Chemistry Reference
In-Depth Information
Fig. 35 X-ray structure of non-IPR
#11188
C
72
Cl
4
.(a) Fused pentagons are shown in
blue
.(b)
Schlegel diagram showing the position of the four chlorine atoms. (Reprinted with permission
from [
279
].)
Particular attention has been devoted to the structure of fullerene C
72
, a so-called
“missing fullerene” because empty C
72
, IPR or non-IPR isomer, had never been
isolated. However, along with further studies, recently several C
72
-based species
have been successfully prepared and characterized, namely La
2
@D
2
(10611)-C
72
[
275
], Ce
2
@D
2
(10611)-C
72
[
276
], La@C
2
(10612)-C
72
[
277
], and Sc
2
S@Cs
(10528)-C
72
[
278
].
Experimental results have recently reported, for the first time, the higher stability
of a non-IPR fullerene compared to its related IPR isomer for C
72
Cl
4
[
279
,
280
]
(Fig.
35
). These new results violate the “universal” IPR rule for fullerenes, but
confirm the valuable “strain-release” and “local aromaticity” principles that have
been so useful to predict the stability of a wide variety of fullerene derivatives. The
IPR rule is therefore valid for pristine fullerenes, whereas for fullerene derivatives
additional factors emerge that could eventually force a non-IPR cage to be the most
stable one. These new results pave the way to the advent of a huge family of, so far,
unknown non-IPR fullerenes whose number would be almost infinite. These ther-
modynamically less stable carbon cages should exhibit significant differences
compared to those IPR obeying fullerenes, thus enhancing the properties and
applications of these molecular allotropes of carbon. The scientific community
should be ready for the advent of the unprecedented non-IPR fullerenes, the
fullerenes for the near future!
8 Summary, Conclusions, Outlook
In the above sections we have presented some of the important achievements in the
past few years with buckyballs from the viewpoint of a synthetic chemist and with
an eye on the most remarkable properties of these molecules of interest for practical
purposes, namely in organic electronics.
