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TRANSCRIPT
Cross-Linking of Metal Organic Frameworks
Kazuki Sada
Department of Chemistry, Faculty of Science, Hokkaido University, Japan*E-mail: [email protected], Tel: +81-(0)11-706-3473
Metal organic frameworks (MOFs) have been attracting continuous interest as nano-porous crystalline
materials due to their structural robustness and inclusion of guest molecules for catalysis, storage, and
separation. In this presentation, we demonstrate cross-linking of the organic ligands in MOF crystals to
transform to polymer networks without decomposition of crystalline state by the following two systems;
cyclodextrin MOF (CD-MOF) cross-linked by diglycidyl ethers and (2) azide-tagged MOF (AzM) cross-
linked by multi-alkyne cross-linkers via click reaction.
In the first system, cubic crystals of CD-MOF in the range of several hundred nm to mm were prepared
by reacting -CD with aqueous KOH, followed by vapor diffusion of methanol. The cross-linking reaction
was carried out by treatment with ethylene glycol diglycidyl ether (L) to cross-link between OHs of each -
CD unit in the CD-MOF pores. After degradation of the coordination bonds by repeated soaking in
EtOH/H2O, they became insoluble and swelled in H2O. This indicated that they were converted to polymer
gels by the cross-linking of the organic linkers in the MOF crystals. In the second system, azide-tagged MOF
(AzM) crystals were subjected to click reaction with tetra-acetylene cross-linker (CL4) to cross-link the
organic ligands. After decomposition of the coordination bonds, the MOF crystals gradually swelled and
became insoluble polymer gels. In both cases, the sizes and the shapes of the resulting polymer gels were
very similar to those of the starting MOF crystals, and the chracteristic polyhedral shapes with well-defined
faces originated from the templated MOF crystals were preserved during transformation processes.
In conclusion, the cross-linking of MOF opens a new horizon for the preparation of micro- and nano-sized
polyhedral polymer gels. Our system is the first example for connecting polymer gels as soft and wet
amorphous materials with MOF crystals as robust and crystalline materials with respect to three-dimensional network structures.