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2.3 Simple Coordination Complexes
of Cucurbit[ n , n 7]urils with Metal Ions
A comparison of complexes of Q[ n , n 7]s and Q[5 or 6]s shows that the coor-
dination of Q[ n , n 7]s with metal ions is more difficult than that of Q[5 or 6]
with metal ions. Few of the simple complexes involving with Q[ n , n 7]s have
been reported in Q[ n ]-based coordination chemistry. The larger portal size of Q[ n ,
n 7]s result in an even wider distribution of the carbonyl oxygens, which may be
a reason for the difficulty in the coordination of Q[ n , n 7] with metal ions. The
first crystal structures of Q[7]/metal-based coordination complexes were obtained
by Thuéry. He investigated the influence of perrhenate ions on the structure of lan-
thanide complexes with Q[ n ]s to further probe the properties of Q[ n ]s in perrhenate
encapsulation [ 27 ]. The compound has a very large assembly uniting two differ-
ent Q[7]/Yb 3 + complexes: The first comprises two Q[7] molecules bridged by one
Yb 3 + cation, with two partially included (but not coordinated) [Yb(ReO 4 )(NO 3 )
(H 2 O) 5 ] + cations (Fig. 2.24 a). The second is built from one bidentate Q[7], one
coordinated cation that is disordered over two positions related by a mirror plane,
and one coordinated and included ReO 4
anion (Fig. 2.24 b). However, in the pres-
ence of CsNO 3 or aqueous formic acid, combination of Q[7] with UO 2 (NO 3 ) 2 or
UO 3 can yield simple Q[7]/UO 2 2 + complexes, as shown in Fig. 2.24 c, d, respec-
tively [ 59 ]. In both Q[7]/UO 2 2 + complexes, the UO 2 2 + cation coordinates one por-
tal carbonyl oxygen, and a pair of OH anions link two UO 2 2 + cations.
Even though more Q[8]/metal-based simple complexes have been reported,
only two typical Q[8]/metal-based coordination complexes have been synthesized
Fig. 2.24 X-ray crystal structures of a and b two different Q[7]/Yb 3 + complexes and two
different Q[7]/UO 2 2 + complexes in the presence of c CsNO 3 and d formic acid
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