Coordination of Lead(II) in the Supramolecular Environment Provided by a 鈥淭wo-Story鈥?Calix[6]arene-based N6 Ligand

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• 作者：Diana Over ; Xianshun Zeng ; Claudia Bornholdt ; J茅r么me Marrot ; Olivia Reinaud
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：December 16, 2013
• 年：2013
• 卷：52
• 期：24
• 页码：14089-14095
• 全文大小：432K
• 年卷期：v.52,no.24(December 16, 2013)
• ISSN：1520-510X

文摘

First insights into the coordination properties and host鈥揼uest behavior of a 鈥渢wo story鈥?calix[6]aza-cryptand (1) are described. The ligand is constituted of a triazacyclononane (TACN) cap and three pyridine (PY) spacers connected to the calix[6]arene small rim. The resulting N₆ donor site coordinates Pb^II ions to give complexes that are highly stable. X-ray diffraction structures reveal a hemidirected environment for Pb^II with strong coordination to the TACN cap and weaker bonds with the three PY residues. A guest molecule, either water or EtOH, sitting in the calixarene macrocycle and hydrogen-bonded to the phenoxyl units at the level of the small rim further stabilizes the complexes through electrostatic interactions with the metal center and the calixarene core. In-depth ¹H NMR studies confirm the host鈥揼uest behavior of the complexes in solution, with evidence of embedment of neutral guest molecules such as EtOH, BuOH, and N-Me-formamide. Hence, in spite of the presence of a N₆ donor, the calixarene macrocycle can be open to guest interaction, giving rise to seven-coordinate dicationic complexes. Noteworthy also is the flexibility of the macrocycle that allows Pb^II to adopt its preferred hemidirected environment in spite of the three covalent links connecting the calixarene core to the three PY groups. The flexibility of the system is further illustrated by the possible coordination of an exogenous anionic ligand in the exo position. Hence, compared to the previously described 鈥渙ne story鈥?calix[6]aza-cryptands, ligand 1 displays several similar but also new features that are discussed.