MOFs with 12-Coordinate 5f-Block Metal Centers

Area of Science:

• Materials Science
• Nuclear Chemistry
• Inorganic Chemistry

Background:

• Actinide separation and detection are critical challenges in nuclear science.
• Metal-organic frameworks (MOFs) offer tunable structures for various applications.
• Previous MOF designs have limitations in accommodating heavy actinide elements.

Purpose of the Study:

• To construct a novel MOF platform capable of incorporating multiple tetravalent actinide ions.
• To investigate the structural and electronic properties of actinide-based MOFs (An-MOFs).
• To explore the potential of An-MOFs in distinguishing neighboring actinides and for hard radiation detection.

Main Methods:

• Synthesis of isoreticular actinide metal-organic frameworks (An-MOFs) using tetravalent actinides (Th⁴⁺, U⁴⁺, Np⁴⁺, Pu⁴⁺).
• Characterization of structural properties, including metal coordination environment and porosity.
• Quantum chemical calculations to understand coordination saturation and electronic properties.
• Measurement of autoluminescence and bandgap energy.

Main Results:

• An unprecedented MOF platform accommodating tetravalent actinides (Th⁴⁺, U⁴⁺, Np⁴⁺, Pu⁴⁺) was successfully constructed.
• Periodic trends in the 12-coordinate metal environment and ultramicroporosity were observed.
• Quantum chemical calculations confirmed the feasibility of high coordination numbers in the An-MOF's high-symmetry environment.
• The An-MOFs exhibited autoluminescence (4.16 × 10⁴ counts per second per gram) and wide-bandgap (2.84 eV) semiconducting properties.

Conclusions:

• The developed An-MOF platform demonstrates unique structural and electronic properties, enabling coordination saturation of actinides.
• The framework shows potential for distinguishing between neighboring tetravalent actinides.
• The observed autoluminescence and semiconducting properties suggest applications in hard radiation detection.