密度泛函理论在分子磁学中的应用2.混合桥联三核镍配合物自旋交换作用

用密度泛函理论结合对称性破损方法(DFF-BS)研究了混合桥联三核镍配合物的磁交换耦合作用．这类化合物是由三唑和异硫氰酸根桥联形成的混合桥配合物．计算表明，在标题化合物中，三唑桥传递反铁磁耦合作用，而异硫氰酸根桥传递铁磁耦合作用；并且，随着异硫氰酸根取代三唑桥的数目增加，配合物的铁磁作用增强，在一定意义上说明了混合桥磁耦合作用的加合性．Mulliken自旋布居分析表明，无论是三唑桥还是异硫氰酸根桥，它们的磁交换作用机理都是磁中心的自旋离域．分子磁轨道分析显示，对于三唑桥，在局域磁轨道之间存在着强的轨道作用，导致了反铁磁耦合；对于异硫氰酸根桥，局域磁轨道之间弱的相互作用，表现了铁磁耦合作用．对标题化合物的研究说明了DFF-BS方法可用于三核体系磁交换作用的研究．

Application of Density Functional Theory to Molecular Magnetism 2.Magnetic Coupling Interaction in Mixed Bridged Trinuclear Nickel Complexes

Calculations on the magnetic coupling interaction in the mixed bridged trinuclear nickel complexes with triazole and isothiocyanate bridge ligands have been carried out by using the density functional theory combined with the broken symmetry approach (DFT-BS). It is found that in the title complexes the coupling interaction of the triazole bridge is antiferromagnetic while the isothiocyanate bridge transfers a ferromagnetic coupling. As increasing the number of isothiocyanate bridge the ferromagnetic characteristic is enhanced. The Mulliken population analyses show that in the title complexes there is a spin delocalization mechanism of magnetic coupling through the bridges. From molecular magnetic orbitals, it is shown that there is a stronger orbital interaction among the local magnetic orbitals through the triazole bridge, while isothiocyanate bridge gives rise to a weaker orbital interaction among the local magnetic orbitals. It is important to note that the DFT-BS suitable to the transition metal binuclear complexes can be also applied to magnetic exchange interaction for the transition metal trinuclear complexes.