The hydrate of a neutral iron(III) complex based on the pyruvic acid thiosemicarbazone ligand [Fe^III(Hthpy)(thpy)]·H₂O (1) was synthesized and characterized using FT-IR spectroscopy, powder and single-crystal X-ray diffraction, dc magnetic measurements, EPR and ⁵⁷Fe Mössbauer spectroscopy. The crystal structure of 1 was determined for the first time. Two distinct chelating ligands Hthpy⁻ and thpy²⁻ coordinate the Fe(III) ion to form the FeN₂O₂S₂ octahedron which shows a low spin geometry at 150–350 K. The crystal packing contains infinite chains of the Fe(III) complexes as well as water molecules located in cavities. Along the chain, π–π interacting pairs of the Fe complexes are linked by H-bonding. According to the dc magnetic measurements, the complete abrupt spin-crossover with half-transition temperature T_1/2 = 340 K and a hysteresis loop of 45 K occurs in the temperature range of 300–363 K. Based on the X-ray structure of 1, the Bleaney–Bowers equation for the isolated dimer model was used to approximate the temperature dependence of the magnetic susceptibility in the range of 2–50 K. The defined intradimer exchange constant J_exp = −0.498(1) K corresponds to a weak antiferromagnetic exchange between the iron(III) magnetic centers. DFT calculations of H- and π–π bonded fragments of the crystal structure of 1 in the HS and LS states were carried out. Moreover, BS-DFT calculations confirm the presence of antiferromagnetic exchange J_calc = −0.92 K in the π–π bonded pairs of the ferric complexes and show the exchange pathway between Fe(III) ions by the calculated spin density distribution.

中文翻译：

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基于丙酮酸硫代氨基脲配体的中性铁 （III） 络合物的水合物，具有 T1/2 = 340 K 的突然自旋交叉和 45 K 的宽磁滞回线


基于丙酮酸硫代氨基脲配体 [Fe^III（Hthpy）（thpy）]的中性铁 （III） 络合物的水合物使用 FT-IR 光谱、粉末和单晶 X 射线衍射、直流磁测量、EPR 和 ⁵⁷Fe Mössbauer 光谱合成和表征 H₂O （1）。首次测定 1 的晶体结构。两种不同的螯合配体 Hthpy⁻ 和 thpy²⁻ 使 Fe（III） 离子配位形成 FeN₂O₂S₂ 八面体，它在 150-350 K 时显示出低自旋几何形状。晶体填充包含 Fe（III） 络合物的无限链以及位于空腔中的水分子。沿着链，π-π 对相互作用的 Fe 配合物通过 H 键连接。根据直流磁测量，在 300-363 K 的温度范围内，会出现半转变温度 T_1/2 = 340 K 且磁滞回线为 45 K 的完全突变自旋交叉。基于 1 的 X 射线结构，使用隔离二聚体模型的 Bleaney-Bowers 方程来近似 2-50 K 范围内磁化率的温度依赖性。定义的二聚体内交换常数 J_exp = −0.498（1） K 对应于铁 （III） 磁心之间的弱反铁磁交换。对 HS 和 LS 状态下 1 晶体结构的 H 和 π-π 键合碎片进行 DFT 计算。 此外，BS-DFT 计算证实了铁络合物的 π-π 键合对中存在反铁磁交换 J_calc = −0.92 K，并通过计算的自旋密度分布显示了 Fe（III） 离子之间的交换途径。