Calixarenes cavity

Based on the above results they have concluded that the ligand groups circularly arranged on the lower rim of the calixarene cavity construct a novel cyclic metal receptor for selective extraction of transition metal cations. Results suggest that the fine tuning in molecular... 

The specific structure of [(H20)5Ni(py)]2+ was observed in the complexes with the second-sphere coordination of calix[4]arene sulfonate.715 There are two different [(H20)5Ni(py)]2+ cations in the complex assembly. In one the hydrophobic pyridine ring is buried in the hydrophobic cavity of the calixarene with the depth of penetration into the calixarene cavity being 4.3 A (Figure 9). The second independent [(H20)5Ni(py)]2+ cation is intercalated into the calixarene bilayer. 

A ferris wheel assembly involving a 1 1 complex of 19 and metallated [18]crown-6 is found in the cationic supermolecule [La(H20)3([ 18]crown-6)] (19+2H) + [48]. The lanthanum ion is coordinated by one calixarene sulfonate group, the [18] crown-6 and three aquo ligands, and the metallated crown sits inside the calixarene cavity. A helical hydrogen bonded chain structure is formed between the cationic assembly, water and chloride ions. The ferris wheel structural motif is also found in Ce3+ complex which simultaneously contains a Russian Doll assembly [44]. 

Calix[4]arenes are characterized by a three-dimensional basket shape, the internal volume being around 10 nm3. Calixarenes exist in different chemical conformations because rotation around the methylene bridge is possible. In calix[4]arene, four conformations are possible cone, partial cone, 1,2-altemate, and 1,3-altemate. These four conformations are in dynamic equilibrium. Conformations can be locked, for instance, by placing a bulkier substituent than the ethyl group on the lower (or narrow) rim, this chain prevents the benzene units from rotating inside the calixarene cavity. 

Figure 3.84 NOE peak intensities upon excitation of the meta-aryl protons of the calixarene cavity...

Figure 1. Calixcrown extractant adopted for CSSX, as complexed with Cs+ ion. Left chemical drawing of the complex. Right a space-filling view of part of a crystal structure of the model complex Cs2Calix[4]arene-bis(benzo-crown-6)(N03)2 3CHCl3 [69] showing the good fit of the Cs+ ion inside the calixarene cavity the crown ether atoms have been removed for clarity.

Very appealing supramolecular structures have been obtained289 with the three-component system consisting of the p-sulfonatocalix[4]arene 143290 (used as its pentasodium salt), pyridine N-oxide and La(N03)3-6H20. If these components are mixed in a 2 2 1 molar ratio 12 calixarene pentaanions, shaped like a truncated pyramid, form spherical supramolecules with the phenolic OH functions inside and the sulfonato groups outside. Coordination of the sulfonato groups and of pyridine N-oxide included in the calixarene cavity to the La3+ stabilizes this assembly. Each sphere is in contact with six other spheres via C-shaped dimers, as shown in Figure 41. 

The complex was characterized by thermogravimetric analysis (TGA) and solid state NMR. Low temperature X-ray crystal structure analysis of the compound indicated the inclusion of CS2 in the calixarene cavity to be highly symmetrically oriented directly on the C4 axis of the host. The CP/MAS experiment showed significant complexation-induced chemical shift (CIS=... 

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