The focus in many fields of research is the generation of materials with adjustable
properties for specific applications. Among porous materials, metal-organic
frameworks (MOFs) have developed over the past 20 years to a material class with
enormous potential. Due to the modular design of MOFs from metal cations and
organic linkers, it is possible to tailor the properties of the resulting extended
frameworks by selecting individual components for the needs of specific applications.
Careful selection of metal ions and organic molecules with functional groups makes it
possible to adjust and influence the pore system, the type of linkage and the physical
and chemical properties of the framework.
In the present work, the main aspect was the preparation of a novel MOF with high
adjustability of its properties, based on light-induced postsynthetic reactions on the
organic linker molecules. The framework is composed of Zr4+ ion-based oxo clusters
and benzophenone-4,4'-dicarboxylate anions (bzpdc2–) as linker molecules. The
benzophenone unit is able to react with any molecule that contains C–H bonds after
excitation with photons, resulting in a covalent bond. This reaction opens the
possibility of changing the properties of the framework post-synthetically. The novel
Zr-bzpdc MOF is chemically and thermally stable and has a two-dimensional structure,
which opens up the possibility of obtaining nanometer-thin layers through
delamination methods. Further studies have shown that the adaptation of the surface
chemistry by the linkage of molecules has a huge impact on the dispersibility in polar
and nonpolar solvents. Furthermore, the direct polymerization of a conductive
polymer, starting from the surface of the MOF, yields electrically conductive
composite materials. Interestingly, in the course of this study it was found that the
unmodified MOF is also electrically conductive. Furthermore, a systematic study
concerned with the postsynthetic modification of Zr-bzpdc-MOF with alkanes and
alcohols of different chain lengths was undertaken. This showed that small hydrophilic
molecules react with all linker molecules throughout the crystal, whereas molecules
with longer chain lengths and thus more hydrophobic properties only modify the
surface of the MOF crystals.
The so far largely unaccessed approach to employ specific photochemical
modification reactions on the linker molecule the modification of MOFs has been
developed here to upgrade the novel Zr-bzpdc-MOF to an unexpectedly versatile
compound which is further augmented by the possibility to obtain nanosheets of this
substance. Various pathways to adapt this material to specific applications have thus
been opened up.
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