Unprecedented Topological Complexity in a Metal-Organic Framework Constructed from Simple Building Units

Area of Science:

• Materials Science
• Crystallography
• Chemistry

Background:

• Metal-organic frameworks (MOFs) are crystalline materials constructed from metal ions or clusters coordinated to organic ligands.
• Bismuth-based MOFs are of interest due to bismuth's unique properties and potential applications.
• Understanding the structural complexity of MOFs is crucial for predicting and optimizing their properties.

Purpose of the Study:

• To synthesize and characterize a novel bismuth-based metal-organic framework (MOF).
• To elucidate the complex crystal structure of the synthesized MOF, CAU-17.
• To investigate the topological complexity of CAU-17 and compare it to known MOF structures.

Main Methods:

• Single-crystal X-ray diffraction was used to determine the crystal structure of CAU-17.
• The structure was analyzed using crystallographic software to identify structural features and connectivity.
• Topological analysis was performed to quantify the complexity of the MOF's network.

Main Results:

• A novel bismuth-based MOF, [Bi(BTC)(H2O)]·2H2O·MeOH (CAU-17), was successfully synthesized.
• CAU-17 exhibits a complex structure with helical bismuth-oxygen rods cross-linked by 1,3,5-benzenetricarboxylate (BTC) ligands.
• The MOF contains five crystallographically independent 1D channels with varying diameters (3.4–9.6 Å) and is further complicated by twinning.
• Topological analysis revealed unprecedented complexity with 54 unique nodes and 135 edges, originating from rod packing and aperiodic helices.

Conclusions:

• CAU-17 represents a highly complex MOF structure, challenging conventional understanding of MOF topology.
• The intricate helical rod arrangement and extensive network complexity in CAU-17 offer new insights into MOF design and formation.
• This discovery highlights the potential for discovering novel and complex structures within the MOF domain.