2 research outputs found
Theoretical Modeling of the Magnetic Behavior of Thiacalix[4]arene Tetranuclear Mn<sup>II</sup><sub>2</sub>Gd<sup>III</sup><sub>2</sub> and Co<sup>II</sup><sub>2</sub>Eu<sup>III</sup><sub>2</sub> Complexes
In
view of a wide perspective of 3dā4f complexes in single-molecule
magnetism, here we propose an explanation of the magnetic behavior
of the two thiacalix[4]Āarene tetranuclear heterometallic complexes
Mn<sup>II</sup><sub>2</sub>Gd<sup>III</sup><sub>2</sub> and Co<sup>II</sup><sub>2</sub>Eu<sup>III</sup><sub>2</sub>. The energy pattern
of the Mn<sup>II</sup><sub>2</sub>Gd<sup>III</sup><sub>2</sub> complex
evaluated in the framework of the isotropic exchange model exhibits
a rotational band of the low-lying spin excitations within which the
LandeĢ intervals are affected by the biquadratic spināspin
interactions. The nonmonotonic temperature dependence of the Ļ<i>T</i> product observed for the Mn<sup>II</sup><sub>2</sub>Gd<sup>III</sup><sub>2</sub> complex is attributed to the competitive influence
of the ferromagnetic MnāGd and antiferromagnetic MnāMn
exchange interactions, the latter being stronger (<i>J</i>(Mn, Mn) = ā1.6 cm<sup>ā1</sup>, <i>J</i><sub>s</sub>(Mn, Gd) = 0.8 cm<sup>ā1</sup>, <i>g</i> = 1.97). The model for the Co<sup>II</sup><sub>2</sub>Eu<sup>III</sup><sub>2</sub> complex includes uniaxial anisotropy of the seven-coordinate
Co<sup>II</sup> ions and an isotropic exchange interaction in the
Co<sup>II</sup><sub>2</sub> pair, while the Eu<sup>III</sup> ions
are diamagnetic in their ground states. Best-fit analysis of Ļ<i>T</i> versus <i>T</i> showed that the anisotropic
contribution (arising from a large zero-field splitting in Co<sup>II</sup> ions) dominates (weak-exchange limit) in the Co<sup>II</sup><sub>2</sub>Eu<sup>III</sup><sub>2</sub> complex (<i>D</i> = 20.5 cm<sup>ā1</sup>, <i>J</i> = ā0.4
cm<sup>ā1</sup>, <i>g</i><sub>Co</sub> = 2.22). This
complex is concluded to exhibit an easy plane of magnetization (arising
from the Co<sup>II</sup> pair). It is shown that the low-lying part
of the spectrum can be described by a highly anisotropic effective
spin-<sup>1</sup>/<sub>2</sub> Hamiltonian that is deduced for the
Co<sup>II</sup><sub>2</sub> pair in the weak-exchange limit
Single-Ion Magnet Et<sub>4</sub>N[Co<sup>II</sup>(hfac)<sub>3</sub>] with Nonuniaxial Anisotropy: Synthesis, Experimental Characterization, and Theoretical Modeling
In
this article we report the synthesis and structure of the new
CoĀ(II) complex Et<sub>4</sub>NĀ[Co<sup>II</sup>Ā(hfac)<sub>3</sub>] (<b>I</b>) (hfac = hexafluoroacetylacetonate) exhibiting
single-ion magnet (SIM) behavior. The performed analysis of the magnetic
characteristics based on the complementary experimental techniques
such as static and dynamic magnetic measurements, electron paramagnetic
resonance spectroscopy in conjunction with the theoretical modeling
(parametric Hamiltonian and ab initio calculations) demonstrates that
the SIM properties of <b>I</b> arise from the nonuniaxial magnetic
anisotropy with strong positive axial and significant rhombic contributions