Chemistry Reference
In-Depth Information
Fig. 2.23
X-ray structure
of the isomorphous
heterometallic complexes
of type [UO
2
Ln(Q[6])
(ReO
4
)
2
(NO
3
)(H
2
O)
7
]
(Ln
=
Sm, Eu, Gd, Lu),
shown for Ln
=
Sm
Initial attempts by Thuéry to prepare heteronuclear uranyl-lanthanide Q[6]
complexes were unsuccessful [
27
]. However, four such species of type [UO
2
Ln(Q[6])
(ReO
4
)
2
(NO
3
)(H
2
O)
7
](ReO
4
)
2
(Ln
=
Sm, Eu, Gd, Lu) were subsequently isolated
following reaction of a mixture of uranyl nitrate and lanthanide nitrate with Q[6] in
the presence of [ReO
4
]
−
under hydrothermal conditions [
57
]. In an unusual arrange-
ment both the UO
2
2
+
and Ln
3
+
cations bind to carbonyl groups on the
same
Q[6]
portal (Fig.
2.23
). The UO
2
2
+
also binds to a monodentate [ReO
4
]
−
group as well as
to three waters while the Ln
3
+
binds to a monodentate [ReO
4
]
−
and a nitrato ligand
together with four waters, with the latter [ReO
4
]
−
included in the Q[6] cavity. This
was the first reported example of the inclusion of a tetrahedral oxoanion in Q[6].
In a subsequent study it was shown that UO
2
2
+
combined with Nd
3
+
, Dy
3
+
,
Er
3
+
, or Yb
3
+
nitrate in each case reacts with Q[6] and 1,2-ethanedisulfonate
(EDS
2
−
) under hydrothermal conditions to yield heterometallic complexes of type
[(UO
2
)
4
Nd
2
(EDS)
4
(OH)
4
(Q[6])(H
2
O)
16
](NO
3
)
2
8H
2
O, and [(UO
2
)
2
Ln
1.5
(EDS)
2
(OH)
2
(NO
3
)
1.5
(Q[6])(H
2
O)
7.5
][(UO
2
)
2
(EDS)-(OH)
2
(H
2
O)
4
]NO
3
5.5H
2
O (where
Ln
=
Dy, Er and Yb) [
58
]. In each complex the Ln
3
+
ion is bound to a Q[6] and
partially caps a portal. Each EDS
2
−
co-ligand binds to a UO
2
2
+
and an Ln
3
+
ion
via its two sulfonate groups in a bis-monodentate manner, with the UO
2
2
+
ion
also being part of a bis(hydroxide)-bridged dinuclear unit that forms part of a
link between adjacent Q[6] units such that each complex adopts a ribbon-like 1D
assembly.
In summary, unlike in the coordination of Q[5] with the metal ions, a wider
bonding site distribution is available because of the larger portal size of Q[6]s.
With such distribution, the metal ion can generally coordinate to one to three por-
tal carbonyl oxygens, and more than one metal ion may be located at the same
portal of a Q[6] molecule.
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