Theoretical Modeling of the Magnetic Behavior of Thiacalix[4]arene Tetranuclear Mn^II₂Gd^III₂ and Co^II₂Eu^III₂ Complexes

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 χ<i>T</i> 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 (<i>J</i>(Mn, Mn) = −1.6 cm^–1, <i>J</i>_s(Mn, Gd) = 0.8 cm^–1, <i>g</i> = 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 χ<i>T</i> versus <i>T</i> 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 (<i>D</i> = 20.5 cm^–1, <i>J</i> = −0.4 cm^–1, <i>g</i>_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

A new member of the cationic dinitrosyl iron complexes family incorporating N-ethylthiourea is effective against human HeLa and MCF-7 tumor cell lines

<p>A new analog of the active site of mononuclear dinitrosyl [1Fe–2S] proteins, [C₃N₂H₈SFe(NO)₂Cl][Fe(NO)₂(C₃N₂H₈S)₂]⁺Cl⁻ (<b>I</b>), has been synthesized by reacting NO with an aqueous mixture of iron(II) sulfate and N-ethylthiourea in acidic medium. The structure and properties of the complex were studied by X-ray diffraction, IR, Mössbauer, and EPR spectroscopy, in addition to quantum chemical calculations. Complex <b>I</b> spontaneously generates NO in protic media. The cytotoxicity of <b>I</b> was investigated against human cervical carcinoma (HeLa), breast cancer (MCF7), and non-immortalized (FetMCS) cell lines. The cytotoxicity of <b>I</b> against HeLa is similar to that of anticancer agents currently used clinically (platinum complexes), but <b>I</b> is 10 times less toxic in normal cells. The cytotoxicity of MCF7 cells to <b>I</b> is low.</p