188
N. Tohnai
building blocks for fabrication of the diamondoid network (Fig. 10.1a). Tetrahedral supramolecules are expected to act as sterically bulky nodes that prevent the
diamondoid network from forming a highly interpenetrating structure. Previously,
a specific type of supramolecule was also reported, termed a [4 + 4] supramolecular cluster. This compound was made of organic salts comprising triphenylmethylamine (TPMA) and monosulfonic acid derivatives (Fig. 10.1b, i). Within these clusters, the sulfonic acid derivatives are always arranged in tetrahedra as a result of
cubic charge-assisted hydrogen bonding. Specific tetrahedral supramolecular clusters were designed that combined TPMA and monosulfonic acid derivatives with
polycyclic aromatic moieties to produce diamondoid networks. In these substances,
the long aromatic moieties protruding in the tetrahedral direction also function as
a supramolecular adhesive that connects clusters via π-π interactions [12], thus
generating not only rigid but also flexible (amphoteric) diamondoid networks and
porous structures. These amphoteric structures are expected to provide more static
and dynamic responses to external stimuli than are obtained with some flexible
MOFs [2b, c, 3c]. Furthermore, the size, shape, and functionality of the clusters are
dependent on the specific sulfonic acid derivative employed. In the present work,
three different sulfonic acid derivatives were combined with TPMA: naphthalene2-sulfonic acid (2-NS, 1), anthracene-2-sulfonic acid (2-AS, 2) [13], and pyrene-1sulfonic acid (1-PyS, 3) [14] (Fig. 10.1b, ii). Organic salts containing either 2-AS
or 1-PyS were used to construct diamondoid networks and interpenetrated porous
structures containing aromatic molecules as templates. Interestingly, the degree of
interpenetration of these diamondoid networks can be controlled by adjusting the
bulkiness of the clusters, resulting in the formation of voids with various sizes and
dimensions. In addition, the 2-AS diamondoid network changes structure depending
on the ratio of pores to template molecules and the type of template.
10.2 Hierarchical Construction of d-POSs
The organic salts made by combining 2-AS and TPMA in the present work were
recrystallized from a mixture of ethanol and nonpolar solvents such as aromatic
hydrocarbons and appeared as yellow crystals. Single crystals suitable for single
X-ray crystallographic analysis were obtained by recrystallization from a mixture of
ethanol and 1,2,4-trichlorobenzene (TCB) [15]. This crystallographic analysis established that the crystals had a porous structure based on a diamondoid network, and
so the materials produced in this work are generally referred to herein as diamondoid POSs (d-POSs) (specifically, d-POS-2a, Fig. 10.2a). Figure 10.2c illustrates
the manner in which the d-POS-2a structure was built hierarchically, starting with
2-AS and TPMA (Fig. 10.2c). In the first step, the 2-AS and TPMA are assembled
into [4 + 4] supramolecular clusters due to the effects of charge-assisted hydrogen
bonding. The length of the hydrogen bond between the oxygen atom of the 2-AS
and the nitrogen atom of the TPMA ranged from 2.735 to 2.863 Å (Fig. 10.3a).
These hydrogen bonds produced a cubic network. However, because the anthracenyl
N. Tohnai
building blocks for fabrication of the diamondoid network (Fig. 10.1a). Tetrahedral supramolecules are expected to act as sterically bulky nodes that prevent the
diamondoid network from forming a highly interpenetrating structure. Previously,
a specific type of supramolecule was also reported, termed a [4 + 4] supramolecular cluster. This compound was made of organic salts comprising triphenylmethylamine (TPMA) and monosulfonic acid derivatives (Fig. 10.1b, i). Within these clusters, the sulfonic acid derivatives are always arranged in tetrahedra as a result of
cubic charge-assisted hydrogen bonding. Specific tetrahedral supramolecular clusters were designed that combined TPMA and monosulfonic acid derivatives with
polycyclic aromatic moieties to produce diamondoid networks. In these substances,
the long aromatic moieties protruding in the tetrahedral direction also function as
a supramolecular adhesive that connects clusters via π-π interactions [12], thus
generating not only rigid but also flexible (amphoteric) diamondoid networks and
porous structures. These amphoteric structures are expected to provide more static
and dynamic responses to external stimuli than are obtained with some flexible
MOFs [2b, c, 3c]. Furthermore, the size, shape, and functionality of the clusters are
dependent on the specific sulfonic acid derivative employed. In the present work,
three different sulfonic acid derivatives were combined with TPMA: naphthalene2-sulfonic acid (2-NS, 1), anthracene-2-sulfonic acid (2-AS, 2) [13], and pyrene-1sulfonic acid (1-PyS, 3) [14] (Fig. 10.1b, ii). Organic salts containing either 2-AS
or 1-PyS were used to construct diamondoid networks and interpenetrated porous
structures containing aromatic molecules as templates. Interestingly, the degree of
interpenetration of these diamondoid networks can be controlled by adjusting the
bulkiness of the clusters, resulting in the formation of voids with various sizes and
dimensions. In addition, the 2-AS diamondoid network changes structure depending
on the ratio of pores to template molecules and the type of template.
10.2 Hierarchical Construction of d-POSs
The organic salts made by combining 2-AS and TPMA in the present work were
recrystallized from a mixture of ethanol and nonpolar solvents such as aromatic
hydrocarbons and appeared as yellow crystals. Single crystals suitable for single
X-ray crystallographic analysis were obtained by recrystallization from a mixture of
ethanol and 1,2,4-trichlorobenzene (TCB) [15]. This crystallographic analysis established that the crystals had a porous structure based on a diamondoid network, and
so the materials produced in this work are generally referred to herein as diamondoid POSs (d-POSs) (specifically, d-POS-2a, Fig. 10.2a). Figure 10.2c illustrates
the manner in which the d-POS-2a structure was built hierarchically, starting with
2-AS and TPMA (Fig. 10.2c). In the first step, the 2-AS and TPMA are assembled
into [4 + 4] supramolecular clusters due to the effects of charge-assisted hydrogen
bonding. The length of the hydrogen bond between the oxygen atom of the 2-AS
and the nitrogen atom of the TPMA ranged from 2.735 to 2.863 Å (Fig. 10.3a).
These hydrogen bonds produced a cubic network. However, because the anthracenyl