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

Sergey M. Aldoshin, Nataliya A. Sanina, Andrew V. Palii, Boris S. Tsukerblat

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Abstract

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 MnII2GdIII2 and CoII2EuIII2. The energy pattern of the MnII2GdIII2 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 MnII2GdIII2 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, Js(Mn, Gd) = 0.8 cm-1, g = 1.97). The model for the CoII2EuIII2 complex includes uniaxial anisotropy of the seven-coordinate CoII ions and an isotropic exchange interaction in the CoII2 pair, while the EuIII 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 CoII ions) dominates (weak-exchange limit) in the CoII2EuIII2 complex (D = 20.5 cm-1, J = -0.4 cm-1, gCo = 2.22). This complex is concluded to exhibit an easy plane of magnetization (arising from the CoII 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 CoII2 pair in the weak-exchange limit.

Original languageEnglish
Pages (from-to)3566-3575
Number of pages10
JournalInorganic Chemistry
Volume55
Issue number7
DOIs
StatePublished - 18 Apr 2016

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