Chemistry Reference
In-Depth Information
2.3 Simple Coordination Complexes
of Cucurbit[
n
,
n
≥
7]urils with Metal Ions
A comparison of complexes of Q[
n
,
n
≥
7]s and Q[5 or 6]s shows that the coor-
dination of Q[
n
,
n
≥
7]s with metal ions is more difficult than that of Q[5 or 6]
with metal ions. Few of the simple complexes involving with Q[
n
,
n
≥
7]s have
been reported in Q[
n
]-based coordination chemistry. The larger portal size of Q[
n
,
n
≥
7]s result in an even wider distribution of the carbonyl oxygens, which may be
a reason for the difficulty in the coordination of Q[
n
,
n
≥
7] with metal ions. The
first crystal structures of Q[7]/metal-based coordination complexes were obtained
by Thuéry. He investigated the influence of perrhenate ions on the structure of lan-
thanide complexes with Q[
n
]s to further probe the properties of Q[
n
]s in perrhenate
encapsulation [
27
]. The compound has a very large assembly uniting two differ-
ent Q[7]/Yb
3
+
complexes: The first comprises two Q[7] molecules bridged by one
Yb
3
+
cation, with two partially included (but not coordinated) [Yb(ReO
4
)(NO
3
)
(H
2
O)
5
]
+
cations (Fig.
2.24
a). The second is built from one bidentate Q[7], one
coordinated cation that is disordered over two positions related by a mirror plane,
and one coordinated and included ReO
4
−
anion (Fig.
2.24
b). However, in the pres-
ence of CsNO
3
or aqueous formic acid, combination of Q[7] with UO
2
(NO
3
)
2
or
UO
3
can yield simple Q[7]/UO
2
2
+
complexes, as shown in Fig.
2.24
c, d, respec-
tively [
59
]. In both Q[7]/UO
2
2
+
complexes, the UO
2
2
+
cation coordinates one por-
tal carbonyl oxygen, and a pair of OH
−
anions link two UO
2
2
+
cations.
Even though more Q[8]/metal-based simple complexes have been reported,
only two typical Q[8]/metal-based coordination complexes have been synthesized
Fig. 2.24
X-ray crystal structures of
a
and
b
two different Q[7]/Yb
3
+
complexes and two
different Q[7]/UO
2
2
+
complexes in the presence of
c
CsNO
3
and
d
formic acid
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