Chemistry Reference
In-Depth Information
Table 8 Molecular packing of buckybowls
Type Compounds
A 2 [
136
], 18 [
39
], 103a [
128
], 123 [
140
], 145-
t
[
159
], 155 [
167
]
Quasi-A -Ph [
39
], 101a [
128
], 104 [
89
], 111-Me [
132
], 151 [
162
,
164
], 153 (R
¼
H) [
162
],
161-H [
170
], 166 [
177
]
B
21c [
40
], 23c [
41
], 41 (R
¼
3,5-C
6
H
3
(CH
3
)
2
)[
39
], 45-CF
3
[
81
], 98 [
128
], 101b [
128
],
103b [
128
] 129 [
152
]
Quasi-B -F [
40
], 28-Cl [
40
], 49 (R
¼
3,5-C
6
H
3
(CH
3
)
2
)[
39
], 81-C
6
F
5
[
110
], 100 [
27
],
102 [
89
], 145-
o
[
159
]
m
>0
m
=0
m
>0
m
=0
A
B
quasi A
quasi B
Scheme 56 Schematic presentations of open geodesic bowls in crystals
8 Molecular Packing of Bowls in the Solid State
The curvature of buckybowls makes their solid-state packing very interesting but
complex. Buckybowls can be polar because of the different electronic distributions
within a curved surface [
179
]. Studies of the intermolecular interactions would be
useful to clarify the generation of polar crystals by controlling solid-state packing.
This kind of crystal engineering would allow buckybowls to make key advance-
ments in materials chemistry. The types of molecular packing are summarized in
Table
8
and Scheme
56
. The ideal model for applications in materials science is
Type A, bowl-in-bowl stacks where all columns are oriented toward the same
direction, resulting in polar crystals. Similar to Type A, crystals of Type Quasi-A
are also polar, but the bowls are slipped slightly from side to side within each stack.
In contrast, crystals of Types B and Quasi-B are apolar because the neighboring
columns are oriented toward opposite directions although they have bowl-in-bowl
stacks.
In principle, all four packing types in Scheme
56
have bowl-in-bowl stacks. The
molecule packing appears to depend on the size of the bowl surface area and the
depth of the bowl, with larger and deeper favoring 1D columns, which would be
encouraged to form by strong intermolecular interactions. As the aromatic molec-
ular surface area becomes smaller, the molecular packing changes away from
columnar. Recently, a theoretical investigation indicates that the dipole moment
of a buckybowl should be an important factor to yield 1D columnar stacks [
182
]. It
should also be noted that the periphery substituents can strongly affect crystal
packing arrangements. For example, the molecular packing of corannulene is
