234
H. Ohtsu et al.
surfaces of crystals, respectively. The presence of surface-confined iodine could not
be avoided because the reaction produces two additional equivalents of I 2 which
escapes the pores. The elemental analysis results determined the chemical formula
of the network product to be [(ZnBr 2 ) 3 (TPT) 2 (I 2 )](I 2-surface ) 0.67 . The iodine loading
was also quantified by TGA, which showed a two-step weight loss. The first step
corresponds to desorption of I 2 from the particle surface, whereas the second one
corresponds to the loss of I 2 from the pores. The overall weight decrease below
575 K was approximately 25.3%, which agrees with the total iodine content (24.6%)
calculated from the molecular formula, [(ZnBr 2 ) 3 (TPT) 2 (I 2 )](I 2-surface ) 0.67 . The I 2 in
the pore interacts with the Br
− sites of the network. The I· · · Br distance is 3.61 Å,
which is shorter than the sum of the individual van der Waals radii of I and Br
(3.75 Å) [74]. Also, the I–I–Br angle is 153° (non-linear), indicating mainly a π-type
interaction combined with some contribution of σ-type interactions. The appearance
of absorption band at 280 nm can be attributed to a strong charge-transfer interaction
between Br
− and I 2 . This band was not clearly observed in the [(ZnI 2 ) 3 (TPT) 2 ]
network containing encapsulated I 2 , indicating that only σ-type interactions occur
between I
− sites of the network and the guest I 2 . The brominated network shows
significantly stronger affinity for I 2 because of the additional contribution of πinteractions which are absent in the iodine analogue.
This post-synthetic modification of the pore is due to the strong oxidative ability
of Br 2 . The oxidation potential of Br 2 /Br
− redox couple is 1.087 V versus SHE,
which is higher than that for the I 2 /I
− couple, 0.54 V versus SHE. Therefore, the
encapsulated of Br 2 readily oxidizes the constituent I
− to give I 2 . This type of postsynthetic reaction is the first example of redox induced ligand transformation, which
results in a network component replacement. The resulting pore modification enables
the dramatic changes in the properties of interactive sites by switching from I
− to
Br
− .
Furthermore, thermal treatment of the I 2 encapsulated ZnBr network led to the
guest removal affording an activated structure. When the I 2 loaded [(ZnBr 2 ) 3 (TPT) 2 ]
network was heated at 573 K, the powder turned white, which is a sign of the release of
I 2 molecules from the pores. The ab initio PXRD structural analysis of the remaining
white powder revealed it to be isostructural with the starting [(ZnI 2 ) 3 (TPT) 2 ] network
(Fig. 12.11). The pore window of the bromine structure is 2.6 × 4.6 Å, which is larger
compared to the iodide analogue because of the smaller ionic radius of Br
− relative
to I
− . The halide replacement retained the overall saddle-type network structure and
preserved the topology. The same structure could not be obtained starting directly
from ZnBr 2 and TPT, either using a solution-phase synthesis or by crystallization
from vapor. In both cases, the interpenetrating network was the predominant product.
As a result, the only available synthetic route toward the [(ZnBr 2 ) 3 (TPT) 2 ] material
is through oxidative encapsulation and ligand replacement with Br 2 . The resultant
bromide network was found to be stable up to 673 K under N 2 , as confirmed by TGA
measurements.
Due to the presence of Br
− ions as interactive pore sites, the trapping of Br 2 was
attempted. For these experiments, the Br 2 vapor diffusion was also performed under
the same conditions as those used for the Br 2 encapsulation into [(ZnI 2 ) 3 (TPT) 2 ].
H. Ohtsu et al.
surfaces of crystals, respectively. The presence of surface-confined iodine could not
be avoided because the reaction produces two additional equivalents of I 2 which
escapes the pores. The elemental analysis results determined the chemical formula
of the network product to be [(ZnBr 2 ) 3 (TPT) 2 (I 2 )](I 2-surface ) 0.67 . The iodine loading
was also quantified by TGA, which showed a two-step weight loss. The first step
corresponds to desorption of I 2 from the particle surface, whereas the second one
corresponds to the loss of I 2 from the pores. The overall weight decrease below
575 K was approximately 25.3%, which agrees with the total iodine content (24.6%)
calculated from the molecular formula, [(ZnBr 2 ) 3 (TPT) 2 (I 2 )](I 2-surface ) 0.67 . The I 2 in
the pore interacts with the Br
− sites of the network. The I· · · Br distance is 3.61 Å,
which is shorter than the sum of the individual van der Waals radii of I and Br
(3.75 Å) [74]. Also, the I–I–Br angle is 153° (non-linear), indicating mainly a π-type
interaction combined with some contribution of σ-type interactions. The appearance
of absorption band at 280 nm can be attributed to a strong charge-transfer interaction
between Br
− and I 2 . This band was not clearly observed in the [(ZnI 2 ) 3 (TPT) 2 ]
network containing encapsulated I 2 , indicating that only σ-type interactions occur
between I
− sites of the network and the guest I 2 . The brominated network shows
significantly stronger affinity for I 2 because of the additional contribution of πinteractions which are absent in the iodine analogue.
This post-synthetic modification of the pore is due to the strong oxidative ability
of Br 2 . The oxidation potential of Br 2 /Br
− redox couple is 1.087 V versus SHE,
which is higher than that for the I 2 /I
− couple, 0.54 V versus SHE. Therefore, the
encapsulated of Br 2 readily oxidizes the constituent I
− to give I 2 . This type of postsynthetic reaction is the first example of redox induced ligand transformation, which
results in a network component replacement. The resulting pore modification enables
the dramatic changes in the properties of interactive sites by switching from I
− to
Br
− .
Furthermore, thermal treatment of the I 2 encapsulated ZnBr network led to the
guest removal affording an activated structure. When the I 2 loaded [(ZnBr 2 ) 3 (TPT) 2 ]
network was heated at 573 K, the powder turned white, which is a sign of the release of
I 2 molecules from the pores. The ab initio PXRD structural analysis of the remaining
white powder revealed it to be isostructural with the starting [(ZnI 2 ) 3 (TPT) 2 ] network
(Fig. 12.11). The pore window of the bromine structure is 2.6 × 4.6 Å, which is larger
compared to the iodide analogue because of the smaller ionic radius of Br
− relative
to I
− . The halide replacement retained the overall saddle-type network structure and
preserved the topology. The same structure could not be obtained starting directly
from ZnBr 2 and TPT, either using a solution-phase synthesis or by crystallization
from vapor. In both cases, the interpenetrating network was the predominant product.
As a result, the only available synthetic route toward the [(ZnBr 2 ) 3 (TPT) 2 ] material
is through oxidative encapsulation and ligand replacement with Br 2 . The resultant
bromide network was found to be stable up to 673 K under N 2 , as confirmed by TGA
measurements.
Due to the presence of Br
− ions as interactive pore sites, the trapping of Br 2 was
attempted. For these experiments, the Br 2 vapor diffusion was also performed under
the same conditions as those used for the Br 2 encapsulation into [(ZnI 2 ) 3 (TPT) 2 ].