Mössbauer, electron paramagnetic resonance, and magnetic susceptibility studies on members of a new family of cyano-bridged 3d-4f complexes. Demonstration of anisotropic exchange in a Fe-Gd complex.
Mössbauer, electron paramagnetic resonance, and magnetic susceptibility studies on members of a new family of cyano-bridged 3d-4f complexes. Demonstration of anisotropic exchange in a Fe-Gd complex.
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DOI：
10.1021/ic902516r
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发表时间：
2010-04-05
影响因子：
4.6
通讯作者：
Andruh, Marius
中科院分区：
文献类型：
--
作者：
Stoian, Sebastian A.;Paraschiv, Carmen;Kiritsakas, Nathalie;Lloret, Francesc;Munck, Eckard;Bominaar, Emile L.;Andruh, Marius
报道了一个新的M（μ-CN）Ln配合物的合成和晶体学性质。在六亚甲基四胺（hmt）存在下，稀土硝酸盐（LnIII = La，Pr，Nd，Sm，Eu，Gd，Dy，Ho）与K_3 [M（CN）_6]（MIII = Fe，Co）在水中反应，制备了两个结构系列的稀土配合物。第一系列由六个同晶异双核配合物[（CN）5 M-CNLn（H2O）8]·2 hmt（[FeLa] 1，[FePr] 2，[FeNd] 3，[FeSm] 4，[FeEu] 5，[FeGd] 6）组成，第二系列由四个同晶离子配合物[Ln（H2O）8][M（CN）6]·hmt（[FeDy] 7，[FeHo] 8，[CoEu] 9，[CoGd] 10）组成。六亚甲基四胺分子通过参与氢键相互作用的扩展网络而有助于晶体的稳定。在这两个系列中，水配体与来自末端CN基团和hmt分子的氮原子氢键合。[FeGd]配合物已经用57 Fe穆斯堡尔谱、EPR和磁化率测量进行了分析。我们还分析了[FeLa]复合物，其中顺磁性Gd III被反磁性La III取代，以获得有关低自旋FeIII位点的信息，该位点在互补位点处的顺磁性离子的存在下不可访问。出于同样的原因，[CoGd]配合物，含有抗磁性的CoIII，进行了研究与EPR和磁化率测量，证实了S = 7/2自旋的Gd III。关于[FeGd]中的顺磁性位点的先前知识允许详细分析它们之间的交换相互作用。特别是，在[FeGd]交换相互作用是否是各向同性或各向异性的问题已经解决。标准变温磁化率测量仅提供Jx、Jy和Jz的线性组合的值，但不包含关于各个交换参数Jx、Jy和Jz的值的信息。与此相反，自旋哈密顿分析的可变场，变温穆斯堡尔谱揭示了一个精致的各向异性交换参数的敏感性。对这些依赖性的分析，结合采用[FeLa]获得的g值，得出值Jx =<$1· J ·<$2 +0.11 cm−1，Jy = +0.33 cm−1，Jz = +1.20 cm−1（惯例）。分析了这些结果与磁化率数据的一致性。交换各向异性是植根于低自旋Fe III离子的空间各向异性。各向异性交换的条件是在铁位点存在低位轨道激发态，其（i）通过与轨道基态的自旋-轨道耦合有效地相互作用，以及（ii）与Gd位点具有不同于基态的值的交换参数。无自旋-轨道耦合的DFT计算表明，FeIII离子的t2 g5基态构型的未成对电子占据xy轨道，即沿着垂直于Fe → Gd矢量的平面的轨道。交换耦合常数为这个轨道，jxy，和其他t2 g轨道，jyz和jxz，已被确定使用的理论模型，将它们与各向异性交换参数和Fe III的g值。得到的值jyz = −5.7 cm−1、jxz = −4.9 cm−1和jxy = +0.3 cm−1是完全不同的。本文简要地讨论了这种差异的起源。
The synthesis and crystallographic characterization of a new family of M(μ-CN)Ln complexes are reported. Two structural series have been prepared by reacting in water rare earth nitrates (LnIII = La, Pr, Nd, Sm, Eu, Gd, Dy, Ho) with K3[M(CN)6] (MIII = Fe, Co) in the presence of hexamethylenetetramine (hmt). The first series consists of six isomorphous heterobinuclear complexes, [(CN)5M-CNLn(H2O)8]·2hmt ([FeLa] 1, [FePr] 2, [FeNd] 3, [FeSm] 4, [FeEu] 5, [FeGd] 6), while the second series consists of four isostructural ionic complexes, [Ln(H2O)8][M(CN)6]·hmt ([FeDy] 7, [FeHo] 8, [CoEu] 9, [CoGd] 10). The hexamethylenetetramine molecules contribute to the stabilization of the crystals by participating in an extended network of hydrogen bond interactions. In both series the aqua ligands are hydrogen bonded to the nitrogen atoms from both the terminal CN groups and the hmt molecules. The [FeGd] complex has been analyzed with 57Fe Mössbauer spectroscopy, EPR, and magnetic susceptibility measurements. We have also analyzed the [FeLa] complex, in which the paramagnetic GdIII is replaced by diamagnetic LaIII, to obtain information about the low-spin FeIII site that is not accessible in the presence of a paramagnetic ion at the complementary site. For the same reason, the [CoGd] complex, containing diamagnetic CoIII, was studied with EPR and magnetic susceptibility measurements, which confirmed the S = 7/2 spin of GdIII. Prior knowledge about the paramagnetic sites in [FeGd] allows a detailed analysis of the exchange interactions between them. In particular, the question of whether the exchange interaction in [FeGd] is isotropic or anisotropic has been addressed. Standard variable-temperature magnetic susceptibility measurements provide only the value for a linear combination of Jx, Jy, and Jz but contain no information about the values of the individual exchange parameters Jx, Jy, and Jz. In contrast, the spin-Hamiltonian analysis of the variable-field, variable-temperature Mössbauer spectra reveals an exquisite sensitivity on the anisotropic exchange parameters. Analysis of these dependencies in conjunction with adopting the g-values obtained for [FeLa], yielded the values Jx = Ŝ1 · J · Ŝ2 +0.11 cm−1, Jy = +0.33 cm−1, and Jz = +1.20 cm−1 (convention). The consistency of these results with magnetic susceptibility data is analyzed. The exchange anisotropy is rooted in the spatial anisotropy of the low-spin FeIII ion. The condition for anisotropic exchange is the presence of low-lying orbital excited states at the ferric site that (i) effectively interact through spin-orbit coupling with the orbital ground state and (ii) have an exchange parameter with the Gd site with a value different from that for the ground state. DFT calculations, without spin-orbit coupling, reveal that the unpaired electron of the t2g5 ground configuration of the FeIII ion occupies the xy orbital, i.e. the orbital along the plane perpendicular to the Fe⋯Gd vector. The exchange-coupling constants for this orbital, jxy, and the other t2g orbitals, jyz and jxz, have been determined using a theoretical model that relates them to the anisotropic exchange parameters and the g-values of FeIII. The resulting values, jyz = −5.7 cm−1, jxz = −4.9 cm−1, and jxy = +0.3 cm−1 are quite different. The origin of the difference is briefly discussed.
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影响因子：
2.7
作者：
BARTOLOME, F;BARTOLOME, J;KAHN, O
通讯作者：
KAHN, O
影响因子：
4.6
作者：
BENELLI, C;CANESCHI, A;PARDI, L
通讯作者：
PARDI, L
影响因子：
15
作者：
ANDRUH, M;RAMADE, I;TROMBE, JC
通讯作者：
TROMBE, JC
DOI：
10.1088/0370-1301/69/12/304
发表时间：
1956-01-01
期刊：
PROCEEDINGS OF THE PHYSICAL SOCIETY OF LONDON SECTION B
影响因子：
--
作者：
BAKER, JM;BLEANEY, B;BOWERS, KD
通讯作者：
BOWERS, KD
影响因子：
1.7
作者：
BENCINI, A;GATTESCHI, D
通讯作者：
GATTESCHI, D