Kinetically controlled self-assembly of pseudorotaxanes on crystallization

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Crystal Engineering

Background:

• Cyclic host molecules like cyclobis(paraquat-p-phenylene) (CBPQT(4+)) are key components in constructing mechanically interlocked molecules.
• Bis-aryl ethers, such as bis-4-methylphenyl ether (MPE twice) derivatives of 1,5-dioxynaphthalene, offer unique structural motifs for host-guest complexation.

Purpose of the Study:

• To investigate the formation and structural characterization of pseudorotaxanes using CBPQT(4+)) and MPE twice.
• To explore the influence of stoichiometry and crystallization conditions on the resulting supramolecular architectures.
• To identify the stabilizing interactions within the solid-state structures.

Main Methods:

• Stoichiometric mixing of CBPQT(4+)) and MPE twice in specific solvent mixtures (MeCN/CH(2)Cl(2)).
• Crystallization techniques, including direct crystallization and vapor diffusion (using methyl-tert-butyl ether).
• Solid-state structural analysis to determine the nature of the pseudorotaxane assemblies and stabilizing interactions.

Main Results:

• Equimolar mixing and crystallization yielded a [4]pseudorotaxane stabilized by [C-H...F] interactions.
• A 1:3 ratio of CBPQT(4+)) to MPE twice, followed by vapor diffusion, resulted in a crystalline [2]pseudorotaxane.
• The study demonstrates control over pseudorotaxane formation through precise control of component ratios and crystallization methods.

Conclusions:

• The self-assembly of CBPQT(4+)) and MPE twice can lead to distinct pseudorotaxane architectures ([2] and [4] forms).
• Stoichiometry and crystallization conditions are critical parameters for directing the formation of specific supramolecular structures.
• The identified [C-H...F] interactions play a significant role in stabilizing the solid-state [4]pseudorotaxane assembly.