Chemistry Reference
In-Depth Information
Fig. 3.27
X-ray crystal structures of the Q[6]/Cd
2
+
-based compound:
a
and
b
the coordination
feature of Cd
2
+
cations with cucurbituril;
c
the Cd
2
(
ʼ
-Cl)
2
Cl
2
(H
2
O)
3
complex;
d
and
e
a coordi-
nated cucurbituril surrounded by six coordinated cucurbiturils through the Cd
2
(
ʼ
-Cl)
2
Cl
2
(H
2
O)
3
complexes;
f
an overall view of the arrangement of the coordinated cucurbiturils and Cd
2
(
ʼ
-
Cl)
2
Cl
2
(H
2
O)
3
complexes
the two Cd
2
+
cations (2Cd1) in the Cd
2
(
ʼ
-Cl)
2
Cl
2
(H
2
O)
3
complex. Each Cd
2
(
ʼ
-
Cl)
2
Cl
2
(H
2
O)
3
complex can link two neighboring cucurbituril molecules. Thus,
at each portal of the cucurbituril molecule, three Cd
2
+
cations (Cd1) from three
Cd
2
(
ʼ
-Cl)
2
Cl
2
(H
2
O)
3
complexes coordinate to three portal carbonyl oxygens alter-
natively, and each cucurbituril molecule can link six such coordinated cucurbituril
molecules (Fig.
3.27
d, e). Figure
3.27
f shows an overall view of the arrangement
of coordinated Q[6] molecules and Cd
2
(
ʼ
-Cl)
2
Cl
2
(H
2
O)
3
complexes. Although
KCl was added to the synthetic system, K
+
was not observed in the obtained com-
pound. Nevertheless, the presence of potassium cations could influence the coor-
dination and supramolecular assembly of Q[6] molecules and Cd
2
+
ions. In HCl
solution, Cd
2
+
produces [CdCl
4
]
2
−
anions that form the Cd honeycomb, which are
filled with the tubular Cd
2
+
-cucurbituril coordination polymers [
47
].
3.4 Induced Coordination Polymers of Cucurbit[7]uril
with Metal Ions
In cucurbiturils-based coordination chemistry, it seems that the coordination
of Q[
n
,
n
≥
7]s with metal ions seems to be more difficult than that of Q[5] or
Q[6] with metal ions. It is likely that the larger portal size of Q[
n
,
n
≥
7]s causes
a wider distribution of the carbonyl oxygens, resulting in difficulty in the effec-
tive coordination of Q[
n
,
n
≥
7] with metal ions. However, recent works reveal
that the Q[7] molecule may also readily coordinate to metal ions and form novel
polydimensional coordination polymers in the presence of the structure directing
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