ERATO Kitagawa Integrated Pores Project, Japan Science and Technology Agency (JST), Kyoto Research Park Bldg #3-405, Kyoto 600-8815, Japan.
J Am Chem Soc. 2011 Jun 15;133(23):9005-13. doi: 10.1021/ja201484s. Epub 2011 May 20.
A new synthetic approach to prepare flexible porous coordination polymers (PCPs) by the use of soft secondary building units (SBUs) which can undergo multiple reversible metal-ligand bonds breaking is reported. We have prepared a zinc paddle-wheel-based two-fold interpenetrated PCP, {[Zn(2)(tp)(2)(L(2))]·2.5DMF·0.5water}(n) (2a, H(2)tp = terephthanlic acid; L(2) = 2,3-difluoro-1,4-bis(4-pyridyl)benzene), showing dynamic structural transformations upon the removal and rebinding of guest molecules. The X-ray structures at different degrees of desolvation indicate the highly flexible nature of the framework. The framework deformations involve slippage of the layers and movement of the two interpenetrated frameworks with respect to each other. Interestingly, the coordination geometry of a zinc paddle-wheel unit (one of the popular SBUs) is considerably changed by bond breaking between zinc and oxygen atoms during the drying process. Two zinc atoms in the dried form 2d reside in a distorted tetrahedral geometry. Compound 2d has no void volume and favors the uptake of O(2) over Ar and N(2) at 77 K. The O(2) and Ar adsorption isotherms of 2d show gate-opening-type adsorption behaviors corroborating the structure determination. The CO(2) adsorption isotherm at 195 K exhibits multiple steps originating from the flexibility of the framework. The structural transformations of the zinc clusters in the framework upon sorption of guest molecules are also characterized by Raman spectroscopy in which the characteristic bands corresponding to ν(sym)(COO(-)) vibration were used.
一种新的合成方法，通过使用可以经历多个可逆金属-配体键断裂的软次级建筑单元（SBUs）来制备柔性多孔配位聚合物（PCPs）。我们已经制备了一种基于锌桨轮的两倍互穿 PCP，{[Zn(2)(tp)(2)(L(2))]·2.5DMF·0.5water}(n)（2a，H(2)tp = 对苯二甲酸；L(2) = 2,3-二氟-1,4-双（4-吡啶基）苯），在去除和重新结合客体分子时表现出动态结构转变。不同程度去溶剂化的 X 射线结构表明了框架的高度灵活性。框架变形涉及层的滑动和两个互穿框架之间的相对移动。有趣的是，在干燥过程中锌和氧原子之间的键断裂导致锌桨轮单元（流行的 SBU 之一）的配位几何形状发生了相当大的变化。干燥形式 2d 中的两个锌原子位于扭曲的四面体形几何形状中。化合物 2d 没有空隙体积，并且在 77 K 下有利于 O(2)而不是 Ar 和 N(2)的吸收。2d 的 O(2)和 Ar 吸附等温线显示出与结构确定相符的开门型吸附行为。195 K 时的 CO(2)吸附等温线表现出多个步骤，这源于框架的灵活性。在框架中吸附客体分子时，锌簇的结构转变也通过拉曼光谱进行了表征，其中使用了对应于 ν(sym)(COO(-))振动的特征带。
