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Fig. 3.13
X-ray crystal structure of
a
samarium cation/cucurbit[5]uril pair linked by a
[Sm(H
2
O)
4
]
3
+
cation through direct coordination;
b
the network constructed of the Q[5] pairs;
c
stacking of the networks filled with nitrate anions
in the formation of a 2D network. Figure
3.14
b shows the detailed coordination
of Q[5] with Nd
3
+
cations. On the other hand, the [ZnCl
4
]
2
−
anions, formed from
Zn
2
+
cations in HCl solution, are found in association with a distorted honey-
comb-like framework (Fig.
3.14
c) in which the Nd/Q[5]-based linear coordination
polymers are filled in the cells (Fig.
3.14
d, e). Electrostatic interactions between
the Nd
3
+
/Q[5] complex cations and the surrounded [ZnCl
4
]
2
−
anions could be
driving forces resulting in the formation of the Nd
3
+
/Q[5]-based supramolecular
assembly.
In recent years, our lab investigated the coordination of metal ions to perhyd
roxycucurbit[
n
]urils {(HO)
2
n
Q[
n
]s}, which can offer not only portal carbonyl
oxygens but also the equatorial hydroxyl groups (another kind of self-struc-
ture directing agent) as binding sites to metal ions to assemble polydimensional
coordination polymers (Fig.
3.15
, left). For examples, two novel 2D coordina-
tion polymers were obtained by reactions of alkali metal (K
+
and Cs
+
) salts with
perhydroxycucurbit[5]uril, {(HO)
10
Q[5]}, and their structures were determined
by single-crystal X-ray diffraction studies [
38
]. Structure analysis revealed that
the (HO)
10
Q[5] ligands are interlinked into 2D networks through coordination of
their carbonyl groups and hydroxyl groups to the alkali metal ions (K
+
and Cs
+
)
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