Molecular capsules based on methyl-substituted cucurbit[5]urils and strontium-capped

Simple Coordination Complexes of Cucurbit[n]urils with Metal Ions

“…Unexpectedly, all (Fig. 2.10c) [14]. The Zn 2+ cation coordinates to the two carbonyl oxygens of a Q [5] portal because of its shorter ionic radius.…”

“…As mentioned previously, we recently reported the new largest member of the Q[n] family, namely tQ [14]. In fact, determination of the structural characteristics of tQ [14] was also first based on the determination of the complex of tQ [14] molecules with the aid of Eu 3+ cations (Fig. 2.26b) [5].…”

“…A Q [5] molecule is included in the cavity of Q [10], and two K + cations, each of which does not fully cover portal of Q [5] molecule, coordinates two portal carbonyl oxygens of the Q [10] molecule. As mentioned previously, we recently reported the new largest member of the Q[n] family, namely tQ [14]. In fact, determination of the structural characteristics of tQ [14] was also first based on the determination of the complex of tQ [14] molecules with the aid of Eu 3+ cations (Fig.…”

“…Although the smaller portal size of Q [5]s inhibits the entry of most organic molecules into the central cavity, and hence reduces the possible range of Q [5]-based host-guest inclusion complexes, it offers a "concentrated" set of five portal carbonyl oxygens so that larger metal ions are able to fully cover the portal and bind to all five oxygens to yield a stable metal-Q [5] complex. Recent studies reveal that Q [5]s have a strong tendency to coordinate with metal ions and form metal-ion-lidded molecular capsules or molecular bowls because Q [5]s have the smaller portal size and more concentrated portal carbony oxygens at portals, which could directly coordinate with metal ions, including alkali, alkaline earth, transition, and lanthanide or uranium [12][13][14][15][16]. Moreover, different Q [5]s, such as the unsubstituted Q [5], and some representative alkyl-substituted Q [5]s, like Me 10 Q [5], dimethylcucurbit [5]uril (DMeQ [5]), 1,2,4-hexamethylcucurbit [5]uril (1,2,4-HMeQ [5]), pentamethylcucurbit [5]uril (PMeQ [5]), pentacyclopentanocuc urbit [5]uril (CyH 5 Q [5]), and so on show no obvious difference in affinity to the metal ions ( Fig.…”

“…Most of them were molecular bowls or molecular capsules. The metal ions included alkali [12,13], alkaline earth [14], transition [15], and lanthanide [16] metal ions. For example, we evaluated the effect of a series of alkaline earth metal ions (Ca 2+ , Sr 2+ , and Ba 2+ ) on their complexes with CyH 5 Q [5] by mixing their chloride salts with CyH 5 Q [5] [20].…”