Chemistry Reference
In-Depth Information
highly disordered, but 1,2,5,6-tetrabromocorannulene (18) has perfect columnar
order in Type A [
39
].
Although all four packing types have bowl-in-bowl stacks, the factors necessary
to control the orientations of neighboring columns are still not well known. Even
the same compound packs in different crystal systems. Trigonal crystals of
hemibuckminsterfullerene (145-
t
) show as Type A, whereas orthorhombic crystals
of hemibuckminsterfullerene (145-
o
) present as Type quasi B.
In contrast to the packing types described above, several compounds, such as
pentakis(phenylthio)corannulene 48 (XR
¼
SPh) (Siegel et al., unpublished results),
pentaarylcorannulenes 50 (R
¼
manisyl, 2,6-C
6
H
3
Cl
2
)[
70
,
180
], decaarylcorannulene
57 (R
4-C
6
H
4
Cl) [
74
], and decakis(phenylthio)corannulene 58a [
75
], have bulky
substituents at rim positions, which avoid the intermolecular interaction between
any two corannulyl cores. Equally notable is that, unlike tetrakis(arylethynyl)
corannulenes 41 and pentakis(arylethynyl)corannulenes 49 [
39
], decakis
(1-pentynyl)corannulene (55)[
73
] does not present column-type packing. Although
these compounds do not conform to the model bowl-in-bowl packing motif, some of
them can furnish polar crystals. For example, pentamanisylcorannulene 50 [
70
]and
decakis(1-pentynyl)corannulene (55)[
73
] form polar crystals as defined by their
space groups of
P
1
and
P
n
,respectively.
¼
9 Conclusion and Outlooks
The syntheses, structures, and properties of buckybowls are highly interesting
topics, and numerous scientists have been motivated to join the field. In comparison
with our previous review article in 2006, investigations of buckybowls are full of
vitality and many important achievements have been presented in the past 8 years.
Corannulene is the seed of buckybowl chemistry; its preparation has been
improved from the milligram to the kilogram scale, and reactions have been
conducted under mild conditions in the solution phase, in which many functional
groups are tolerated. With these advantages, many corannulenyl derivatives and
more expanded bowl-shaped molecules can easily be made for various studies.
Thanks to the new synthetic protocols, many highly curved fragments of C
60
,C
70
and higher fullerenes were synthesized, but improvements of reaction efficiency are
still tough challenges for synthetic chemists. It must be emphasized that the devel-
oped synthetic strategies for generating buckybowls provide a reasonable basis for
routes to furnish carbon tubes with homogenous molecular weight distributions.
The correlations between structures and bowl-to-bowl inversion barriers provide
information on the inversion dynamics and design of a static bowl. Increase in the
curve of buckybowls may also increase their molecular dipole moment. A high
inversion barrier conveys a configurational stability to a chiral buckybowl, avoiding
loss of enantiopurity through the bowl-inversion racemization process.
The presence of convex and concave surfaces in
-bowls causes the molecular
packing complex. Control of their crystal packing to form polar crystals is
π
