Chemistry Reference
In-Depth Information
Fig. 2.2
Structures of five representative alkyl-substituted Q[5]s:
a
Me
10
Q[5];
b
DMeQ[5];
c
1,2,4-HMeQ[5];
d
PMeQ[5] and
e
CyH
5
Q[5]
Fig. 2.3
X-ray crystal structures of molecular capsules and molecular bowls of Q[5] with var-
ious metal ions:
a
alkali (K
+
);
b
alkaline earth (Ba
2
+
);
c
transition (Cd
2
+
); and
d
lanthanide
(La
3
+
) metal ions
(1,2,4-HMeQ[5]), pentamethylcucurbit[5]uril (PMeQ[5]), pentacyclopentanocuc
urbit[5]uril (CyH
5
Q[5]), and so on show no obvious difference in affinity to the
metal ions (Fig.
2.2
).
For example, a series of molecular capsules or molecular bowls of Q[5] with
various metal ions, including alkali (K
+
), alkaline earth (Ba
2
+
), transition (Cd
2
+
),
and lanthanide (La
3
+
) metal ions (Fig.
2.3
) [
17
,
18
]. Moreover, these Q[5]-based
complexes exhibited the remarkable property of encapsulating a negatively
charged ion. Its easy synthesis, rigid structure, and chemical and thermal stability
could make Q[5] very attractive for complexation of anions in aqueous solution
[
18
]. Further experiments reveal that Q[5] shows special selectivity for including
“naked” chloride anion or nitrate anion under certain conditions. The metal-free
host has been demonstrated to selectively include nitrate ion, whereas the lantha-
nide-capped molecular capsule showed preference toward the inclusion of chloride
ion (Fig.
2.4
) [
19
].
Our group synthesized complexes of alkyl-substituted Q[5]s (referring to
Fig.
2.2
) with various metal ions. Most of them were molecular bowls or molecu-
lar capsules. The metal ions included alkali [
12
,
13
], alkaline earth [
14
], transi-
tion [
15
], and lanthanide [
16
] metal ions. For example, we evaluated the effect of
a series of alkaline earth metal ions (Ca
2
+
, Sr
2
+
, and Ba
2
+
) on their complexes
with CyH
5
Q[5] by mixing their chloride salts with CyH
5
Q[5] [
20
]. The experi-
mental results revealed that coordination of CyH
5
Q[5]-based molecular capsules
Search WWH ::
Custom Search