Molecular recognition of upper rim functionalized cavitand and its unique dimeric capsule in the solid state

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Host-Guest Chemistry

Background:

• Cavitands are molecular hosts with preorganized cavities.
• 2,2'-Bipyridyl units are known for their coordination and structural properties.
• Selective guest encapsulation is a key challenge in supramolecular chemistry.

Purpose of the Study:

• To investigate the guest-binding capabilities of a novel cavitand (cavitand 1) featuring 2,2'-bipyridyl pillars.
• To elucidate the structural basis for selective guest recognition and complex formation.
• To explore the solid-state assembly and guest interactions of a related cavitand (cavitand 2).

Main Methods:

• Synthesis and characterization of cavitands 1 and 2.
• Guest-binding studies with various small organic molecules.
• Molecular mechanics calculations to model host-guest interactions.
• X-ray crystallography to determine solid-state structures.

Main Results:

• Cavitand 1 selectively encapsulated small guests (e.g., nitromethane, acetonitrile) in a 1:1 host-guest complex.
• Nitroethane and N,N-disubstituted amides were not bound, indicating selectivity.
• Molecular mechanics revealed steric boundaries created by the bipyridyl pillars govern recognition.
• Cavitand 2 formed a chiral capsule via pi-pi stacking, trapping nitromethane through hydrogen bonding.

Conclusions:

• The 2,2'-bipyridyl pillars of cavitand 1 create a defined steric environment for selective guest binding.
• Host-guest complexation is driven by a combination of steric fit and intermolecular interactions.
• Cavitand 2 demonstrates self-assembly into chiral supramolecular structures with specific guest interactions.