The "Magic Linker": Highly Effective Gelation from Sterically Awkward Packing.

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Organic Chemistry

Background:

• Low molecular weight gelators (LMWGs) are crucial in materials science for self-assembly.
• Bis(urea) compounds are a well-established class of LMWGs.
• The 4,4'-methylenebis(2,6-diethylphenylene) (4,4'-MDEP) spacer offers unique structural properties.

Purpose of the Study:

• To report the first single crystal structure of a bis(urea) based on the 4,4'-MDEP spacer.
• To investigate the structure-property relationship of 4,4'-MDEP bis(urea)s concerning their gelation behavior.
• To synthesize and evaluate a series of 4,4'-MDEP derivatives as potential gelators.

Main Methods:

• Single crystal X-ray diffraction analysis.
• Synthesis of seven 4,4'-MDEP bis(urea) derivatives.
• Gelation studies in various solvents.

Main Results:

• The first single crystal structure of a 4,4'-MDEP bis(urea) was determined, revealing a conformational isomorph with Z'=8.
• The 2,6-diethylphenylene units exhibited conformational promiscuity, adopting five different conformations.
• Six out of seven synthesized derivatives demonstrated versatile gelation capabilities.
• The nitrophenyl derivative failed to form gels, attributed to intramolecular hydrogen bonding inhibiting the urea tape motif.

Conclusions:

• The 4,4'-MDEP spacer is a highly effective platform for designing low molecular weight gelators.
• Molecular conformation and packing, influenced by the ethyl groups, play a significant role in the gelation ability of these bis(urea)s.
• Intramolecular interactions, such as those in the nitrophenyl derivative, can disrupt the necessary hydrogen-bonding motifs for gel formation.