Esrafili Leili, Cheung Ocean, Adriaensens Peter, Derveaux Elien, Glasby Lawson T, Moghadam Peyman Z, Vande Velde Christophe M L
iPRACS, Faculty of Applied Engineering, University of Antwerp Groenenborgerlaan 171 2020 Antwerpen Belgium
Nanotechnology and Functional Materials, Department of Materials Science and Engineering, Uppsala University SE75121 Sweden.
RSC Adv. 2025 Aug 1;15(34):27531-27543. doi: 10.1039/d5ra02649k.
In the synthesis of metal-organic frameworks (MOFs), efforts to increase the pore sizes by elongating linkers often result in interpenetration, a challenge that is exacerbated when functional groups are added. Urea groups and their derivatives play an important role in supramolecular chemistry by providing directional hydrogen bonding donor sites and are often considered "privileged groups". Incorporating these moieties into MOFs allows for their spatial separation, a critical approach to enhancing their functional activity, simultaneously preventing interpenetration, and enlarging the pore size. In this study, we synthesized hydrophilic urea-functionalized MOFs using zinc ions and the ligands 4,4'-(carbonylbis(azanediyl))dibenzoic acid (L1) and 1,3-di(pyridin-4-yl)urea (L2). Different levels of interpenetration and pore size were produced by varying temperature and starting material concentrations. UA-1 and UA-2 displayed 4-fold interpenetration. Notably, UA-3 formed non-interpenetrated 1D hexagonal mesoporous channels with six urea groups around each hexagonal pore, making it the first example of a non-interpenetrated mesoporous urea MOF. This topology differs from existing RCSR representations. We also investigated the host-guest interactions when introducing various organic molecules into UA-3, using a combination of single crystal X-ray diffraction (SCXRD), thermogravimetric analysis (TGA) and solid-state nuclear magnetic resonance (ss-NMR) spectroscopy. SCXRD provided insight into the amount and position of solvent molecules within the channels of the framework.
在金属有机框架（MOF）的合成中，通过延长连接体来增加孔径的努力常常导致互穿现象，当添加官能团时，这一挑战会更加严峻。脲基及其衍生物通过提供定向氢键供体位点在超分子化学中发挥重要作用，并且常常被视为“特权基团”。将这些部分纳入MOF中可以实现它们的空间分离，这是增强其功能活性、同时防止互穿以及扩大孔径的关键方法。在本研究中，我们使用锌离子以及配体4,4'-（羰基双（氮杂二亚基））二苯甲酸（L1）和1,3-二（吡啶-4-基）脲（L2）合成了亲水性脲官能化的MOF。通过改变温度和起始原料浓度产生了不同程度的互穿和孔径。UA-1和UA-2表现出4重互穿。值得注意的是，UA-3形成了非互穿的一维六方介孔通道，每个六边形孔周围有六个脲基，这使其成为非互穿介孔脲MOF的首个实例。这种拓扑结构不同于现有的RCSR表示。我们还使用单晶X射线衍射（SCXRD）、热重分析（TGA）和固态核磁共振（ss-NMR）光谱相结合的方法，研究了将各种有机分子引入UA-3时的主客体相互作用。SCXRD提供了关于框架通道内溶剂分子数量和位置的见解。
