Multifunctional Metal-Organic Frameworks Based on Redox-Active Rhenium Octahedral Clusters.

Area of Science:

• Materials Chemistry
• Inorganic Chemistry
• Nanotechnology

Background:

• Metal-organic frameworks (MOFs) are advanced porous materials with tunable structures and properties.
• Redox-active clusters can impart unique functionalities to MOFs, enabling applications in sensing and catalysis.
• Rhenium-based clusters offer interesting electronic and optical properties for advanced materials development.

Purpose of the Study:

• To synthesize and characterize novel redox-active cluster-based MOFs incorporating rhenium clusters and Gd3+ ions.
• To investigate the gas sorption properties, particularly CO2 uptake and selectivity, of the synthesized MOFs.
• To explore the redox behavior and its impact on the functional properties, including luminescence and sorption.

Main Methods:

• Hydrothermal synthesis of MOFs using [Re6Se8(CN)6]4- clusters, Gd3+ ions, and dicarboxylate linkers (fdc, tdc).
• Characterization using X-ray diffraction, gas sorption analysis (CO2/N2), and UV-Vis spectroscopy.
• Redox titrations and chemical treatments with Br2 and hydrazine to induce and reverse oxidation states.

Main Results:

• Successfully synthesized two novel MOFs, [{Gd(H2O)3}2(L)Re6Se8(CN)6]·nH2O (1, L=fdc; 2, L=tdc), featuring trigonal symmetry and permanent porosity.
• Exhibited high volumetric CO2 uptake and excellent CO2/N2 selectivity at room temperature.
• Demonstrated reversible redox transformations of the rhenium cluster, with oxidation leading to luminescence quenching and altered sorption properties. Complete reversibility achieved using hydrazine.

Conclusions:

• Developed a new class of redox-active, cluster-based MOFs with tunable properties through chemical redox stimuli.
• These MOFs show significant potential as multifunctional materials for selective gas separation.
• The reversible redox behavior suggests applications in chemical sensing and responsive materials.