电场作用下金属串配合物[Ru_3(dpa)_4]L_2(L=Cl,C≡N,C≡CPh)结构的理论研究

Theoretical Study on the Structures of Metal String Complexes[Ru_3( dpa)_4]L_2( L = Cl,C≡N,C≡CPh) under the Electric Field

用密度泛函理论BP86结合自然键轨道分析方法,研究了具有分子导线潜在应用的含二吡啶胺配体（dpa）的金属串配合物[Ru3（dpa）4]L2（1：L=Cl,2：C≡N,3：C≡CPh）的Ru—Ru,Ru—L键及其在电场作用下的结构变化规律,结果表明：（1）配合物基态均存在Ru6＋3离域三重键,1中具有1个σ43和2个!43离域键,2中具有σ23,!53和δ53离域键,3中具有1个σ23和2个!53离域键.1的轴向配体形成Ru—Cl弱配位σ键,2和3中Ru与C≡N和C≡CPh（下文简写为CN和CCPh）除形成Ru—C配位σ键外,还具有Ru（dyz,dxz）→L（!＊C-N或!＊C-C）反馈!键,减弱了Ru—Ru离域!键.且2的CN中N的电负性较大,其反馈!键更强使Ru—Ru键最弱,故Ru—Ru距离为2〉3〉1.（2）电场作用下,低电势端的Ru—Ru和Ru—L键缩短,而高电势端的Ru—Ru和Ru—L键增长;轴向配体的负电荷向高电势端转移,而Ru的正电荷则向低电势端移动;高电势端Ru的自旋密度减小,而低电势端Ru和L的自旋密度增大.因3中CCPh共轭性强,故电荷密度和自旋密度对电场更敏感,有利于电子在分子轴的传输.1-3的前线分子轨道分布、能级和能隙在电场作用下均较稳定.在电场中前线轨道仍能保持金属轴的离域,有利于电子传输.（3）含更大的共轭轴向配体CCPh的3的HOMO-LUMO能隙小于具有相同自旋态的2,故3的导电性可能最好.

As a potential molecular wire,metal string complexes [Ru3（ dpa）4]L2（ 1： L = Cl,2： C≡N,3： C≡CPh） under an external electric field along the Ru6 ＋3chain were investigated with the density functional theory at BP86 level and the Natural Bond Orbital Theory. It is found that：（ 1） For the ground states of 1 ~ 3,there are delocalized triply bonds through the Ru6 ＋3chain,such as one σ43and two !43bonds in 1,the σ23,!53and δ53bonds in 2,one σ23and two !53bonds in 3. The Ru—Cl interaction of 1 is only a weak σ coordinate bonding. Besides Ru—L σbonding in 2 and 3,there are Ru（ dyz,dxz） →L（ !＊C- Nor !＊C- C） !back-bondings,which weaken the Ru—Ru bonds. Notably,the stronger electronegativity of N in CN results in the stronger Ru→L !back-bonding and further weakens the Ru—Ru bond in 2. Therefore,the Ru—Ru distances are in the order of 2 3 1.（ 2） Under the effect of electric field,the Ru—Ru and Ru—L bond lengths at the low potential end tend to be decreased,while increasing at high potential end. Meanwhile,the negative charges of L move from low potential end toward high potential end,but the positive charges of Ru move to the opposite direction. The spin densities of the Ru at high potential end decrease,while those of Ru and L at low potential end increase. Due to the strong delocalization of CCPh axial ligand,the NPA charge and the spin density in 3 are more sensitive to external electric field,which isbeneficial to electron transportation along the Ru6 ＋3chain. The frontier molecular orbital distributions,energy levels and HOMO-LUMO gaps of 1 ~ 3 are not sensitive to external electric field. The frontier molecular orbitals are still delocalized along the metal axial with the increasing of external electric field. These properties about frontier molecular orbitals are beneficial to electron transportation.（ 3） The HOMO-LUMO gap of 3 with the strongest conjugated CCPh ligand is smaller than 2 which has the same ground state as 3. Therefore,it is probable that the conductivity of 3 is the best among complexes 1 ~ 3.