Combined NMR, DFT and X-ray studies highlight structural and hydration changes of [Ln(AAZTA)]- complexes across the series
Combined NMR, DFT and X-ray studies highlight structural and hydration changes of [Ln(AAZTA)]- complexes across the series
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DOI：
10.1039/c9qi01442j
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发表时间：
2020-02-07
影响因子：
7
通讯作者：
Botta, Mauro
中科院分区：
文献类型：
--
作者：
Baranyas, Zsolt;Castetli, Daniela Delti;Botta, Mauro
我们用实验和理论相结合的方法对[Ln(AAZTA)](-)配合物进行了详细的结构研究。对整个系列甲基峰的H-1核磁共振顺磁位移的分析表明，Ho和Er之间发生了结构变化。用化学交换饱和转移实验确定了在278K时配位水分子的数目和相应的交换率k(Ex)。对Ho(III)络合物的Z-谱记录了两个信号，证实了两个配位水分子的存在，它们具有相当不同的交换率：5.8(+/-3.0)×10(3)和8.1(+/-0.5)×10(4)S(-1)。相反，Er(III)和Tm(III)配合物在Z谱中呈现单一信号。从Gd(III)到Yb(III)，配位水分子(S)的交换率明显降低。密度泛函理论计算支持稀土系列末端水化数的变化，这是配位水分子周围空间压缩增加的结果，减小了金属离子的尺寸。对Er(III)配合物的X-射线衍射谱研究证实，Er(III)配合物中存在单一的内球水分子和金属离子的十二面体配位环境。
We report a detailed structural study of [Ln(AAZTA)](-) complexes by using a combination of experimental and theoretical tools. The analysis of the H-1 NMR paramagnetic shift of the methyl peak across the series suggests that a structural change occurs between Ho and Er. Chemical exchange saturation transfer experiments were subsequently used to determine the number of coordinated water molecules and their corresponding exchange rates k(ex) at 278 K. The Z-spectra recorded for the Ho(iii) complex present two signals that confirm the presence of two coordinated water molecules, which are endowed with rather different exchange rates: 5.8(+/- 3.0) x 10(3) and 8.1(+/- 0.5) x 10(4) s(-1). On the contrary, the Er(iii) and Tm(iii) complexes present a single signal in the Z-spectra. The exchange rate of the coordinated water molecule(s) decreases markedly across the series from Gd(iii) to Yb(iii). DFT calculations support the change in hydration number by the end of the lanthanide series, which is the result of an increased steric compression around one of the coordinated water molecules on decreasing the size of the metal ion. X-ray diffraction studies on the Er(iii) complex confirm the presence of a single inner-sphere water molecule and the dodecahedral coordination environment of the metal ion.