Hierarchical Self-Assembly of a Chiral Metal-Organic Framework Displaying Pronounced Porosity
Hierarchical Self-Assembly of a Chiral Metal-Organic Framework Displaying Pronounced Porosity
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DOI：
10.1002/anie.200905497
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发表时间：
2010-01-01
影响因子：
16.6
通讯作者：
Lindoy, Leonard F.
中科院分区：
文献类型：
--
作者：
Clegg, Jack K.;Iremonger, Simon S.;Lindoy, Leonard F.
近年来，人们对发展有用的自组装杂化材料给予了极大的关注。[1]金属有机骨架(MOF)的情况尤其如此，它具有规律性、孔隙率、稳健性和高比表面积等性质，在催化、气体分离和存储等领域具有潜在的应用。[2，3]我们的研究小组和其他人一直在开发合成离散和扩展金属-有机材料的新方法，特别是对结构复杂性增加的受控生成感兴趣。[4]在此，我们报告了一种分级自组装策略，该策略已被用于合成新的金属-有机骨架。这种方法不同于通常使用的分子构造块(MBB)和二次构筑单元(SBU)方法，在这两种方法中，单个金属离子或小的无机簇(多面体)通过一锅反应中的桥联(通常是羧酸盐)配体连接在一起。在这些方法中，大量的孔体积主要是通过在热力学上有利的开放骨架的形成来实现的，克服了与溶剂客体分子捕获相关的熵损失。对骨架形成的动力学控制主要是通过反复优化合成条件来实现的，以防止不需要的动力学中间体的形成。[6]在这里使用的分层方法中，我们采用了一系列不同的自组装步骤，这些步骤跨越不同的复杂性水平，将预先设计的、动力学稳定的、离散的中性超分子组件整合到金属-有机骨架中。通过这种方式，我们证明了将分立子组件的属性转录成框架产品的属性是可能的。该方法包括初始设计和组装包含不饱和金属中心的离散二维(2D)孔洞Tecon，然后将这些位置与桥联基团连接，从而有可能将子组分中的2D空位转换为骨架材料中的3D空位。通过使用这种方法，我们已经产生了一种新的中性手性MOF，它表现出显著的孔隙率和气体吸附行为，从而证明我们的离散构建块的主客体属性可以成功地赋予最终的MOF。在我们组装含有β-二酮配体的金属体系的成熟方法的基础上，[7，8]我们构建了大的离散三角子组分[Cu3L3]。这一部分在这类离散体系中相对不常见，因为它包含配位的不饱和金属中心和大的空隙面积-这两个属性都是形成具有显著孔隙率的MOF的有用属性。在Na2CO3存在下，目标络合物[Cu3L3]·H2O以80%的产率与配体在四氢呋喃中的溶液缓慢加成。微观分析证实了上述化学计量比，并与我们和其他人所描述的相关较小的三核铜配合物类似地被指定为三角形结构。[8，9]密切相关的CoII配合物[10][Co3L3(Py)6]·5.55py·0.6H2O(py=吡啶)的单晶X射线衍射分析结果支持了这一归属。该产品在…中具有预期的离散三角结构(图1；另请参阅支持信息中的图S5)
Significant recent attention has been devoted to the development of useful self-assembled hybrid materials.[1] This is particularly the case for metal–organic frameworks (MOFs), which display properties such as regularity, porosity, robustness, and high surface area that lead to potential applications in areas such as catalysis, gas separation, and storage.[2, 3] Our research groups and others have been developing new methods for the synthesis of both discrete and extended metal–organic materials, with particular interest in the controlled generation of increased structural complexity.[4] Herein we report a hierarchical self-assembly strategy which has been used to synthesize a new metal–organic framework. This strategy differs from the commonly employed molecular building block (MBB) and secondary building unit (SBU) approaches, where single metal ions or small inorganic clusters (polyhedra) are linked by bridging (often carboxylate) ligands in a one-pot reaction.[5] In these approaches, substantial pore volume is achieved principally through the enthalpically favorable formation of an open framework overcoming the entropic penalties associated with the entrapment of solvent guest molecules. Kinetic control over the formation of the framework is achieved largely through the trial-and-error optimization of synthetic conditions to prevent formation of unwanted kinetic intermediates.[6] In the hierarchical approach used here we have employed a series of distinct self-assembly steps, which operate across different levels of complexity, to incorporate predesigned, kinetically stable, discrete neutral supramolecular components into a metal–organic framework. In this way we show that it is possible to transcribe the properties of the discrete subcomponent into those of the framework product. This method involves the initial design and assembly of a discrete two-dimensional (2D) void-containing tecton containing unsaturated metal centers, followed by linkage of these sites with a bridging group in such a way that it is possible to transform the 2D voids in the subcomponent into 3D voids in a framework material. By using this approach we have generated a new neutral chiral MOF that displays significant porosity and gas-sorption behavior, and hence demonstrate that the host–guest properties of our discrete building blocks can be successfully imparted to the final MOF. Building on our well-established methods for assembling metallosystems incorporating β-diketone ligands,[7, 8] we constructed the large discrete triangular subcomponent [Cu3L3]. This moiety is relatively unusual among discrete systems of this type in that it contains coordinatively unsaturated metal centers in combination with a large void area—both useful attributes for the formation of a MOF with significant porosity.H2L (Scheme 1) was synthesized by a Claisen condensation between dimethyl biphenyl-4, 4’-dicarboxylate and 3, 3-dimethylbutan-2-one (the synthesis and characterization of H2L is given in the Supporting Information). The target complex [Cu3L3]· H2O was formed in 80% yield after slow addition of copper (II) chloride to a solution of the ligand in THF in the presence of Na2CO3. Microanalysis confirmed the above stoichiometry, and the product was assigned a triangular structure by analogy with related smaller trinuclear copper complexes previously described by us and others.[8, 9] This assignment was supported by the results of a single-crystal X-ray diffraction analysis of the closely related CoII complex [10][Co3L3 (py) 6]· 5.55 py· 0.6 H2O (py= pyridine). This product has the expected discrete triangular structure (Figure 1; see also Figure S5 in the Supporting Information) in …