Coordination Polymers of Cucurbit[n]urils with Metal Ions - Supramolecular Assemblies of Cucurbit[n]urils with Metal Ions - page 41

+

Fig. 3.6 X-ray crystal structures of 1D coordination polymers consisting of a CyH 5 Q[5]/Na ;

b CyH 5 Q[5]/Ba 2 + ; and c CyH 5 Q[5]/La 3 +

coordination polymer [ 15 ]. In contrast, Ba 2 + fully covers a portal of CyH 5 Q[5] in
the CyH 5 Q[5]/Ba 2 + -based 1D coordination polymer, and coordinates to two por-
tal carbonyl oxygens of the neighboring CyH 5 Q[5] molecule. This coordination
results in the formation of an 1D polymer constructed from alternating CyH 5 Q[5]
molecules and Ba 2 + cations (Fig. 3.6 b) [ 16 ]. Although the atomic radii of lantha-
nides are generally shorter than those of the alkali or alkaline earth cations, 1D
coordination polymers from alternating CyH 5 Q[5] molecules, and La 3 + cations
(Fig. 3.6 c) may be observed. No portal of the CyH 5 Q[5] molecule is fully covered
with La 3 + , but it offers two portal carbonyl oxygens to coordinate with La 3 + [ 17 ].
Why do the alkyl-substituted SQ[5]s show such different coordination and
supramolecular assemblies from the unsubstituted Q[5]? A comparison of electro-
static potential surface calculations based on density functional theory (B3LYP/3-
21G* basis set) for three typical Q[5]s—Q[5], Me 10 Q[5], and CyP 5 Q[5] (Fig. 3.7 )
shows that the mapped on electron density isosurfaces (0.001 e/au 3 ) for the por-
tal carbonyl oxygens on the three Q[5]s are different, the alkyl-substituted SQ[5]s
are generally more negatively charged as a consequence of the electron donating
effect of the alkyl substituents, we call them as self-structure directing agents,
resulting in more affinity for metal ions, and form novel coordination polymers
and supramolecular assemblies [ 18 - 20 ]. The alkyl-substituted SQ[5]s can not
only form 1D coordination polymers and supramolecular assemblies as shown in
Fig. 3.6 , but can also be linked directly by metal ions to create supramolecular