电场对金属串配合物M3(dpa)4Cl2 (M=Co,Rh, Ir; dpa=dipyridylamide)结构的影响

应用密度泛函理论PBE0 方法研究具有分子导线潜在应用的金属串配合物M₃(dpa)₄Cl₂ (1: M=Co, 2: M=Rh, 3: M=Ir; dpa=dipyridylamide)在电场作用下的几何和电子结构. 结果表明: 配合物基态均是二重态. 1和2的M₃⁶⁺金属链形成三中心三电子σ键, 3 中M₃⁶⁺形成三中心四电子σ键且存在弱的δ键. 随金属原子周期数增大其M―M键增强、LUMO与HOMO能隙减小、金属原子的反铁磁耦合减弱以至消失且自旋密度向配体的离域增强. 在Cl4→Cl5 电场作用下, 低电势端的M3－Cl5 键缩短, 高电势端的M2―Cl4 键增长, M―M平均键长略为缩短, M―M键增强, 有利于分子线的电子传递; 分子能量降低, 偶极矩线性增大. 低电势端Cl5的负电荷向高电势端Cl4 转移, 且3 中金属原子的正电荷由高电势端向低电势端的转移较明显, 自旋电子由低电势端向高电势端金属原子移动, 但桥联配体dpa^-与M和Cl 所在的分子轴间没有电荷转移. 电场使LUMO与HOMO能隙减小, 有利于分子的电子输运. 随金属原子周期数增大, 电场作用下M―M平均键长变化减小, LUMO、HOMO的能级交错现象减少.

Effects of Electric Field on the Structures of Metal String Complexes M3(dpa)4Cl2 (M=Co,Rh, Ir; dpa=dipyridylamide)

As potential molecular wire species, the geometrical and electronic structures of metal string complexes M₃(dpa)₄Cl₂ (1: M=Co, 2: M=Rh, 3: M=Ir; dpa=dipyridylamide) were investigated theoretically using density functional theory with the PBE0 functional by considering the interaction of an external electric field along the M₃⁶⁺ linear metal chain. The results show that the ground states of the complexes are all doublets. There is a 3-center-3-electron σ bond delocalized over the M₃⁶⁺ chain for 1 and 2, while there is a 3-center-4-electron σ bond and a weak δ bond among the Ir₃⁶⁺ chain in 3. Moving down the column of Co, Rh, and Ir elements in the periodic table, the complexes with the corresponding metals showed some regular trends, such as stronger M－M bonds, smaller LUMO-HOMO gaps, weaker anti-ferromagnetic spin coupling among the M₃⁶⁺ chains, and stronger spin delocalization from M₃⁶⁺ to ligands. In the external electric field along the Cl4→Cl5 direction, the M3 ― Cl5 bonds at the low potential side tend to be shortened, while the M2―Cl4 distances at the high potential side increase. With the increase of electric field, the average M―M distances slightly decrease, which is beneficial for electron transport. When the electric field increases, the molecular energy decreases and the dipole moment linearly increases. Moreover, the negative charge moves from Cl5 at the low potential end towards Cl4 at the high potential end, and the spin electron moves from M3 at the low potential end to M1 and M2 at the high potential end, while the positive charges transfer in the opposite direction along the M₃⁶⁺ chain of 3. However, there is no charge transfer between dpa^- ligands and M₃⁶⁺ chain or Cl^- ligands. The LUMO-HOMO gaps decrease with increasing electric field, which is beneficial for electron transfer. The sensitivity of the frontier orbitals to the electric field is different, which leads to the orbital level crossing for LUMO or HOMO. Moving down the column of metal elements in the periodic table, the complexes with the corresponding metals showed weaker orbital level crossing for LUMO or HOMO and smaller deviation of average M―M distances due to the effect of the electric field.