三价镧锕离子与三种18-冠-6配体的络合行为
Complexation Behavior of Trivalent Lanthanide/Actinide With Three 18-Crown-6 Ligands
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摘要: 冠醚是一类重要的主体化合物，在超分子识别、金属离子分离等领域有重要应用。冠醚环上取代基的种类和数量会影响冠醚结构，进而影响其与金属离子的络合能力。利用紫外光谱、微量热等手段，研究了三价镧系离子与结构渐变的三种18-冠-6化合物在乙腈中的络合行为，考察了冠醚环上苯基取代基对络合反应的影响。研究结果表明：Nd3+与三种冠醚均形成1∶1配合物，络合反应吸热，反应由熵驱动；冠醚环上的苯基取代基使得冠醚与Nd3+的络合能力减弱。并基于密度泛函理论优化了Nd3+及Am3+与三种冠醚化合物形成的配合物结构，计算了其生成吉布斯自由能，结果表明，Nd3+比Am3+与含氧供体冠醚的络合能力略强，这可能主要源自两种离子间的微小尺寸差别，使得Nd3+与冠醚产生更好的尺寸匹配效应。Abstract: Crown ethers are a group of important host compounds that receive vast applications in areas such as supramolecular recognition and metal separation. The substituents on crown ethers are expected to have great impacts on the complexation ability to metal ions by crown ethers. In this work, the complexation of three structurally related 18-crown-6 ligands with Nd3+ in acetonitrile was experimentally studied through UV-Vis spectroscopy and microcalorimetry. The impact of phenyl group attached to the crown ethers on the complexation was evaluated. The results indicate that all the three crown ethers form 1∶1 complex with Nd3+. The complexation reaction is driven by positive entropies but opposed by endothermic enthalpies. The phenyl group lowers the complexation ability of crown ethers to Nd3+. Moreover, the complexation behavior of Nd3+ and Am3+ with the three crown ethers was compared through DFT calculations. Nd3+ is found to exhibit slightly stronger interactions with the same crown ether than Am3+, which may be attributed to the slight difference in ionic size between Nd3+ and Am3+ that enables more favorable size match of Nd3+ with the crown ethers.
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Keywords:
- crown ether /
- lanthanides /
- actinides /
- complexation /
- thermodynamics
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