Tubular hydrogen-bonded networks sustained by water molecules

Area of Science:

• Supramolecular Chemistry
• Crystal Engineering
• Organic Solid-State Chemistry

Background:

• Functional solids design relies on controlling crystal packing topology via weak intermolecular forces.
• Anticipating the impact of molecular constituents and stereochemistry on cyclic aggregate conformation is crucial for predictable crystal structures.

Purpose of the Study:

• To investigate the influence of steric interactions and substituent flexibility on the solid-state structures of hydroxy acids (+/-)-1.
• To explore the formation of different supramolecular assemblies (tapes, sheets, tubular networks) based on molecular structure and hydration.

Main Methods:

• Synthesis of hydroxy acids with general structure (+/-)-1 and varying substituents.
• X-ray crystallography to determine solid-state structures.
• Analysis of intermolecular interactions, particularly hydrogen bonding and steric effects.

Main Results:

• Compounds with bulky, rigid substituents (except 1b, 1e) formed 1D tapes and 2D sheets via carboxylic acid-to-alcohol hydrogen bonds.
• Compound (+/-)-1n, with flexible substituents, incorporated water to form 3D tubular H-bonding networks with hexagonal channels.
• Smaller substituents failed to form cyclic aggregates, and anhydrous (+/-)-1n formed sheets, highlighting water's role in tubular structures.

Conclusions:

• Steric interactions and substituent flexibility significantly dictate supramolecular assembly in hydroxy acid crystals.
• Water molecules play a critical role in enabling the formation of complex 3D tubular networks.
• The study demonstrates a structure-directing effect of molecular design on the resulting solid-state architecture.