Kinetic gate-opening process in a flexible porous coordination polymer.-猫眼课题宝

DOI：

10.1002/anie.200705822

发表时间：

2008-05

期刊：

Angewandte Chemie

影响因子：

通讯作者：

中科院分区：

文献类型：

作者：

D. Tanaka;Keiji Nakagawa;Masakazu Higuchi;S. Horike;Y. Kubota;Tatsuo C. Kobayashi;M. Takata;S. Kit

近年来，人们对柔性和动态多孔配位聚合物（pcp）的性质越来越感兴趣，这些聚合物可以根据客体吸附可逆地改变其结构和性质在一位现任作者预测了它们的重要性之后，仅在十年内就制备了100多种柔性pcp。所谓的结构动力学已被确定为高选择性、[3]调节、[4]和分子传感的关键原理在柔性pcp中最有趣的现象之一是由客体诱导的框架转变引起的逐步吸附。[3,4,6]特别是在特定压力下，吸附过程中，当骨架结构从封闭结构转变为开放结构时，会产生门效应，从而产生s型或s型吸附曲线。封闭结构沟槽的闸门开启时的起始压力称为闸门开启压力（Pgo），它与主体框架的结构转变有关有趣的是，Pgo的值显示了客户机依赖这种吸附物之间的差异表明，柔性pcp在许多领域都有潜在的应用，包括分离、传感器和开关材料。特别是，小气体吸附剂，如O2， Ar和N2，是有吸引力的研究目标，首先是因为这些类似气体分子之间的吸附行为的差异引起了广泛的商业兴趣，如空气分离过程，也因为它们简单的结构和物理性质的微小差异的科学兴趣然而，仍有几个问题没有得到解答。为什么Pgo以下不发生吸附？什么决定Pgo？如何增强不同来宾的Pgo差异？一般来说，具有小迟滞的s型等温线被认为是协同现象的结果一些柔性pcp在高相对压力下实际上表现出等温线不连续，具有较大的滞后，其中动力学将发挥重要作用。[11,12]尽管它们很重要，但很少有人尝试确定门效应的动力学。[11,13]本文研究了柔性PCP {[Cd (bpndc)(bpy)]} n （1; bpndc=二苯甲酮- 4,4′-二羧酸酯，bpy= 4,4′-联吡啶基）的合成、晶体结构和气体吸附性能，结果表明O2、Ar和N2对Pgo的吸附有很大差异（图1）。为了理解类似气体之间差异背后的机制，我们借助一种新的扩散模型来处理这种现象，在这种模型中，吸附是通过中间物的形成进行的。动力学分析表明，中间体的形成可以被描述为一个闸门打开过程，控制Pgo并增强气体之间的差异。Cd (NO3) 2·4 H2O、H2bpndc和bpy在二甲基甲酰胺（DMF）中的溶剂热反应生成了溶剂化框架化合物{[Cd (bpndc)(bpy)](DMF) (H2O)} n （1' solvent）。单晶x射线分析表明，镉离子通过bpndc沿c轴连接形成{[Cd (bpndc)]} n的一维双链结构，并通过bpy沿b轴连接形成二维片基序（图2a和b）。2D层相互交错，形成一个3D组装框架（图2c）。这与先前报道的pcp相似，显示出灵活的性质溶剂的三维结构由a

Recently, there has been growing interest in the nature of flexible and dynamic porous coordination polymers (PCPs) that reversibly change their structures and properties in response to guest adsorption.[1] After one of the present authors predicted their importance,[2] many flexible PCPs have been prepared in only a decade. So-called structural dynamism has been identified as a key principle for high selectivity,[3] accommodation,[4] and molecular sensing.[5] One of the most interesting phenomena in flexible PCPs is stepwise adsorption caused by the guest-induced framework transition.[3, 4, 6] In particular, a gate effect occurs when the framework structure changes during the adsorption process from a closed structure to an open one at a specific pressure, which generates an S-shaped or sigmoidal adsorption profile. The onset pressure at which the gates of the closed-structure grooves become open is referred to as the gate-opening pressure (Pgo) and is related to the structural transformation of the host framework.[7] Interestingly, the value of Pgo shows a guest dependency.[8] This difference between adsorbates suggests that flexible PCPs have potential applications in many fields, including separation, sensors, and switching materials. In particular, small gaseous adsorbates, such as O2, Ar, and N2, are attractive targets for research, first because the differences in sorption behavior between such similar gas molecules have attracted wide commercial interest for processes such as air separation, and also because of scientific interest as a result of their simple structures and small differences in physical properties.[9] However, several questions remain unanswered. Why does adsorption not occur below Pgo? What determines Pgo? How can the difference in Pgo for different guests be enhanced? Generally, a sigmoid isotherm with small hysteresis has been understood to be the result of cooperative phenomena.[10] Several flexible PCPs actually show isotherm discontinuities at high relative pressure, with large hysteresis, where kinetics would play an essential role.[11, 12] In spite of their importance, few attempts have been made to determine the kinetics of the gate effect.[11, 13] Herein, we present the synthesis, crystal structure, and gas sorption properties of a flexible PCP,{[Cd (bpndc)(bpy)]} n (1; bpndc= benzophenone-4, 4’-dicarboxylate, bpy= 4, 4’-bipyridyl), which shows a large difference in Pgo between O2, Ar, and N2 (Figure 1). To understand the mechanism behind the differences between similar gases, we treat this phenomenon with the aid of a new diffusion model in which adsorption proceeds through the formation of an intermediate. Kinetic analysis revealed that the formation of the intermediate, which can be described as a gate-opening process, governs Pgo and enhances the difference between gases.The solvothermal reaction of Cd (NO3) 2· 4 H2O, H2bpndc, and bpy in dimethylformamide (DMF) produced the solvated framework compounds {[Cd (bpndc)(bpy)](dmf)(H2O)} n (1'Solvents). Single-crystal X-ray analysis demonstrated that cadmium ions are connected by bpndc to produce 1D double-chain structures of {[Cd (bpndc)]} n along the c axis, and are linked by bpy along the b axis to give a 2D sheet motif (Figure 2a and b). The 2D layers are mutually interdigitated to create a 3D assembled framework (Figure2c). This is similar to previously reported PCPs that show a flexible nature.[14] The 3D structure of 1'Solvents consists of a

Kinetic gate-opening process in a flexible porous coordination polymer.

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