Laboratoire de Chimie et de Biochimie Pharmacologiques et Toxicologiques, Université Paris Descartes, PRES Sorbonne Paris Cité, CNRS UMR 8601 , 45 rue des Saints Pères, 75006 Paris, France.
Inorg Chem. 2013 Dec 16;52(24):14089-95. doi: 10.1021/ic4018486. Epub 2013 Nov 20.
First insights into the coordination properties and host-guest behavior of a "two story" 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 (1)H NMR studies confirm the host-guest 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 "one story" calix[6]aza-cryptands, ligand 1 displays several similar but also new features that are discussed.
描述了“两层”杯[6]氮杂冠醚（1）的配位性质和主体客体行为的初步见解。该配体由三氮杂环壬烷（TACN）帽和连接到杯[6]芳烃小边缘的三个吡啶（PY）间隔物组成。由此产生的 N6 供体位点与 Pb(II) 离子配位，得到高度稳定的配合物。X 射线衍射结构显示 Pb(II) 的半直接环境，与 TACN 帽强烈配位，与三个 PY 残基的键较弱。位于杯芳烃大环内的客体分子（无论是水还是 EtOH）与小边缘处的苯氧基单元形成氢键，通过与金属中心和杯芳烃核的静电相互作用进一步稳定配合物。深入的（1）H NMR 研究证实了配合物在溶液中的主体客体行为，有证据表明中性客体分子如 EtOH、BuOH 和 N-Me-甲酰胺嵌入。因此，尽管存在 N6 供体，杯芳烃大环仍可与客体相互作用，形成七配位的二价阳离子配合物。值得注意的是，大环的灵活性允许 Pb(II) 采用其首选的半直接环境，尽管连接杯芳烃核与三个 PY 基团的有三个共价键。该系统的灵活性还通过在外部位点可能配位外源阴离子配体进一步说明。因此，与以前描述的“单层”杯[6]氮杂冠醚相比，配体 1 显示出几个相似但也有新的特征，这些特征将进行讨论。
