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Fig. 2.25
X-ray crystal structures of two different Q[8]/Metal complexes
a
Q[8]/Sr
2
+
complex
and
b
Q[8]/Bi
3
+
complex
+
complex and
b
tQ[14]/Eu
3
+
Fig. 2.26
X-ray crystal structures of
a
the Q[5]@Q[10]/K
and characterized by X-ray diffraction in the early development of cucurbituril
chemistry. One was obtained by slow concentration of aqueous solutions contain-
ing strontium nitrate and Q[8]. The crystal structure of this Q[8]/Sr
2
+
complex
shows that each Q[8] molecule is bound to four strontium cations (two cations per
each portal), and the strontium atoms linked to the portal of the larger macrocycle
are remote from each other and are not linked to each other through the bridging
ligands (Fig.
2.25
a) [
60
]. The other Q[8]/metal-based coordination complex was
obtained by reacting Bi(NO
3
)
3
with Q[8] in 3M HNO
3
. This complex has a Q[8]
molecule coordinated by two [Bi(NO
3
)(H
2
O)
5
]
2
+
fragments (Fig.
2.25
b) [
61
].
Cucurbit[10]uril (Q[10]), which was discovered by Day in 2002, used to be
the largest member in the Q[
n
] family. However, it is rare to see a simple com-
plex of Q[10] or its derivatives [
4
,
62
,
63
] with metal ions not only because Q[10]
itself is rare, but also because of the wider carbonyl oxygen distribution. A host-
guest/M
n
+
complex, Q[5]@Q[10]/K
+
was synthesized by Liu and coworkers
(Fig.
2.26
a) [
64
]. A Q[5] molecule is included in the cavity of Q[10], and two K
+
cations, each of which does not fully cover portal of Q[5] molecule, coordinates
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