异双核X-M之间的磁耦合交换作用:Keggin型杂多酸衍生物[M(H_2O)XW_(11)O_(39)]^(7-)(X=Fe~Ⅲ,Co~Ⅲ;M=Co~Ⅱ)的密度泛函研究

Density Functional Studies of Magnetic Exchange of Biheteroatom 11-Heteropoly Complexes:[M(H_2O)XW_(11)O_(39)]^(7-)(X=Fe~Ⅲ,Co~Ⅲ;M=Co~Ⅱ)

采用DFT-BS方法研究异双核的Keggin型杂多酸衍生物[M(H2O)XW11O39]7-(Ⅰ:X=FeⅢ,M=CoⅡ;Ⅱ:X=CoⅢ,M=CoⅡ)的磁耦合作用,计算得到耦合常数(J)为负值,表明所研究体系具有反铁磁性;J值大小顺序为|J(Ⅰ)|<|J(Ⅱ)|,说明磁耦合作用增强;体系Ⅰ与Ⅱ相比,X由FeⅢ变成CoⅢ,M不变,桥氧原子Ob和Ob2(Ob′2)上的自旋密度增大,进一步从相关BS态的磁轨道比较得出,体系Ⅱ中轨道重叠程度大于体系Ⅰ,结果使X-M之间的反铁磁耦合作用加强.

The magnetic exchange interactions for the biheteroatom 11-heteropoly complexes ： [M（H2O）XW11O39]7-（X=Fe^Ⅲ, Co^Ⅲ; M=Co^Ⅱ） were investigated via density functional theory combined with broken-symmetry approach（DFT-BS） method. The calculated J values are - 35 cm^- 1 （ Ⅰ ） and - 44 cm^- 1 （ Ⅱ ）, respectively, which show that antiferromagnetie exchange interactions exist in these complexes. The order of the absolute value of J is ： ｜ J（ I ） ｜ 〈 ｜ J（ Ⅱ ） ｜ , indicating the increase of coupling interaction from system Ⅰ to Ⅱ. With the change of the heteroatom X via Fe^Ⅱ （ Ⅰ ）→Co^Ⅲ （ Ⅱ ）, the spin densities on bridge oxygen atoms Ob and Ob2 （O＇b2） increase. Furthermore, from the comparison of BS magnetic orbitals in system Ⅰ and Ⅱ we find the overlap of relative orbitals in system Ⅱ enlarges. Consequently, a stronger antiferromagnetic coupling arises in system Ⅱ than in Ⅰ.