Ba2An(S2)2S2 (An = U, Th): syntheses, structures, optical, and electronic properties.

Area of Science:

• Solid-state chemistry
• Inorganic chemistry
• Materials science

Background:

• Actinide chalcogenides are a class of compounds with diverse structures and properties.
• The synthesis and characterization of new actinide-based materials are crucial for understanding their electronic behavior.

Purpose of the Study:

• To synthesize and characterize novel actinide chalcogenides with the formula Ba2An(S2)2S2, where An = U, Th.
• To investigate the crystal structure and electronic properties of these new compounds.

Main Methods:

• High-temperature synthesis reactions involving elements, BaS, and S.
• Single-crystal X-ray diffraction for structural determination.
• Optical measurements (band gap determination) and Density Functional Theory (DFT) calculations.

Main Results:

• Successful synthesis of isostructural Ba2U(S2)2S2 and Ba2Th(S2)2S2 compounds.
• These compounds crystallize in a new tetragonal structure type (P42/nmc) with layered anionic [An(S2)2(S)2(4–)] units.
• The structure features linear An4+ cations bridged by S2– anions and contains unique chalcogen–chalcogen bonds.
• Optical measurements revealed a direct band gap of 2.46(5) eV for Ba2Th(S2)2S2.
• DFT calculations predicted band gaps of 2.2 eV for Ba2Th(S2)2S2 and 1.8 eV for Ba2U(S2)2S2.

Conclusions:

• The novel layered structure and the presence of chalcogen–chalcogen bonds in these actinide chalcogenides are significant findings.
• The calculated and measured band gaps indicate semiconducting properties.
• The study highlights the effectiveness of DFT with the HSE functional for investigating 5f-electron systems.