Metal Organic Frameworks (MOFs) are large three-dimensional (3D) molecules containing a highly symmetrical channel structure, whose surface area can reach the size of a football field and beyond. These molecules are built from an intricate arrangement of polyhedra, which in turn are built from metal centers connecting organic linkers. The organic linkers are concatenated, sometimes via additional linkers, to turn the compound into a crystalline lattice. Their large surface area and the possibility to host a plethora of molecules makes MOFs synthetically and industrially extremely relevant. Applications of MOFs range from hydrogen storage, over possible vaccine carriers to such trivial things like drying agents. Research on MOFs has shown that the organic linkers can be modified or exchanged relatively easily allowing to precisely tailor the MOF structure to the desired application.
Covalent Organic Frameworks (COFs) are similar to MOFs but are completely built from organic building units (mainly H, C, B, N and O) and held together by strong covalent bonds. Even though they contain mainly light scatterers X-ray diffraction is an excellent method to investigate their structures.
Checking the outcome of a new MOF/COF synthesis is most conveniently done by single crystal X-ray diffraction, offering a quick way to understand the atomic arrangements and the geometry of the cavities. The location of the adsorbed guest molecules can also be precisely analyzed via single crystal diffraction.
Also powder diffraction has proven to be a valuable technique for research on MOFs and COFs. It is an excellent method to investigate the structural arrangement of newly designed MOFs/COFs and the experimental outcome of work with already known compounds. Moreover, powder diffraction can be conducted at variable temperatures to observe desorption of the guest molecule in-situ or test the MOFs/COFs temperature stability.
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