A series of asymmetric, homoleptic Fe(II) compounds based on the facially-binding tridentate ligand N-methyl-1,1-di(pyridin-2-yl)C_n-amine (LC_n) (C_n = butyl, hexyl, octyl, decyl, dodecyl, tetradecyl and hexadecyl alkyl chains) with formula [Fe^II(LC_n)₂](X)₂·solvate, where n = 4, 14 and X = BF₄ (1C₄ and 1C₁₄) or n = 6, 8, 10, 12, 16 and X = CF₃SO₃ (1C₆–1C₁₂ and 1C₁₆), are reported. Complexes 1C₆ to 1C₁₆ pack in crystalline bilayers in the solid state, forming hydrophobic and hydrophilic regions between adjacent layers of complexes. The combination of short Fe–N bond distances (∼2.00 Å) and SQUID magnetic susceptibility measurements show that the complexes are in the low-spin state across all measured temperature ranges. Differential scanning calorimetry confirmed phase transitions occur in compounds 1C₆, 1C₁₂, 1C₁₄ and 1C₁₆ upon heating from room temperature. The lack of any spin transitions and thermal stability conferred by thermogravimetric analysis over this temperature range suggest that these transitions are crystallographic in nature. ¹H NMR studies show that the low-spin Fe(II) centres undergo partial conversion to paramagnetic species in solution. UV-vis spectroscopy in a range of common organic solvents show that the central Fe ions remain in the +2 oxidation state, suggesting that the increase in magnetic susceptibility in solution is likely due to partial spin-crossover, or due to speciation, in which a proportion of the compounds are high-spin Fe(II) complexes.

中文翻译：

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具有烷基链取代基的同源低自旋 Fe（II） 化合物中的结晶双层形成


一系列基于表面结合的三齿配体 N-甲基-1,1-二（吡啶-2-基）C_n-胺 （LC_n）（C_n = 丁基、己基、辛基、癸基、十二烷基、十四烷基和十六烷基烷基链）的不对称同源 Fe（II） 化合物，分子式为 [Fe^II（LC_n）₂]（X）₂·溶剂化物，其中报道了 n = 4、14 和 X = BF₄（1C₄ 和 1C₁₄）或 n = 6、8、10、12、16 和 X = CF₃SO₃（1C₆–1C₁₂ 和 1C₁₆）。复合物 1C₆ 至 1C₁₆ 在固态的结晶双层中堆积，在复合物的相邻层之间形成疏水和亲水区域。短 Fe-N 键距离 （∼2.00 Å） 和 SQUID 磁化率测量相结合，表明复合物在所有测量温度范围内都处于低自旋状态。差示扫描量热法证实，化合物 1C₆、1C₁₂、1C₁₄ 和 1C₁₆ 在室温加热时发生相变。在此温度范围内，热重分析没有赋予任何自旋转变和热稳定性，这表明这些转变本质上是晶体学的。 ¹H NMR 研究表明，低自旋 Fe（II） 中心在溶液中部分转化为顺磁性物质。在一系列常见有机溶剂中的紫外-可见光谱显示，中心铁离子保持 +2 氧化态，这表明溶液中磁化率的增加可能是由于部分自旋交叉，或由于物种形成，其中一部分化合物是高自旋 Fe（II） 络合物。