Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
Dalton Trans. 2011 Nov 7;40(41):10897-906. doi: 10.1039/c1dt10600g. Epub 2011 Aug 15.
Theoretical calculations using density functional methods have been performed on two dinuclear {Ni(II)-Gd(III)} and two trinuclear {Ni(II)-Gd(III)-Ni(II)} complexes having two and three μ-OR (R = alkyl or aromatic groups) bridging groups. The different magnetic behaviour, having moderately strong ferromagnetic coupling for complexes having two μ-OR groups and weak ferromagnetic coupling for complexes having three μ-OR groups, observed experimentally is very well reproduced by the calculations. Additionally, computation of overlap integrals MO and NBO analysis reveals a clear increase in antiferromagnetic contribution to the net exchange for three μ-OR bridged {Ni-Gd} dimers and also provides several important clues regarding the mechanism of magnetic coupling. Besides, MO and NBO analysis discloses the role of the empty 5d orbitals of the Gd(III) ion on the mechanism of magnetic coupling. Magneto-structural correlations for Ni-O-Gd bond angles, Ni-O and Gd-O bond distances, and the Ni-O-Gd-O dihedral angle have been developed and compared with the published experimental {Ni-Gd} structures and their J values indicate that the Ni-O-Gd bond angles play a prominent role in these types of complexes. The computation has then been extended to two trinuclear {Ni(II)-Gd(III)-Ni(II)} complexes and here both the {Ni-Gd} and the {Ni-Ni} interactions have been computed. Our calculations reveal that, for both structures studied, the two {NiGd} interactions are ferromagnetic and are similar in strength. The {Ni-Ni} interaction is antiferromagnetic in nature and our study reveals that its inclusion in fitting the magnetic data is necessary to obtain a reliable set of spin Hamiltonian parameters. Extensive magneto-structural correlations have been developed for the trinuclear complexes and the observed J trend for the trinuclear complex is similar to that of the dinuclear {Ni-Gd} complex. In addition to the structural parameters discussed above, for trinuclear complexes the twist angle between the two Ni-O-Gd planes is also an important parameter which influences the J values.
使用密度泛函方法进行了理论计算，研究了两个双核{Ni(II)-Gd(III)}和两个四核{Ni(II)-Gd(III)-Ni(II)}配合物，它们具有两个和三个μ-OR（R = 烷基或芳香基团）桥联基团。实验中观察到的不同磁行为，具有两个μ-OR 基团的配合物具有中等强度的铁磁耦合，而具有三个μ-OR 基团的配合物具有弱铁磁耦合，这些都可以通过计算很好地重现。此外，计算重叠积分 MO 和 NBO 分析表明，对于三个μ-OR 桥联{Ni-Gd}二聚体，反铁磁贡献对净交换有明显增加，并且还提供了有关磁耦合机制的几个重要线索。此外，MO 和 NBO 分析揭示了 Gd(III)离子的空 5d 轨道对磁耦合机制的作用。已经开发了 Ni-O-Gd 键角、Ni-O 和 Gd-O 键距离以及 Ni-O-Gd-O 二面角的磁结构相关性，并与已发表的实验{Ni-Gd}结构及其 J 值进行了比较，结果表明 Ni-O-Gd 键角在这些类型的配合物中起着重要作用。计算随后扩展到两个四核{Ni(II)-Gd(III)-Ni(II)}配合物，在这里计算了{Ni-Gd}和{Ni-Ni}相互作用。我们的计算表明，对于研究的两种结构，两个{NiGd}相互作用都是铁磁的，强度相似。{Ni-Ni}相互作用是反铁磁的，我们的研究表明，在拟合磁数据时必须包含它，才能获得一组可靠的自旋哈密顿参数。已经为四核配合物开发了广泛的磁结构相关性，并且观察到的四核配合物的 J 趋势与双核{Ni-Gd}配合物的趋势相似。除了上述结构参数外，对于四核配合物，两个 Ni-O-Gd 平面之间的扭曲角也是影响 J 值的重要参数。
