Structural consequences of anionic host-cationic guest interactions in a supramolecular assembly.

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Crystal Engineering

Background:

• Spontaneously assembled supramolecular clusters, denoted as [M(4)L(6)](n-), are complex structures with potential applications in host-guest chemistry.
• Understanding the factors influencing their molecular structure and internal cavity dimensions is crucial for designing functional materials.

Purpose of the Study:

• To investigate the effect of different metal ions and encapsulated guests on the molecular structure of [M(4)L(6)](n-) supramolecular clusters.
• To analyze the interactions between the supramolecular assembly and external cations.
• To quantify the size and packing efficiency of the host-guest complexes.

Main Methods:

• X-ray crystallography was employed to determine the precise molecular structure of the [M(4)L(6)](n-) clusters with various metal ions (Ga(III), Fe(III), Ti(IV)) and guests.
• The rolling probe method was used to model and quantify the solvent-accessible cavity volume.
• Packing coefficients were calculated based on guest and cavity volumes.

Main Results:

• The identity of the metal ions (Ga(III), Fe(III), Ti(IV)) had minimal impact on the overall assembly structure.
• Encapsulated guests (e.g., NEt(4)(+), BnNMe(3)(+), Cp(2)Co(+), Cp*(2)Co(+)) significantly influenced the size and shape of the internal cavity.
• External cations interacted via pi-pi, cation-pi, or CH-pi interactions, with some capable of bridging adjacent assemblies.
• Cavity volumes ranged from 253-434 Å(3), and packing coefficients ranged from 0.47-0.67.

Conclusions:

• The internal cavity of [M(4)L(6)](n-) supramolecular clusters is highly adaptable, primarily influenced by the encapsulated guest molecule.
• The observed packing coefficients suggest efficient utilization of space within the crystal lattice.
• These findings provide insights into the rational design of supramolecular assemblies for specific host-guest applications.