528
K. Sada and K. Kokado
dissolved in N,N-diethylformamide (DEF) with zinc nitrate hexahydrate, followed
by heating at 80°C to yield a pale yellow cubic-shaped crystal of N3-MOF16 (Scheme 25.2a). Since it showed a similar powder X-ray diffraction pattern as
IRMOF-16 consisting of zinc (II) ion and terphenyl dicarboxylic acid, it has the same
infinite periodic lattice structure with the formation of the cluster of Zn 4 -O-(OOCR) 6
from the six organic ligands as the connectivity of IRMOF-16. To this MOF, various
terminal alkynes, such as methyl propiolate, propargyl alcohol, 1-hexyne, and propargylamine, caused the CuAAC reaction in the presence of copper bromide in DEF.
The characteristic FT-IR band around 2100 cm
−1 for the azide group completely
disappeared in 30 min and
1 H NMR measurement after the acid hydrolysis represented the new peaks from the triazole ring. Also notably, since the X-ray diffraction
pattern before and after the reaction did not change, the crystallinity of the MOF was
found to be preserved during the click reaction. Therefore, this system should be one
of the examples of the PSM for the MOF.
In the same year, Nguyen and coworkers reported surface modifications of a
trimethylsilyl (TMS)-protected alkyne-tagged MOF by the same reaction after the
deprotection of the TMS group by tetrabutylammonium fluoride (TBAF) [27, 28]
(Scheme 25.2b). In this reaction, the alkyne-tagged MOF was reacted with azides
introduced from the external solution. A strong fluorescence was observed only on
the surface of the MOF after the treatment of the azide with ethidium bromide as a
fluorophore. As another example, the surface hydrophilicity and wettability of the
MOF could be changed by employing CuAAC with the azide-terminated polyethylene glycol (PEG). Subsequently, the same authors synthesized the core-shell MOF
modified with two different azides by controlling the deprotecting reagents of the
TMS-protected alkyne-tagged MOF [28]. In the multiple deprotection and CuAAC,
the crystallinity and the nanoporous structure of the MOF were well maintained.
Since the organic ligand having an azide group is not commercially available for
the PSM of the MOF, it is necessary to synthesize them through the several steps of
organic reactions. This should be a drawback for the CuAAC for the PSM. In 2010,
Farrusseng and colleagues reported a one-pot, two-step PSM from aminoterephthalic
acid as the common starting material by the direct conversion of the amino group
to the azide group [29] (Scheme 25.2c). They first prepared a series of MOF, called
DMOF-NH 2 and MIL-68(In)-NH 2 . The PSM of the amino group to the azide group in
the MOF was then done by the treatment of nitrite tert-butyl and trimethylsilylazide
in a THF solution at room temperature, followed by the CuAAC with the terminal
alkynes in the presence of copper (I) hexafluorophosphate. The resulting MOF was
achieved by quantitative modification of the organic ligand. The surface area of
the pores by this modification was reduced to 9–18% of the original MOF, and the
pore volume by 6–14%. This method is applicable to other MOF such as IRMOF3, MIL-101-NH 2 , CAU-1, and MIL-53 providing many functional modified MOF.
They also demonstrated that a large number of alkynes, such as phenylacetylene,
propargylamine, 1-hexyne, propargyl alcohol, and propiolic acid, can be used to
react with the MOF. Since the first step has a low efficiency due to the low diffusion
rate in the nanopores, a high excess amount of trimethylsilylazide should be required
for the quantitative conversion. Some limitation to the type of functional groups of the
K. Sada and K. Kokado
dissolved in N,N-diethylformamide (DEF) with zinc nitrate hexahydrate, followed
by heating at 80°C to yield a pale yellow cubic-shaped crystal of N3-MOF16 (Scheme 25.2a). Since it showed a similar powder X-ray diffraction pattern as
IRMOF-16 consisting of zinc (II) ion and terphenyl dicarboxylic acid, it has the same
infinite periodic lattice structure with the formation of the cluster of Zn 4 -O-(OOCR) 6
from the six organic ligands as the connectivity of IRMOF-16. To this MOF, various
terminal alkynes, such as methyl propiolate, propargyl alcohol, 1-hexyne, and propargylamine, caused the CuAAC reaction in the presence of copper bromide in DEF.
The characteristic FT-IR band around 2100 cm
−1 for the azide group completely
disappeared in 30 min and
1 H NMR measurement after the acid hydrolysis represented the new peaks from the triazole ring. Also notably, since the X-ray diffraction
pattern before and after the reaction did not change, the crystallinity of the MOF was
found to be preserved during the click reaction. Therefore, this system should be one
of the examples of the PSM for the MOF.
In the same year, Nguyen and coworkers reported surface modifications of a
trimethylsilyl (TMS)-protected alkyne-tagged MOF by the same reaction after the
deprotection of the TMS group by tetrabutylammonium fluoride (TBAF) [27, 28]
(Scheme 25.2b). In this reaction, the alkyne-tagged MOF was reacted with azides
introduced from the external solution. A strong fluorescence was observed only on
the surface of the MOF after the treatment of the azide with ethidium bromide as a
fluorophore. As another example, the surface hydrophilicity and wettability of the
MOF could be changed by employing CuAAC with the azide-terminated polyethylene glycol (PEG). Subsequently, the same authors synthesized the core-shell MOF
modified with two different azides by controlling the deprotecting reagents of the
TMS-protected alkyne-tagged MOF [28]. In the multiple deprotection and CuAAC,
the crystallinity and the nanoporous structure of the MOF were well maintained.
Since the organic ligand having an azide group is not commercially available for
the PSM of the MOF, it is necessary to synthesize them through the several steps of
organic reactions. This should be a drawback for the CuAAC for the PSM. In 2010,
Farrusseng and colleagues reported a one-pot, two-step PSM from aminoterephthalic
acid as the common starting material by the direct conversion of the amino group
to the azide group [29] (Scheme 25.2c). They first prepared a series of MOF, called
DMOF-NH 2 and MIL-68(In)-NH 2 . The PSM of the amino group to the azide group in
the MOF was then done by the treatment of nitrite tert-butyl and trimethylsilylazide
in a THF solution at room temperature, followed by the CuAAC with the terminal
alkynes in the presence of copper (I) hexafluorophosphate. The resulting MOF was
achieved by quantitative modification of the organic ligand. The surface area of
the pores by this modification was reduced to 9–18% of the original MOF, and the
pore volume by 6–14%. This method is applicable to other MOF such as IRMOF3, MIL-101-NH 2 , CAU-1, and MIL-53 providing many functional modified MOF.
They also demonstrated that a large number of alkynes, such as phenylacetylene,
propargylamine, 1-hexyne, propargyl alcohol, and propiolic acid, can be used to
react with the MOF. Since the first step has a low efficiency due to the low diffusion
rate in the nanopores, a high excess amount of trimethylsilylazide should be required
for the quantitative conversion. Some limitation to the type of functional groups of the