Polásek Miloslav, Kotek Jan, Hermann Petr, Císarová Ivana, Binnemans Koen, Lukes Ivan
Department of Inorganic Chemistry, Charles University, Hlavova 2030, 128 40 Prague 2, Czech Republic.
Inorg Chem. 2009 Jan 19;48(2):466-75. doi: 10.1021/ic801597z.
The replacement of one of the acetate pendant arms with a 2-methylpyridine-N-oxide group in the molecule of H4dota significantly alters the coordination properties of the ligand in Ln(III) complexes. The structural properties of the complexes are investigated both in solution and in the solid state. The variable-temperature 1H NMR spectra of Nd(III), Eu(III), and Yb(III) complexes show that the twisted-square-antiprismatic (TSA) isomer is strongly destabilized and suppressed in solution and the complexes exist mostly as the square-antiprismatic (SA) isomers (98% for Eu(III) at -35 degrees C). The exchange between the TSA and SA isomers is fast at room temperature compared to that of the NMR time scale. The flexibility of the six-membered chelate ring formed by coordination of the 2-methylpyridine-N-oxide group to the central ion allows two orientations of this pendant arm relative to the acetate arms: syn-SA (pyridine in the direction of the acetates) and anti-SA (pyridine opposite to the acetates). The syn-SA form was found in the X-ray structure of the Nd(III) complex; the anti-SA forms were found in the structures of Dy(III), Tm(III), and Yb(III) complexes. The UV-vis and 1H NMR spectra of the Eu(III) complex suggest that both forms are in dynamic equilibrium in solution. A derivatization of the pyridine-N-oxide group with a carboxylic group in the 4 position has no significant effect on the properties of the Ln(III) complexes.
在H4dota分子中，将一个乙酸酯侧链臂替换为2-甲基吡啶-N-氧化物基团，会显著改变配体在Ln(III)配合物中的配位性质。对配合物的结构性质在溶液和固态状态下均进行了研究。Nd(III)、Eu(III)和Yb(III)配合物的变温1H NMR谱表明，扭曲四方反棱柱（TSA）异构体在溶液中强烈失稳并受到抑制，配合物主要以四方反棱柱（SA）异构体形式存在（-35℃时Eu(III)的SA异构体占98%）。与NMR时间尺度相比，TSA和SA异构体之间的交换在室温下很快。由2-甲基吡啶-N-氧化物基团与中心离子配位形成的六元螯合环的灵活性，使得该侧链臂相对于乙酸酯侧链臂有两种取向：顺式-SA（吡啶朝向乙酸酯方向）和反式-SA（吡啶与乙酸酯方向相反）。在Nd(III)配合物的X射线结构中发现了顺式-SA形式；在Dy(III)、Tm(III)和Yb(III)配合物的结构中发现了反式-SA形式。Eu(III)配合物的紫外可见光谱和1H NMR谱表明，两种形式在溶液中处于动态平衡。吡啶-N-氧化物基团在4位用羧基进行衍生化，对Ln(III)配合物的性质没有显著影响。
