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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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