Metal Organic Framework
Metal-organic frameworks (English metal- organic frameworks, MOFs ) are microporous crystalline materials consisting of metallic junctions, the so-called SBUs (secondary building units) and organic molecules ( linkers ) are constructed as connecting elements between the nodes. It can be configured in one, two and three-dimensional networks, one - and two-dimensional structures are more likely to be regarded as coordination polymers, because they have no pores as the three-dimensional structures. The pores are filled by the synthesis with guest molecules (e.g., solvent or unreacted linkers ). By removal of the guest molecules but the pores can be made available, whereby collapse some networks. Potential applications can be found in gas storage (eg hydrogen, methane ), separation, sensing and catalysis.
For potential applications as catalysts is the large internal surface area (up to about 4500 m2 / g at the MOF -177 ) is of importance. The pore size can be set exactly on the size of the organic ligands, so that only the reactants of a certain size to fit into it. Thereby, a high selectivity can be expected.
In contrast to zeolites, ie inorganic crystals with pores of similar size, MOFs are less temperature-resistant. However, it is expected that the various possibilities of organic chemistry will lead to a greater variety of materials than in zeolites, and also the lower mass density is advantageous for some applications.
For materials that belong to the class of porous metal - organic frameworks, there is next to the abbreviation MOF still a wide variety of short names as IRMOF ( = IsoReticular Metal - Organic Framework), HKUST ( = Hong Kong University of Science & Technology), MIL ( = Matériaux de l' Institut Lavoisier ), ZIF ( = zeolitic imidazolates frameworks), COF ( = covalent Organic Frameworks ), BAF ( = Freiberg Framework), MFU ( = Metal - Organic Framework Ulm University), TOF ( = thorium Organic Framework), etc. for, inter alia, Rights are in charge of names and designations; So not everyone MOF must also be called " MOF ". Other designations as those mentioned above often refer to the origin or special properties of the compounds. Some well-known MOF structures are MOF -5, MOF -177, HKUST -1, MIL -53, BAF -4 and MFU -1. The best studied is MOF -5, whose formula is Zn4O (BDC ) 3. The unit cell consists of a Zn4O tetrahedron. To each edge of the tetrahedron is an organic ligand binds (1,4- Benzoldicarboxyl shortly BDC), the results of six molecules of each BDC Zn4O cluster. The other ends of the BDC molecules bind to other Zn4O cluster. This comes about a regular, cubic lattice, in which the Zn4O cluster the vertices of the cube and the BDC molecules form the edges. In the voids within the cubes remain molecules of the solvent which is used for synthesis, back. The solvent is removed by heating.
Analog 2D structures may be observed on surfaces directly by scanning tunneling microscopy.
A novel process for preparing metal- organic frameworks ( MOFs), researchers from the Institute of Functional Interfaces (IFG ) of KIT, which develops Jacobs University Bremen and other facilities. Here, the MOF structures grown epitaxially, ie layer by layer, on the surface of substrates ( SURMOFs - Surface Mounted Metal Organic Frameworks ). Thus, the size and shape of the pores can be as well as their chemical functionality for each application to tailor. A special method, known as liquid phase epitaxy ( LPE - Liquid Phase Epitaxy ) allows also to produce scaffold structures that can not be generated using normal wet chemical methods. For the production of this novel, known as SURMOFs 2 series of MOFs, the researchers synthesized several organic molecules of different lengths. The pore size of the new metal- organic frameworks is up to three times three nanometers. The researchers are working on the length of the organic striving to further enlarge to embed even larger proteins and in the next step even metallic nanoparticles in the framework structures, which would allow for interesting applications in optics and photonics.