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Fig. 3.25
X-ray crystal structures of
a
a tubular coordination polymer constructed from alter-
nating Q[6] and units of three Na
+
cations;
b
a unit of three Na
+
cations;
c
a [CdCl
4
]
2
−
-Na
+
unit; and
d
the 2D network constructed from Q[6]/Na
+
-based 1D coordination polymers and
[CdCl
4
]
2
−
anions
through electrostatic interactions. Every two [CdCl
4
]
2
−
anions interact with two
sodium cations (Na1) belonging to the neighboring tubular polymers, as shown in
Fig.
3.25
c. This interaction results in the formation of a 2D network, as shown in
Fig.
3.25
d.
Earlier, we mentioned that DMF and Sr(NO
3
)
2
were added into the Q[6]-
UO
2
2
+
-H
2
Cn systems in order to enhance the solubility of the higher diacid and
Q[6] in the reaction medium and thus obtain the 2D network coordination poly-
mers. Without Sr(NO
3
)
2
, the Q[6]-UO
2
2
+
-H
2
C9-DMF system produces a novel
3D framework in which the layers are composed of uranyl clusters and C9 diacids,
as shown in Fig.
3.19
. These layers are bridged by Q[6] molecules (Fig.
3.26
a).
Such linkage can also be viewed as resulting from the bridging of the [(UO
2
)
4
O
2
(OH)
2
Q[6]]
2
+
chains by C9 dicarboxylate ligands (Fig.
3.26
b) [
43
]. Thus, the ten-
dency for uranyl ions to give planar or gently undulating ribbons or sheets appears
to match the propensity of Q[6] to fit between them.
In addition to the previous summary on 1D and 2D uranyl-based coordination
polymers, these results provide new examples of the potential of cucurbiturils as
uranyl complexants or as structure directing agents. The frameworks, sheets, or
columns readily formed by Q[6] appear to be particularly well suited to associate
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