Potential Applications of Q[n]-Based Coordination Complexes and Polymers - Supramolecular Assemblies of Cucurbit[n]urils with Metal Ions - page 92

Fig. 4.9 a A Lu 3 + -unit; b a basic four-Q[8] building block; c - d 3D frameworks based on the
direct coordination of Lu 3 + cations to Q[8] molecules along different directions [ 13 ]
surrounded by six [CdCl 4 ] 2 − anions through the so-called outer-surface inter-
action of Q[ n ]s. The coordination of Lu 3 + with Q[8] molecules in the presence
of [CdCl 4 ] 2 − anions served as a representative isomorphous complex of the
Ln 3 heavy − Q[8] − [CdCl 4 ] 2 − group, showed an unexpected experimental result. An
Lu 3 + -unit containing four Lu 3 + cations with a 50 % occupancy links four Q[8]
molecules as a basic building block (Fig. 4.9 a, b) and each Lu 3 + -unit links four
Q[8] molecules and forms the basic four-Q[8] building block. In turn, each Q[8]
molecule in the block coordinates with two Lu 3 + -units. Moreover, the extra hydro-
gen bonding of ≡ CH or = CH 2 groups on the back of a Q[8] molecule with portal
carbonyl oxygens of Q[8] exist between every two adjacent Q[8] molecules in the
block (Fig. 4.9 b). Thus, extending the basic building block results in the formation
of a novel 3D framework with various channels, through the direct coordination of
Lu 3 + cations to Q[8] molecules (Fig. 4.9 c, d).
Most interestingly, systems containing the light lanthanides and Q[8] in 6 mol
aqueous HCl have been found to give crystals more rapidly than systems con-
taining the heavy lanthanides. This suggests that the difference could be used to
separate the lighter lanthanides cations from their heavier counterparts. When a
solution of Q[8] in aqueous HCl was added to mixtures of light and heavy lan-
thanides in a 1:1 ratio, for example Ce:Lu, in aqueous HCl solution, stick-like