per-Hydroxylated pillar[6]arene: synthesis, X-ray crystal structure, and host-guest complexation

Area of Science:

• Supramolecular Chemistry
• Crystal Engineering
• Organic Chemistry

Background:

• Pillar[6]arenes are macrocyclic compounds with potential host-guest applications.
• Understanding the solid-state arrangement and complexation behavior of functionalized pillararenes is crucial for designing new materials.

Purpose of the Study:

• To synthesize and characterize a per-hydroxylated pillar[6]arene.
• To investigate its solid-state structure and host-guest complexation properties with bispyridinium salts.
• To determine the crystal structure of the resulting host-guest complex.

Main Methods:

• Synthesis of per-hydroxylated pillar[6]arene.
• Single-crystal X-ray diffraction analysis.
• Host-guest complexation studies in solution (spectrophotometry).
• Crystallographic analysis of the complex.

Main Results:

• A per-hydroxylated pillar[6]arene was successfully prepared.
• Solid-state analysis revealed an up-to-down molecular arrangement forming infinite channels.
• Complexation with paraquat in acetone yielded a 1:1 complex with an association constant of 2.2 × 10^2 M⁻¹.
• The crystal structure confirmed the formation of a [2]pseudorotaxane, the first reported for a pillar[6]arene-based system.

Conclusions:

• Per-hydroxylated pillar[6]arene exhibits unique solid-state structural features.
• It effectively forms host-guest complexes, specifically a [2]pseudorotaxane with paraquat.
• This work represents a significant advancement in pillararene supramolecular chemistry and crystal engineering.