)结构中两端轴向配体Cl均可与Cr配位,且Cl4―Cr1键比Cl5―Cr3键更强,若作为分子器件可与电极结合,这与(4,0)[Cu Cu M(npa)4Cl][PF6](M=Pd,Pt;Hnpa=2-萘啶苯胺)靠近苯环一端的轴向配体无法与M配位不同.(2)在(2,2)、(3,1)和(4,0)中,Cr36+链均具有三中心三电子离域σ键,但离域性逐渐减弱.随四个Ph Py F-配位方式趋于一致,分子极性逐渐增大,由Cl4指向Cl5(Z)方向,Cr1的α自旋密度增大,Cr2的β和Cr3的α自旋密度减小.(3)分子的几何结构和电子结构在电场下发生规律性变化,在-Z方向电场作用下,(3,1)、(4,0)电子移动方向与极性方向相同,使分子的键长、自旋密度、电荷和能隙变化显著性均大于Z方向电场,且极性越大变化越显著,有利于提高分子导电性.

The coordination structures of metal string complexes （n, m） [Cr3（PhPyF）4Cl2] （HPhPyF=N,N′-phenylpyridylformamidine; n=2, 3, 4; m=2, 1, 0） with potential applications as molecular wires have been investigated using the density functional theory BP86 method by considering the effects of an external electric＆amp;nbsp;field （EF）. Herein, n and m represent the number of benzene rings on the left and right in the PhPyF-ligand, respectively. The results show that：（1） under zero field, the three kinds of coordination modes （（2, 2）, （3, 1）, （4, 0）） of the four PhPyF-ligands are close in energy, which indicates that they are competitive conformations. The （2, 2） coordination mode is the most stable one. The Cl axial ligands on the two sides of （4, 0） can coordinate to Cr atoms, indicating that these two axial ligands can combine with electrodes. Moreover, the Cl4―Cr1 bond is stronger than Cl5―Cr3, different from （4, 0） [CuCuM（npa）4Cl] [PF6] （M=Pd, Pt; 2-naphthyridylphenylamine） in which the axial ligand Cl close to benzene cannot coordinate to metal atom M. （2） There is a 3-center-3-electron delocalizationσbond in the Cr36＋chain for （2, 2）, （3, 1）, and （4, 0）, but the delocalization gradual y weakens. The polarity from Cl4 to Cl5 is stronger as the coordination mode of four PhPyF- ligands becomes more consistent. （3） The geometry and electronic structure of the investigated complexes change regularly under the electric field. Because the electron transfer direction of （3, 1） and （4, 0） is the same as its molecular polarity, the bond length, spin density, charge and energy gap are more sensitive to-Z electric field. Therefore, the-Z elelctric field is beneficial to the conductivity of the molecules. Moreover, the sensitivity of the structures to electric field increases with polarity.