Chemistry Reference
In-Depth Information
Fig. 2.15
X-ray crystal structures of molecular capsules of
m
-HMeQ[6] with metal ions:
a
K
+
+
+
;
b
Rb
;
c
Cs
Fig. 2.16
X-ray crystal structure of the Sm
3
+
-Q[6] triple-decker sandwich
portal size with a portal radius of 3.3-3.4 Å. This radius is substantially longer
than the bond length range observed for Ln
3
+
-O
carbonyl
bonds: 2.223-2.478 Å. As
a consequence a single lanthanide cation is unable to coordinate simultaneously
to all six carbonyl oxygens lining a Q[6] portal; generally only one to three portal
carbonyl oxygens have been found to bind. In the above complex, each Sm
3
+
cat-
ion ion coordinates to two portal carbonyl oxygens from each of two Q[6]s, with
the average bond length being 2.401 Å; each metal center achieves 8-coordination.
In a further paper Fedin reported a systematic study of Q[6] coordination with
La
3
+
, Ce
3
+
, Gd
3
+
, Ho
3
+
, and Yb
3
+
nitrates or bromides in aqueous solution [
45
].
While Q[6] is not soluble in water, it readily dissolves on heating with a satu-
rated solution of the above Ln
3
+
salts. Seven complexes were isolated—the first
five were obtained from the corresponding Ln
3
+
nitrate salt while the remain-
ing two were from the corresponding bromide salt: (i) [Gd(NO
3
)(H
2
O)
4
(Q[6])]
(NO
3
)
2
7H
2
O, (ii) [Ho(NO
3
)(H
2
O)
4
(Q[6])](NO
3
)
2
7H
2
O, (iii) [Yb(NO
3
)
(H
2
O)
4
](Q[6])](NO
3
)
2
6H
2
O, (iv) [La(H
2
O)
6
(SO
4
)(Q[6])](NO
3
) 12H
2
O, (v)
[Gd(NO
3
)(C
2
H
5
OH)(H
2
O)
2
(H
2
O@Q[6])](NO
3
)
2
5.5H
2
O. Two additional com-
plexes {[Gd(H
2
O)
4
]
2
(Q[6])
3
}Br
6
45H
2
O and {[Ce(H
2
O)
5
]
2
(Q[6])
2
}Br
6
26H
2
O,
obtained employing the corresponding La
3
+
bromide salts, were also isolated (see
later). With the exception of [La(H
2
O)
6
(SO
4
)(Q[6])](NO
3
) 12H
2
O (iv), all of
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