密度泛函理论研究稀土配合物的磁学性质:Y~Ⅲ-,Gd~Ⅲ-氮氧自由基配合物磁耦合机理

Density functional theory study on magnetic properties of rare-earth complexes:magnetic coupling mechanism in Y~Ⅲ and Gd~Ⅲ complexes with nitronyl nitroxide

应用密度泛函理论结合对称性破损方法(DFT-BS)研究了YⅢ-,GdⅢ-氮氧自由基配合物,Ln(hfac)3(NITPhOCH3)2(Ln=YⅢ1,GdⅢ2,hafc=hexafluoroacetylaceto-nate)(NITPhOCH3=4′-methoxyo-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxi-de).这两个配合物的中心离子分别是抗磁性的YⅢ和顺磁性的GdⅢ.它们各自被两个氮氧自由基配位,形成一个两自旋中心和一个三自旋中心的磁性分子体系.分子磁轨道分析显示,在这两个配合物的氮氧自由基之间的反铁磁耦合作用中,YⅢ和GdⅢ离子空的4d/5d轨道扮演了磁耦合的传递作用.对于GdⅢ和自由基配体之间的铁磁耦合作用,通过半充满的4f壳层和自由基的NO(π*)局域磁轨道的重叠积分计算显示,它们之间的轨道重叠非常小.磁轨道分析和自旋布居分析也显示GdⅢ收缩的4f7轨道和NO(π*)局域磁轨道都相当定域,所以我们认为这种铁磁性耦合主要是由于GdⅢ的4f7轨道与NO(π*)局域磁轨道近乎完全定域的结果.

For two model magnetic systems, based on novel rare-earth organic radical complexes Ln（hfac）3（NITPhOCH3）2 （Ln=Y^III1, Gd^III2, hafc = hexafluoroacetylacetonate） （NITPhOCH3 = 4＂-methoxyo-phenyl-4,4,5,5-tetramethylimi-dazoline-l-oxyl-3-oxide）, the magnetic properties of the nitronyl nitroxide radicals bound to diamagnetic （Y^III） and paramagnetic （Gdnl） rare-earth ions were investigated by density functional theory （DFT）. The magnetic coupling mechanisms were also explored in the viewpoint of magnetic molecular orbital and spin density populations. The DFT calculations show that the empty 4d-orbital of Y^III and 5d-orbital of Gd^III play an important role in the antiferromagnetic coupling between the two nitronyl nitroxide radical ligands, and that the ferromagnetic coupling between the Gd^III ion and the radical magnetic centers can be attributed to the nearly complete localization of isotropic 4f-shell and singly occupied magnetic orbital （π＊） of the nitronyl nitroxide.