Chemistry Reference
In-Depth Information
+
Fig. 3.1
Linear coordination polymer of Q[5]s and K
cations
up Q[5] and potassium chloride in 1.5 M hydrochloric acid, in which lidded Q[5]
molecules link to one another through coordination of their carbonyl groups to the
potassium cations in between (Fig.
3.1
) [
1
].
Compared to Q[5]-based coordination polymer, Q[6] offered more chances to
form linear coordination polymers due to the larger portals, which can attract more
than one metal ion at one portal. Mock and Freeman first characterized it in 1981,
although they did not give the structural details of the Q[6]/Ca
2
+
complex, and
instead focused on the remarkable structure of Q[6] itself [
2
]. Freeman described
this complex in his succeeding paper in 1984 [
3
]. In the Q[6]/Ca
2
+
complex, each
Ca
2
+
ion is coordinated to three carbonyl O atoms; two at a portal of one cage
and the third at a portal of an immediate neighboring Q[6] (Fig.
3.2
a). Thus, a
1D polymer is formed through direct coordination of Q[6] molecules and Ca
2
+
cations. Materials with tubular architectures have attracted considerable interest
in the areas of nanotechnology, molecular sieves, ion sensors, and fluidic trans-
port systems [
4
-
6
]. Q[
n
]s readily coordinate with various metal ions to form 1D
tubular polymers through direct coordination. The coordination of Q[6] with alkali
metal ions could result in common 1D coordination polymers in which every two
Q[6] molecules are linked by two alkali metal ions, and the two metal ions may be
bridged by sharing water molecules or not bridged (Fig.
3.2
b-d) [
7
-
9
]. In particu-
lar, the Q[6]/Rb
+
coordination polymer chains are arranged to form a honeycomb
structure with large linear hexagonal channels running parallel to the polymer
chains (Fig.
3.2
e, f).
When we summarized the simple coordination complexes of Q[6]s with metal
ions, we mentioned that the interaction of Q[6]s with transition metal salts formed
mainly adducts of Q[6] with metal aqua complexes [
10
]. It is even more rare to
observe the coordination polymers based on Q[6]s with transition metal ions.
An interesting exception was demonstrated by Liu and coworkers in 2009. They
chose the copper(II) ion, nitrate, and the weak-field ligand, chloride, to construct
transition metal cucurbituril-based coordination tubes. They obtained a 1D zig-
zag coordination polymer {[Cu(H
2
O)
4
Q[6]] (NO
3
)
2
8H
2
O}
n
, and the tubular
coordination polymer {[Cu(H
2
O)
2
Cl
2
Q[6]] 1/3 (H
2
O)
3
}
n
, and demonstrated
a means of enhancing the coordination ability of the terminal carbonyl group of
cucurbituril under the direction of coordination chemistry [
11
]. The zigzag 1D
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