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with that obtained from the anion derived from 2-pyridylacetic acid (HPA). The
crystal structure of the Q[6]/Eu
3
+
/AP
−
complex shows that the Q[6] molecule
coordinates with a Eu
3
+
cation, and includes the aromatic moiety of the organic
guest. Moreover, the anion moiety (COO
−
) of the guest further coordinates to
the capped Eu
3
+
cation, resulting in the formation of the typical organic-guest-
induced Q[6]/metal complex (Fig.
2.21
f) [
54
].
Using a hydrothermal method, Thuéry obtained some simple Q[6]/UO
2
2
+
complexes by combination of Q[6] and UO
3
or UO(NO
3
)
2
6H
2
O in the pres-
ence of perrhenic acid and formic acid, respectively [
55
]. The crystal structure of
the complex with perrhenic acid shows a dinuclear species in which one uranyl
ion is bound to each Q[6] portal through bidentate coordination, to one perrhen-
ate ion located
trans
with respect to the macrocycle, and to half a perrhenate ion,
which occupies the same coordination site as an aqua ligand. Both are given occu-
pancy parameters of 0.5 (Fig.
2.22
a) [
55
]. The crystal structure of the complex
with sebacic acid shows uranyl coordination by Q[6]. Each U1 atom is bound to
two carbonyl atoms from two Q[6] molecules, which are adjacent in its equatorial
plane. The average length of such bond is 2.38(4) Å, in agreement with the aver-
age value of 2.36(4) Å for urea derivatives reported in the Cambridge Structural
Database (CSD) (Fig.
2.22
b) [
56
]. Heterometallic Q[
n
]-based complexes com-
monly feature coordination of two different metal ions at both portals of the Q[
n
]
molecule. Thuéry demonstrated an unusual case in which a series of novel het-
erometallic uranyl-lanthanide molecular complexes (Q[6]/UO
2
2
+
/Ln
3
+
, Ln
=
Sm,
Eu, Gd, Lu) are obtained from the reaction of uranyl and lanthanide nitrates with
Q[6] in the presence of perrhenic acid under hydrothermal conditions. Both metal
cations of UO
2
2
+
and Ln
3
+
are bound to carbonyl groups of the same Q[6] portal
(Fig.
2.22
c) [
57
].
Fig. 2.22
X-ray crystal structures of two Q[6]/UO
2
2
+
complexes formed in the presence of
a
perrhenic acid;
b
formic acid; and
c
the heterometallic Q[6]/UO
2
2
+
/Ln
3
+
complexes
(Ln
=
Sm, Eu, Gd, Lu)
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