Coordination Polymers of Cucurbit[n]urils with Metal Ions - Supramolecular Assemblies of Cucurbit[n]urils with Metal Ions - page 70

Fig. 3.30 X-ray crystal structure of two isomeric 1D zigzag polymers constructed of
Q[7]/UO 2 2 + complexes

from the RbCl-Q[7] - Hyq mixture had a stoichiometry of {Rb 2 ( ʼ -OH)(H 2 O) 2 (H
yq@Q[7]) 2 }Cl. The crystal structure shows that a portal of each Q[7] molecule
in the Q[7] pair is covered by a [Rb 2 ( ʼ -OH)(H 2 O) 2 ] unit containing two rubid-
ium cations (2Rb1), and the other portal of each Q[7] molecule in the Q[7] pair
is coordinated to a Rb1 cation belonging to a neighboring rubidium unit. Each of
the Q[7] molecules in the Q[7] pair includes a Hyq guest through the combina-
tion of the cavity bonding of the host Q[7] and the coordination of a Rb1 cation
to a hydroxyl oxygen (O15) of the Hyq guest (Fig. 3.33 a). It should be noted that
O1 and O1A are shared with the other rubidium cation (Rb1A) in the rubidium
unit. In the Q[7] pair, there are additional interactions of the hydroxyl O15-H15A
with the portal carbonyl oxygen O3, as well as interactions of O16-H16 with O12
through hydrogen bonding. The interaction between Rb + and the hydroxyl oxy-
gen (O15) could play an important role in the formation of the Q[7]-Rb + complex
through direct coordination of Q[7] to the rubidium unit [ 55 ].
Remarkably, the crystal structure of the compound shows a 3D infinite frame-
work constructed from the Q[7] pairs through the coordination of the rubidium
unit to the Q[7] molecules (Fig. 3.33 b). From different directions, different lin-
ear channels in the crystal structure of the compound may be seen. For exam-
ple, channels with around 7.45 Å diameter extend along the b axis (Fig. 3.33 c).
However, another set of linear channels of around 10.43 5.2 Å cross-sectional
area (Fig. 3.33 d) can be observed. Close inspection reveals that a network can be