10 The Design of Porous Organic Salts with Hierarchical Process
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to reduce the void volume. However, in this material, the characteristic arrangement
of template molecules is confined by the 1D voids formed by three interpenetrating
diamondoid networks. This 1D molecular array could result in unique properties
such as polarization performance and anisotropic charge conduction [17].
10.3 Structural Diversification of d-POSs with Variations
in the Sulfonic Acid
Similar to the organic salt containing 2-AS, organic salts composed of 1-PyS
and TPMA also formed a d-POS-2 type material through a similar hierarchical
process (Fig. 10.2b, d). Single crystals for X-ray crystallographic analysis were
obtained by recrystallization from a mixture of ethanol and 1,3,5-trimethylbenzene
(TMB). According to X-ray analysis, the 1-PyS and TPMA also formed tetrahedral
supramolecular clusters through charge-assisted hydrogen bonding (Fig. 10.2d), with
a maximum distance between adjacent sides of the clusters of approximately 25 Å.
The clusters were arranged in a diamondoid network by π-π stacking between the
pyrenyl groups and the resulting diamondoid network also contained large voids with
29 × 32 Å hexagonal windows, leading to an interpenetrating structure. However,
it should be noted that, unlike the three-fold interpenetration associated with the dPOS-2a, only two independent diamondoid networks penetrate one another in this
material. Therefore, there are 2D voids in the porous structure (Fig. 10.2b, right). The
1D voids having a maximum space of 7.1 × 5.1 Å and a minimum space of 5.7 ×
5.7 Å are connected by small orthogonal channels, and the calculated air gap volume
is 29%. The TMB molecules from the recrystallization solvent were contained in the
primary 1D voids and acted as templates. These void differences arise from variations in the shapes and sizes of the substituents in the sulfonic acid derivatives. The
maximum distance between the sulfur and carbon atoms in 1-PyS is 7.8 Å, which
is slightly less than that in 2-AS (Fig. 10.1b, ii). Therefore, the hexagonal windows
in the d-POS-3 diamondoid network were smaller than the hexagonal windows in
the d-POS-2a. In contrast, the width of 1-PyS is greater than that of 2-AS, and the
maximum distances between any two carbon atoms in these compounds were 4.9 and
2.8 Å, respectively (Fig. 10.1b, ii). Therefore, 1-PyS and TPMA form more sterically
bulky clusters than 2-AS and TPMA, preventing interpenetration more effectively
(Fig. 10.2d). These results show that the relative ratio of the cluster core diameter
to the polycyclic aromatic length has a significant effect on the avoidance of highly
interpenetrating structures. When the polyaromatic group is short and wide, the relative proportion of the cluster cores increases. As a result, the resulting tetrahedral
clusters exhibit increased steric hindrance and there is reduced interpenetration in
the diamondoid network. In contrast, the organic salt composed of 2-NS and TPMA
did not form a porous structure with a diamondoid network (Fig. 10.5). This difference can be attributed to the naphthyl groups of the 2-NS molecules (in which the
maximum distance between sulfur and carbon atoms is 6.7 Å), which are too short
191
to reduce the void volume. However, in this material, the characteristic arrangement
of template molecules is confined by the 1D voids formed by three interpenetrating
diamondoid networks. This 1D molecular array could result in unique properties
such as polarization performance and anisotropic charge conduction [17].
10.3 Structural Diversification of d-POSs with Variations
in the Sulfonic Acid
Similar to the organic salt containing 2-AS, organic salts composed of 1-PyS
and TPMA also formed a d-POS-2 type material through a similar hierarchical
process (Fig. 10.2b, d). Single crystals for X-ray crystallographic analysis were
obtained by recrystallization from a mixture of ethanol and 1,3,5-trimethylbenzene
(TMB). According to X-ray analysis, the 1-PyS and TPMA also formed tetrahedral
supramolecular clusters through charge-assisted hydrogen bonding (Fig. 10.2d), with
a maximum distance between adjacent sides of the clusters of approximately 25 Å.
The clusters were arranged in a diamondoid network by π-π stacking between the
pyrenyl groups and the resulting diamondoid network also contained large voids with
29 × 32 Å hexagonal windows, leading to an interpenetrating structure. However,
it should be noted that, unlike the three-fold interpenetration associated with the dPOS-2a, only two independent diamondoid networks penetrate one another in this
material. Therefore, there are 2D voids in the porous structure (Fig. 10.2b, right). The
1D voids having a maximum space of 7.1 × 5.1 Å and a minimum space of 5.7 ×
5.7 Å are connected by small orthogonal channels, and the calculated air gap volume
is 29%. The TMB molecules from the recrystallization solvent were contained in the
primary 1D voids and acted as templates. These void differences arise from variations in the shapes and sizes of the substituents in the sulfonic acid derivatives. The
maximum distance between the sulfur and carbon atoms in 1-PyS is 7.8 Å, which
is slightly less than that in 2-AS (Fig. 10.1b, ii). Therefore, the hexagonal windows
in the d-POS-3 diamondoid network were smaller than the hexagonal windows in
the d-POS-2a. In contrast, the width of 1-PyS is greater than that of 2-AS, and the
maximum distances between any two carbon atoms in these compounds were 4.9 and
2.8 Å, respectively (Fig. 10.1b, ii). Therefore, 1-PyS and TPMA form more sterically
bulky clusters than 2-AS and TPMA, preventing interpenetration more effectively
(Fig. 10.2d). These results show that the relative ratio of the cluster core diameter
to the polycyclic aromatic length has a significant effect on the avoidance of highly
interpenetrating structures. When the polyaromatic group is short and wide, the relative proportion of the cluster cores increases. As a result, the resulting tetrahedral
clusters exhibit increased steric hindrance and there is reduced interpenetration in
the diamondoid network. In contrast, the organic salt composed of 2-NS and TPMA
did not form a porous structure with a diamondoid network (Fig. 10.5). This difference can be attributed to the naphthyl groups of the 2-NS molecules (in which the
maximum distance between sulfur and carbon atoms is 6.7 Å), which are too short