In order to develop novel, more efficient, and/or selective contrast agents for magnetic resonance imaging (MRI), different modi operandi are explored as alternatives to water-relaxation enhancement. In this work, cobalt(II/III) complexes of bis(N-trifluoroethyl)cyclam derivatives with two acetate or two phosphonate pendant arms, H₂te2f2a and H₄te2f2p, were prepared and investigated. X-ray diffraction structures confirmed octahedral coordination with a very stable trans-III cyclam conformation and with fluorine atoms located about 5.3 Å from the metal center. The Co(II) complexes are kinetically inert, decomposing slowly even in 1 M aqueous HCl at 80 °C. The Co(II) complexes exhibited well-resolved paramagnetically shifted NMR spectra. These were interpreted with the help of quantum chemistry calculations. The ¹³C NMR shifts of the trans-[Co^II(te2f2p)]²⁻ complex were successfully assigned based on spin density delocalization within the ligand molecule. The obtained spin density also helps to describe d-metal-induced NMR relaxation properties of ¹⁹F nuclei, including the contribution of a Fermi contact relaxation mechanism. The paramagnetic complexes show convenient relaxation properties to be used as ¹⁹F MRI contrast agents.

中文翻译：

---

具有Cyclam衍生物的顺磁性钴（II）配合物：朝向19F MRI造影剂。

为了开发用于磁共振成像（MRI）的新颖，更有效和/或选择性的造影剂，人们探索了不同的操作方法作为水松弛增强的替代方法。在这项工作中，制备并研究了双（N-三氟乙基）环酰胺衍生物与两个乙酸酯或两个膦酸酯侧链H ₂ te2f2a和H ₄ te2f2p的钴（II / III）配合物。X射线衍射结构，证实了一个非常稳定的八面体配位反式- IIICyclam构象，氟原子距离金属中心约5.3Å。Co（II）络合物具有动力学惰性，即使在80°C的1 M HCl水溶液中也能缓慢分解。Co（II）配合物表现出很好解析的顺磁位移NMR光谱。这些是借助量子化学计算来解释的。基于配体分子内的自旋密度离域，成功地分配了反式-[Co ^II（te2f2p）] ^2-的¹³ C NMR位移。获得的自旋密度还有助于描述^19的d-金属诱导的NMR弛豫特性F核，包括费米接触弛豫机制的贡献。顺磁性复合物显示出方便的弛豫特性，可用作¹⁹ F MRI造影剂。