Chemistry Reference
In-Depth Information
Fig. 24 Chemical structure of the exTTF-based macrocyclic hosts. Reprinted with permission
from [
173
]
There are many other examples of tweezer-like and macrocyclic hosts for
fullerenes, which we will not discuss in this chapter. The interested reader can
refer to more comprehensive reviews [
144
,
166
]. In this very brief account we
intended to outline general considerations regarding the design principles for the
construction of hosts for fullerenes, illustrating them with a few selected examples.
5 Endohedral Fullerenes: Improving Size, Shape,
and Electronic Properties
Almost immediately after the discovery of the fullerene family, scientists wondered
about the possibility of introducing different atoms and molecules into the carbon
cages and speculated about the new properties that the hybrid materials could
exhibit. This expectation, far from decreasing, is actually growing with the appli-
cation of these materials in different fields such as medicine or molecular electron-
ics [
174
]. The properties of endohedral fullerenes can easily be modified depending
upon the species entrapped and the fullerene cages. In this sense, endohedral
fullerenes are classified in two principal categories:
1.
Metallofullerenes
, which are those that contain elemental metals or their
combined forms
[
175
]. More specifically,
this
family includes
classical
metallofullerenes
, M@C
2
n
or M
2
@C
2
n
, with 60
2n
88 [
176
],
metallic
carbides
,M
2
C
2
@C
2
n
and M
3
C
2
@C
2
n
, where 68
2n
92 [
177
],
metallic
nitrides
,M
3
N@C
2
n
, with 68
96 [
178
], and, more recently,
metallic oxides
,
M
4
O
2
@C
80
[
179
]. These fullerenes are typically produced by laser-vaporization or
arc discharge techniques of graphite-metal oxides composite materials in the
atmosphere of certain gases [
180
].
2.
Fullerenes encapsulating small molecules
, such as noble gas atoms (helium,
neon, argon, krypton, and even xenon have been introduced inside fullerene cages),
which are obtained by treating the fullerene powder under forced conditions (650
C
2n
