【摘要】 应用密度泛函理论B3LYP方法对金属串配合物[Co MCo(dpa)4(NCS)2](1:M=Co,2:M=Ni,3:M=Pd,4:M=Pt;dpa=二吡啶胺)的成键性质和自旋过滤效应进行了研究,结果表明:配合物1的基态为二重态,Co6+3金属链形成三中心三电子σ键(σ2σ1nbσ*0);而配合物2~4的基态均为反铁磁耦合单重态(AF态),对应的最低能量高自旋态(HS态)分别为三重态、七重态和七重态,单电子分布在两端Co原子上,[Co MCo]6+链具有三中心四电子σ键(σ2σ1nbσ*1).配合物1~4均具有自旋过滤效应,电子传输通道主要为β-自旋σnb轨道,与费米能级的距离大小为1<2<3≈4.电场作用下,1~4的高电势端Co2—N4键增长而低电势端Co3—N7键缩短,Co—M平均键长略为缩短,Co—M键增强;电场作用下金属原子的自旋密度和电荷密度变化很小,电磁性质稳定;电场作用下σnb轨道分布仍保持沿金属轴方向离域,LUMO-HOMO能隙减小,有利于电子输运.更多还原

【Abstract】 The bonding and spin filtering properties of metal string complexes [Co MCo( dpa)4( NCS)2]( M = Co,Ni,Pd,Pt; dpa = dipyridylamine) have been investigated with the density functional theory B3 LYP method. The results show that the ground state of complex 1 is doublet,and there is a 3-center-3-electron σ bond( σ2σ1nbσ* 0)delocalized over the Co6 +3chain. However,the ground states of complexes 2 ~ 4 are antiferromagnetic( AF) singlet,corresponded to the high spin configurations with two unpaired,six unpaired and six unpaired electrons,respectively. The unpaired electrons of complexes 2 ~ 4 largely localize on the terminal CoIIions and there is a 3-center-4-electron σ bond( σ2σ1nbσ* 1) delocalized over the [Co MCo]6 +chain. The molecular orbital energy level diagrams and PDOS diagrams show that the spin-β components of singly σnborbital are the dominant transport channel. Complexes 1 ~ 4 all possess spin filtering effect. The distance between spin-β components of σnborbital and Fermi levels is 1 < 2 < 3≈4. Under the electric field,the Co2—N4 bond lengths at the high potential side increase,while the Co3—N7 distances at the low potential side tend are shortened. The average Co—M distances,the spin densities and NPA charge of metal atoms are less affected by electric field,indicating the electromagnetic properties are stable. Under the electric field,the σnborbital still keeps delocalized along the metal chain and the LUMO-HOMO gaps decrease. This is beneficial for electron transfer.更多还原