Self-assembly of L-cysteinato trinuclear cations into metallosupramolecular architectures controlled by protons, metal ions, and chirality
Self-assembly of L-cysteinato trinuclear cations into metallosupramolecular architectures controlled by protons, metal ions, and chirality
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DOI：
10.1002/chem.200800887
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发表时间：
2008-01-01
影响因子：
4.3
通讯作者：
Konno, Takumi
中科院分区：
文献类型：
--
作者：
Aridomi, Takashi;Takamura, Keiichi;Konno, Takumi
在过去的十年中，金属超分子结构如配位环、笼和管等因其结构特点和潜在的应用而引起了广泛的关注，其中包括小分子和离子的识别和包涵。[1,2]在许多情况下，金属超分子是通过金属辅助组装有机分子与几个金属结合位点[1]来合成的，从而形成热力学稳定的组装结构。另一方面，由一种构建块的自组装产生的金属超分子物种的例子相对较少，尽管这种方法有利于由外部因素可逆控制组装和拆卸结构。实现这一目标的一种方法是在金属中心设计具有空受体位点的配位化合物，以及响应外部因素与另一个金属中心结合的自由供体基团。具有游离羧基的汞（II）配位化合物是创建可逆自组装体系的潜在候选物，因为1)汞（II）离子可以采用几种配位几何，如二配位线性、三配位t形和四配位四面体；2)汞（II）离子不仅对软硫供体有很好的亲和性，而且对硬氧供体也有很好的亲和性；[3]和3)羧基对金属中心的给能可以通过改变溶液的pH值来控制。因此，作为我们基于硫代金属配合物合理构建手性金属超分子结构的研究项目的一部分，我们新制备了具有两个依赖性COOH基团的手性CoIIIHgIICoIII三核配合物[Hg {CoACHTUNGTRENNUNG (l-Hcys)(en) 2} 2] ACHTUNGTRENNUNG (ClO4) 6 （1; lH 2cys= l-半胱氨酸）的三个非对构象（DLDL， LLLL和DLLL），并研究了COOH基团在水中去质子化诱导它们自组装的可能性。结果，我们发现1的LLLL异构体自组装成独特的（LLLL- coiiihgiicoiii） n金属螺旋结构(3)，而其DLDL异构体则转化为（DLDL- coiiihgiicoiii） 2二聚体结构(2)。此外，发现1的LLLL异构体在Cr3+存在下组装成（LLLL- coiiihgiicoiii） 6金属定位结构（4Cr），在其腔内包裹了一个水合铬achtungtrennung （III）离子。令我们惊讶的是，当在相同条件下处理1的中样dll异构体时，这种（LLLL-CoIIIHgIICoIII） 6金属定位化合物被完全分离出来。在这里，我们报告了这些显著的结果，以及在金属定位结构中加入另一种水金属离子（方案1）。化合物DLDL-1是由DL-[CoACHTUNGTRENNUNG (l-Hcys)(en) 2] ACHTUNGTRENNUNG (ClO4) 2[5]和HgACHTUNGTRENNUNG (ClO4) 2在HClO4水溶液中2:1反应分离得到的暗红色针状晶体。DLDL-1的红外光谱在1725 cm¿1，[6]处有一个比较尖锐的C= O拉伸带，表明存在COOH基团单晶x射线分析表明，DLDL-1是预期的s桥CoIIIHgIICoIII三核配合物，具有两个悬垂的COOH基团，DLDL-[Hg {CoACHTUNGTRENNUNG (l-Hcys)(en) 2} 2] ACHTUNGTRENNUNG (ClO4) 6（图1a）。在DLDL-1中，来自两个DL-[CoACHTUNGTRENNUNG (l-Hcys)(en) 2] 2+单位的两个硫代基团以大致线性几何的方式与中心HgII原子(Hg¿S= 2.381 (2) ä；S-Hg-S= 174.0(1) 8)，而采用赤道取向的COOH基团则…
During the past decade, metallosupramolecular architectures such as coordination rings, cages, and tubes have attracted considerable attention because of their structural characteristics and potential applications, which include the recognition and inclusion of small molecules and ions.[1, 2] In many cases, metallosupramolecules have been synthesized by means of metal-assisted assembly of organic molecules with several metal-binding sites,[1] which leads to the formation of thermodynamically stable assembled structures. On the other hand, examples of metallosupramolecular species created by the self-assembly of one kind of building block are relatively rare,[2] although this method is advantageous for the reversible control of assembled and disassembled structures by external factors. One way to achieve this is to design coordination compounds with vacant acceptor sites at a metal center, together with free donor groups that come to bind to another metal center in response to external factors. A mercury (II) coordination compound with free carboxyl groups is a potential candidate for creating a reversible self-assembly system because 1) a mercury (II) ion can adopt several coordination geometries, such as two-coordinated linear, three-coordinated T-shape, and four coordinated tetrahedron; 2) a mercury (II) ion has a good affinity not only for soft sulfur donors but also for hard oxygen donors;[3] and 3) the donating ability of carboxyl groups toward a metal center can be controlled by changing the pH of the solution. Thus, as part of our research project on the rational construction of chiral metallosupramolecular architectures based on thiolato metal complexes,[4] we newly prepared three diastereomers (DLDL, LLLL, and DLLL) of a chiral CoIIIHgIICoIII trinuclear complex with two pendent COOH groups,[Hg {CoACHTUNGTRENNUNG (l-Hcys)(en) 2} 2] ACHTUNGTRENNUNG (ClO4) 6 (1; lH 2cys= l-cysteine), and investigated the possibility of their self-assembly induced by the deprotonation of the COOH groups in water. As a result, we found that the LLLL isomer of 1 is self-assembled into a unique (LLLL-CoIIIHgIICoIII) n metallohelix structure (3), whereas its DLDL isomer was converted into a (DLDL-CoIIIHgIICoIII) 2 dimeric structure (2). In addition, the LLLL isomer of 1 was found to be assembled into a (LLLL-CoIIIHgIICoIII) 6 metallocage structure (4Cr) in the presence of Cr3+, encapsulating an aqua chromiumACHTUNGTRENNUNG (III) ion in its cavity. To our surprise, this (LLLL-CoIIIHgIICoIII) 6 metallocage compound was exclusively isolated when the mesolike DLLL isomer of 1 was treated under the same conditions. Herein we report on these remarkable results, together with the incorporation of another aqua metal ion in the metallocage structure (Scheme 1). Compound DLDL-1 was isolated as dark-red needle crystals from the 2: 1 reaction of DL-[CoACHTUNGTRENNUNG (l-Hcys)(en) 2] ACHTUNGTRENNUNG (ClO4) 2 [5] and HgACHTUNGTRENNUNG (ClO4) 2 in aqueous HClO4. The IR spectrum of DLDL-1 showed a relatively sharp C= O stretching band at 1725 cm¿ 1,[6] which suggests the presence of COOH groups.[7] Single-crystal X-ray analysis demonstrated that DLDL-1 is an expected S-bridged CoIIIHgIICoIII trinuclear complex with two pendent COOH groups, DLDL-[Hg {CoACHTUNGTRENNUNG (l-Hcys)(en) 2} 2] ACHTUNGTRENNUNG (ClO4) 6 (Figure 1a). In DLDL-1, the two thiolato groups from two DL-[CoACHTUNGTRENNUNG (l-Hcys)(en) 2] 2+ units coordinate to the central HgII atom in a roughly linear geometry (Hg¿ S= 2.381 (2) ä; S-Hg-S= 174.0 (1) 8), whereas the COOH groups that adopt an equatorial orientation do …