Coordination Polymers of Cucurbit[n]urils with Metal Ions - Supramolecular Assemblies of Cucurbit[n]urils with Metal Ions - page 55

Fig. 3.16 X-ray crystal structures of a 1D polymer formed through direct coordination of
TMeQ[6] molecules and a Ca 2 + cations; b Rr 2 + cations; and c Ba 2 + cations

polymers in which every two Q[6] molecules are linked by two alkaline earth
metal ions, and the two metal ions are bridged by sharing water molecules or not
bridged.
More recently, our group prepared a series of 1D polymers based on direct
coordination of lanthanides to alkyl-substituted Q[6] in the absence of structure
directing agents or to unsubstituted Q[6] in the presence of structure directing
agents [ 40 - 42 ]. As mentioned, alkyl-substituted Q[ n ]s present different charac-
teristics in coordination with metal ions, suggesting a likely increased electron
density as a consequence of the electrondonating effect of the alkyl substituents.
According to the summary on the coordination of unsubstituted Q[6] with lantha-
nide metal ions and the formation of Q[6]/Ln 3 + -based molecular capsules, molec-
ular bowls, or Q[6]/Ln 3 + pairs are very common, whereas 1D polymers are rare.
Under similar synthetic conditions, hexacyclohexanocucurbit[6]uril (HCyHQ[6])
interacts with lanthanide nitrate in water, generating mainly 1D polymers through
direct coordination of HCyHQ[6] with lanthanide metal ions (Ln = Y, Sm, Eu, Gd,
Tb, Dy, Ho, Er, Yb) [ 40 ]. The structure of the HCyHQ[6]/Sm 3 + complex is given
in Fig. 3.17 as an example. The Sm 3 + cations exhibit octacoordination, with each
Sm 3 + cation (Sm1) coordinated to eight oxygen atoms, viz. four carbonyl oxygen
atoms from two neighboring HCyHQ[6] molecules (O1, O6, O7, and O8) and four
water molecules (O1W, O2W, O3W, and O4W).
Thuéry recently prepared a series of 1D polymers through direct coordination
of Q[6] molecules and lanthanides or uranyl cations in presence of a third spe-
cies. For example, the reaction of lanthanide nitrates with Q[6] under hydrother-
mal conditions in the presence of perrhenic acid can yield two 1D polymers. These