Dye Encapsulation Inside a New Mesoporous Metal-Organic Framework for Multifunctional Solvatochromic-Response Function
Dye Encapsulation Inside a New Mesoporous Metal-Organic Framework for Multifunctional Solvatochromic-Response Function
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DOI：
10.1002/chem.201202352
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发表时间：
2012-10-01
影响因子：
4.3
通讯作者：
Kaskel, Stefan
中科院分区：
文献类型：
--
作者：
Gruenker, Ronny;Bon, Volodymyr;Kaskel, Stefan
Metal–organic frameworks (MOFs), hybrid materials built up from metal clusters and organic linkers, have shown a huge potential for a wide range of applications.[1] In recent years, MOFs have set new records in terms of specific surface areas and pore volumes [2, 3] and therefore are highly suitable as storage materials for small and large molecules. The development of new materials is crucial for the improvement of storage devices, but MOFs are also ideal candidates for functionalization. One functionalization strategy is the integration of complex organic linker molecules containing secondary functional groups.[4] However, this approach is synthetically demanding and not general, because functional donor atoms may affect the linker connectivity resulting in unexpected network topologies. A second powerful strategy is postsynthetic modification of the framework.[5] In this case, the range of functions is restricted due to the limited stability of MOFs against aggressive chemicals. A modular and more versatile approach may be the encapsulation of functional guest molecules into the MOF material. However, for these systems leaching is critical. A crucial requirement in all cases is also the accessibility of MOF functionalities for guest molecules. In this context, a large pore size is highly beneficial. However, the development of such mesoporous frameworks is challenging, because expanded frameworks are often more fragile leading to a collapse of the framework during removal of included guests molecules. A very effective concept to achieve robust frameworks lies in the creation of hierarchical pore structures by combination of two different linker molecules.[6] The most prominent examples of such copolymerization approach are UMCM-1/À2/À3,[7, 8, 9] DUT-6 [10] and DUT-23 [11] or MOF-210.[3] In the case of DUT-23, auxiliary linker was used successfully to avoid interpenetration and to enhance the robustness, which resulted in highly porous structures. To date, this concept was restricted only to the combination of triand ditopic linkers. On the other hand, DUT-10 (M)(M= Zn, Cu, Co) compounds based on the tetratopic N, N, N’, N’-benzidinetetrabenzoate (benztb) ligand and the paddlewheel secondary building unit (SBU) undergo structural change upon solvent removal.[12] By enhancing the connectivity of the framework by using a six-connecting [Zn4O] 6+ cluster instead of a four-connecting paddle–wheel, DUT-13, a framework stable upon solvent removal was obtained.[13] Nevertheless, a structural change was observed during the physisorption of nonsupercritical gases (eg, nitrogen at 77 K).The aim of this work was to stabilize benztb-based mesoporous MOFs by cross-linking with auxiliary benzene-1, 3, 5-tribenzoate (btb) ligand and to design new robust frameworks suitable for functionalization with accessible complex functions. Herein, the first remarkable MOF system in this series,[Zn4OACHTUNGTRENNUNG (benztb) ACHTUNGTRENNUNG (btb) 2/3](DUT-25, DUT= Dresden University of Technology), is presented. The new material is highly robust upon solvent removal and has an extremely high porosity demonstrated by gas and liquid-phase adsorption experiments. Furthermore, the system is ideally suited for effective functionalization with accessible and fully functional guest molecules without causing degradation of the network structure.
Metal–organic frameworks (MOFs), hybrid materials built up from metal clusters and organic linkers, have shown a huge potential for a wide range of applications.[1] In recent years, MOFs have set new records in terms of specific surface areas and pore volumes [2, 3] and therefore are highly suitable as storage materials for small and large molecules. The development of new materials is crucial for the improvement of storage devices, but MOFs are also ideal candidates for functionalization. One functionalization strategy is the integration of complex organic linker molecules containing secondary functional groups.[4] However, this approach is synthetically demanding and not general, because functional donor atoms may affect the linker connectivity resulting in unexpected network topologies. A second powerful strategy is postsynthetic modification of the framework.[5] In this case, the range of functions is restricted due to the limited stability of MOFs against aggressive chemicals. A modular and more versatile approach may be the encapsulation of functional guest molecules into the MOF material. However, for these systems leaching is critical. A crucial requirement in all cases is also the accessibility of MOF functionalities for guest molecules. In this context, a large pore size is highly beneficial. However, the development of such mesoporous frameworks is challenging, because expanded frameworks are often more fragile leading to a collapse of the framework during removal of included guests molecules. A very effective concept to achieve robust frameworks lies in the creation of hierarchical pore structures by combination of two different linker molecules.[6] The most prominent examples of such copolymerization approach are UMCM-1/À2/À3,[7, 8, 9] DUT-6 [10] and DUT-23 [11] or MOF-210.[3] In the case of DUT-23, auxiliary linker was used successfully to avoid interpenetration and to enhance the robustness, which resulted in highly porous structures. To date, this concept was restricted only to the combination of triand ditopic linkers. On the other hand, DUT-10 (M)(M= Zn, Cu, Co) compounds based on the tetratopic N, N, N’, N’-benzidinetetrabenzoate (benztb) ligand and the paddlewheel secondary building unit (SBU) undergo structural change upon solvent removal.[12] By enhancing the connectivity of the framework by using a six-connecting [Zn4O] 6+ cluster instead of a four-connecting paddle–wheel, DUT-13, a framework stable upon solvent removal was obtained.[13] Nevertheless, a structural change was observed during the physisorption of nonsupercritical gases (eg, nitrogen at 77 K).The aim of this work was to stabilize benztb-based mesoporous MOFs by cross-linking with auxiliary benzene-1, 3, 5-tribenzoate (btb) ligand and to design new robust frameworks suitable for functionalization with accessible complex functions. Herein, the first remarkable MOF system in this series,[Zn4OACHTUNGTRENNUNG (benztb) ACHTUNGTRENNUNG (btb) 2/3](DUT-25, DUT= Dresden University of Technology), is presented. The new material is highly robust upon solvent removal and has an extremely high porosity demonstrated by gas and liquid-phase adsorption experiments. Furthermore, the system is ideally suited for effective functionalization with accessible and fully functional guest molecules without causing degradation of the network structure.