Synthesis and hydrogen adsorption properties of internally polarized 2,6-azulenedicarboxylate based metal–organic frameworks
作者:Samir Barman、Anupam Khutia、Ralph Koitz、Olivier Blacque、Hiroyasu Furukawa、Marcella Iannuzzi、Omar M. Yaghi、Christoph Janiak、Jürg Hutter、Heinz Berke
DOI:10.1039/c4ta04393f
日期:——
To improve the binding energy of hydrogen, incorporation of internally polarized organic units into metalâorganic frameworks (MOFs) should be a promising strategy. In this study, two novel MOFs composed of internally polarized 2,6-azulenedicarboxylate (2,6-azd), termed MOF-649 [Zn2(2,6-azd)2(dabco), where dabco = 1,4-diazabicyclo[2.2.2]octane] and MOF-650 [Zn4O(2,6-azd)3], have been synthesized, and their crystal structures were determined by single-crystal X-ray diffraction analyses. Both materials displayed permanent microporosity, and the BrunauerâEmmettâTeller (BET) surface areas of MOF-649 and MOF-650 are estimated to be 910 and 2630 m2 gâ1, respectively. The H2 adsorption measurements showed that MOF-650 adsorbs 14.8 mg gâ1 of hydrogen at 77 K and 1 bar. The polarization effect of the azulene unit in the framework is supported by high initial isosteric heat of adsorption of 6.8 kJ molâ1 for MOF-650. A detailed computational analysis using density functional theory was carried out in order to investigate the structure and electronic properties of MOF-650 and subsequently to understand its site-specific interactions with hydrogen.
为了提高氢的结合能,将内部极化的有机单元合并到金属有机框架(MOF)中应该是一种有前景的策略。在本研究中,两种新型 MOF 由内部极化的 2,6-azulenedicarboxylate (2,6-azd) 组成,称为 MOF-649 [Zn2(2,6-azd)2(dabco),其中 dabco = 1,4-二氮杂双环合成了[2.2.2]辛烷]和MOF-650 [Zn4O(2,6-azd)3],并通过单晶X射线衍射分析确定了它们的晶体结构。两种材料均表现出永久微孔性,MOF-649 和 MOF-650 的 Brunauer–Emmett–Teller (BET) 表面积估计分别为 910 和 2630 m2 g–1。 H2 吸附测量表明,MOF-650 在 77 K 和 1 bar 下吸附了 14.8 mg g·1 的氢气。 MOF-650 6.8 kJ mol·1 的高初始等量吸附热支持了框架中甘菊环单元的极化效应。使用密度泛函理论进行了详细的计算分析,以研究 MOF-650 的结构和电子特性,并随后了解其与氢的位点特异性相互作用。