Department of Chemistry and Polymer Science, University of Stellenbosch , Matieland 7602, South Africa.
J Am Chem Soc. 2017 Apr 26;139(16):5923-5929. doi: 10.1021/jacs.7b01764. Epub 2017 Apr 14.
Two isoreticular three-dimensional copper(II) glutarate-based pillared-layered metal-organic frameworks (MOFs) with flexible pillars, [Cu(glu)(bpa)] and [Cu(glu)(bpp)] (bpa = 1,2-bis(4-pyridyl)ethane; bpp = 1,3-bis(4-pyridyl)propane), undergo spontaneous phase changes upon solvent loss at room temperature. Using single-crystal X-ray diffraction analysis (SCXRD), we show that the phase changes result in new narrow-channel forms that experience a large reduction in solvent-accessible volume. Moreover, the [Cu(glu)(bpa)] MOF displays a stepped sorption isotherm for the uptake of CO at room temperature. This is indicative of reversion of the framework to the wide-channel form under CO pressure. Supercritical CO was used to isolate the gas-included structures, and by means of SCXRD we were able to determine the positions of the CO molecules in the channels of the frameworks. Finally, we report the use of molecular modeling simulations to elucidate the phase-change mechanism, including the energetic changes involved. Structural limitations in both MOFs allow for only direct gauche-gauche enantiomeric interconversion of the glutarate moieties.
两个等结构的基于三维戊二酸铜（II）的柱状层状金属有机骨架（MOFs）具有柔性支柱，[Cu(glu)(bpa)]和[Cu(glu)(bpp)]（bpa=1,2-双（4-吡啶基）乙烷；bpp=1,3-双（4-吡啶基）丙烷），在室温下溶剂损失时会发生自发的相转变。使用单晶 X 射线衍射分析（SCXRD），我们表明相转变导致新的窄通道形式，经历了溶剂可及体积的大幅减少。此外，[Cu(glu)(bpa)] MOF 在室温下对 CO 的吸附表现出阶梯式吸附等温线。这表明在 CO 压力下框架会恢复到宽通道形式。超临界 CO 用于分离包含气体的结构，并且通过 SCXRD 我们能够确定框架通道中 CO 分子的位置。最后，我们报告了使用分子建模模拟来阐明相转变机制，包括涉及的能量变化。两个 MOFs 的结构限制仅允许戊二酸部分的直接 gauche-gauche 对映异构体相互转化。
