Chemistry Reference
In-Depth Information
Fig. 4.3
X-ray crystal structure of a representative compound:
a
a Ce
3
+
/SPMeQ[5] com-
plex with an included chloride anion and cerium cations;
b
detailed interactions between
a Ce
3
+
/SPMeQ[5] complex and the surrounding eight [CdCl
4
]
2
−
anions;
c
an overall view of
the honeycomb-like supramolecular assembly constructed of Ce
3
+
/SPMeQ[5] complexes and
[CdCl
4
]
2
−
anions;
d
a channel in the assembly containing a Ce
3
+
/SPMeQ[5] complex chain;
e
detailed interactions between Ce
3
+
/SPMeQ[5] complexes and [CdCl
4
]
2
−
anions in the chain
methyl-substituted cucurbit[5]uril (SPMeQ[5]) derived from a 3
ʱ
-methyl-glycoluril
have been investigated. Single-crystal X-ray diffraction analysis revealed that the
SPMeQ[5] selectively interacts with certain lanthanide ions and forms a coordination
capsule where a chloride anion is included in the cavity of the SPMeQ[5] mole-
cule in the presence of [CdCl
4
]
2
−
(Fig.
4.3
). The Ln
3
+
cations which interact with
SPMeQ[5] are the four light lanthanides, La
3
+
, Ce
3
+
, Pr
3
+
, Nd
3
+
, while the remain-
ing lanthanide cations stay in solution under the same interaction conditions. These
results suggest that SPMeQ[5]-Ln(NO
3
)
3
-CdCl
2
-HCl systems could be useful for
the selective isolation of these light lanthanide cations from mixtures also contain-
ing heavier lanthanide cations. In order to confirm this suggestion, representative
Ln
3
+
light
−
Ln
3
heavy
−
SPMeQ[5]
−
CdCl
2
−
HCl
systems with 1:1 ratios were selected
for isolating lighter lanthanides, namely Pr
3
+
-Sm
3
+
, Pr
3
+
-Eu
3
+
, Pr
3
+
-Tb
3
+
, and
Pr
3
+
-Lu
3
+
systems. Energy dispersive spectrometry (EDS) showed that the crystals
obtained from these systems contained a high proportion of the lighter lanthanides
(almost 100 %) for the group with 1:1 of
Ln
3
+
light
:
Ln
3
heavy
ratios (Fig.
4.4
). These
experimental results suggest that this strategy could be really useful, and SPMeQ[5]
could be used for isolating lighter lanthanides from their heavier counterparts [
9
].
Similar properties can be found in various Q[6]s-Ln
3
+
interaction systems. As
previously mentioned, linear coordination polymers have been assembled from
lanthanide cations (Ln
3
+
) and cucurbituril (Q[6]) in the presence of [CdCl
4
]
2
−
or
[ZnCl
4
]
2
−
anions as inorganic structure directing agents in HCl solution [
10
]. X-ray
diffraction analysis has revealed honeycomb-patterned supramolecular assemblies, in
which [CdCl
4
]
2
−
or [ZnCl
4
]
2
−
anions form the honeycomb and the hexagonal cells
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