Chemistry Reference
In-Depth Information
Fig. 3.21
X-ray crystal structure of the Q[6]/Sm
3
+
compound:
a
overall view of the coordina-
tion features and supramolecular assembly of the compound and the honeycomb-like framework
composed of [CdCl
4
]
2
−
anions;
b
a zigzag coordination polymer of Sm
3
+
cations and Q[6] mol-
ecules surrounded by the [CdCl
4
]
2
−
anions;
c
coordination of the Sm
3
+
cations to the portal car-
bonyl oxygens of the Q[6] molecules; and
d
interaction of the [CdCl
4
]
2
−
anions with the Q[6]
molecules
the Ln-Q[6]-[CdCl
4
]
2
−
systems. The [CdCl
4
]
2
−
anions appear to form a hon-
eycomb structure (Fig.
3.21
a), and the Sm
3
+
cations coordinate to neighboring
Q[6] molecules to form zigzag coordination polymers that insert into the chan-
nels of the honeycomb framework, such that each individual zigzag coordination
polymer is surrounded by [CdCl
4
]
2
−
anions (Fig.
3.21
b). The Sm
3
+
cations are
octacoordinated by eight oxygen atoms, namely, four carbonyl oxygen atoms from
two neighboring Q[6] molecules (O1, O2, O7, and O8) and four water molecules
(O1W, O2W, O3W, and O4W) (Fig.
3.21
c). The formation of the [CdCl
4
]
2
−
hon-
eycomb is a consequence of ion-dipole interaction between the portal carbonyl
carbon atoms of the Q[6] molecules as well as hydrogen bonding between the
chlorine atoms of the anions and methine groups on the surface of the Q[6] mol-
ecules. Moreover, the formation of the [CdCl
4
]
2
−
honeycomb is conducive to the
coordination of lanthanide cations to Q[6] molecules (Fig.
3.21
) [
41
]. Our recent
studies have revealed that most transition metal ions have similar functions in
the construction of polydimensional coordination polymers. Most importantly,
we want to note here is that the rapid precipitation of Ln
3
+
-Q[6]-[CdCl
4
]
2
−
or
[ZnCl
4
]
2
−
systems in which the Ln
3
+
are La, Ce, Pr and Nd cations [
41
]. It is
therefore believed that such approaches could offer an opportunity to separate the
light lanthanides cations from lanthanides.
Recently, we explored a simple way to isolate
i
Q[6] from normal Q[6] by using
a Dowex 50W 2-400(H) column. The subtle difference in electrostatic proper-
ties of the surfaces of
i
Q[6] and Q[6] result in significant differences in physical
and chemical properties so that
i
Q[6] can be isolated from major normal Q[6]
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