Selective binding of imidazolium cations in building multi-component layers.

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Organic Chemistry

Background:

• Calixarenes are versatile host molecules with tunable cavities.
• Bis-phosphonium salts and lanthanide ions are known to form complex structures.
• Imidazolium cations are common components in ionic liquids and supramolecular assemblies.

Purpose of the Study:

• To investigate the selective binding of 1-alkyl-3-methylimidazolium (C(n)-mim) cations into calixarene cavities.
• To characterize the structural and dynamic properties of the resulting multi-layered materials.
• To understand the role of lanthanide ions in facilitating complexation.

Main Methods:

• Synthesis of multi-layered materials incorporating C(n)-mim cations, bis-phosphonium cation 2, and sodium p-sulfonatocalix[4]arene (1).
• Structural analysis using X-ray diffraction and NMR spectroscopy (including ROESY NMR).
• Investigation of the effect of varying alkyl chain lengths (ethyl, n-butyl, n-hexyl) on the C(n)-mim cations.

Main Results:

• Selective binding of C(n)-mim cations into the calixarene cavity was achieved, forming 1:1 supermolecules.
• The incorporation of C(n)-mim cations induced significant structural perturbations, notably tilting the calixarene plane.
• Tilt angles increased with longer alkyl chains: 7.2° (ethyl), 28.9° (n-butyl), and 65.5° (n-hexyl).
• Lanthanide ions facilitated complexation but were not incorporated; the calixarene adopted a 5- charge.
• NMR studies indicated rapid exchange of supermolecules on the NMR timescale.

Conclusions:

• The study demonstrates a method for creating multi-layered supramolecular materials with tunable structural properties.
• The length of the alkyl chain on the imidazolium cation plays a critical role in dictating the structural arrangement and dynamics.
• These findings contribute to the understanding of host-guest chemistry and the design of novel functional materials.