Theoretical Modeling of the Magnetic Behavior of Thiacalix[4]arene Tetranuclear MnII2GdIII2 and CoII2EuIII2 Complexes

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• 作者：Sergey M. Aldoshin ; Nataliya A. Sanina ; Andrew V. Palii ; Boris S. Tsukerblat
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：April 4, 2016
• 年：2016
• 卷：55
• 期：7
• 页码：3566-3575
• 全文大小：443K
• ISSN：1520-510X

文摘

In view of a wide perspective of 3d–4f complexes in single-molecule magnetism, here we propose an explanation of the magnetic behavior of the two thiacalix[4]arene tetranuclear heterometallic complexes Mn^II₂Gd^III₂ and Co^II₂Eu^III₂. The energy pattern of the Mn^II₂Gd^III₂ complex evaluated in the framework of the isotropic exchange model exhibits a rotational band of the low-lying spin excitations within which the Landé intervals are affected by the biquadratic spin–spin interactions. The nonmonotonic temperature dependence of the χT product observed for the Mn^II₂Gd^III₂ complex is attributed to the competitive influence of the ferromagnetic Mn–Gd and antiferromagnetic Mn–Mn exchange interactions, the latter being stronger (J(Mn, Mn) = −1.6 cm^–1, J_s(Mn, Gd) = 0.8 cm^–1, g = 1.97). The model for the Co^II₂Eu^III₂ complex includes uniaxial anisotropy of the seven-coordinate Co^II ions and an isotropic exchange interaction in the Co^II₂ pair, while the Eu^III ions are diamagnetic in their ground states. Best-fit analysis of χT versus T showed that the anisotropic contribution (arising from a large zero-field splitting in Co^II ions) dominates (weak-exchange limit) in the Co^II₂Eu^III₂ complex (D = 20.5 cm^–1, J = −0.4 cm^–1, g_Co = 2.22). This complex is concluded to exhibit an easy plane of magnetization (arising from the Co^II pair). It is shown that the low-lying part of the spectrum can be described by a highly anisotropic effective spin-¹/₂ Hamiltonian that is deduced for the Co^II₂ pair in the weak-exchange limit.