Structures and bonding in K0.91U1.79S6 and KU2Se6.

Area of Science:

• Solid State Chemistry
• Actinide Chemistry
• Materials Science

Background:

• The AAn2Q6 family of actinide compounds exhibits diverse structural and electronic properties.
• Understanding the synthesis and characteristics of new members is crucial for exploring actinide behavior.

Purpose of the Study:

• To synthesize and characterize novel actinide compounds K0.91U1.79S6 and KU2Se6.
• To investigate their structural, electronic, and magnetic properties.

Main Methods:

• High-temperature synthesis from elemental precursors (US2, K2S, S, U, K2Se, Se).
• X-ray crystallography to determine crystal structure and space group (Immm, orthorhombic).
• Magnetic susceptibility measurements (Curie-Weiss behavior) and electronic spectroscopy (5f-5f transitions).
• Electrical conductivity measurements to determine activation energy.

Main Results:

• K0.91U1.79S6 and KU2Se6 were successfully synthesized and crystallized in the KTh2Se6 structure type.
• K0.91U1.79S6 contains S2(2-) pairs with a bond length of 2.097(5) Å, indicating U(IV) oxidation state.
• KU2Se6 exhibits Curie-Weiss behavior above 30 K, is a semiconductor (0.27 eV activation energy), and shows 5f-5f electronic transitions.
• Both compounds feature infinite one-dimensional Q-Q chains.

Conclusions:

• The synthesis of K0.91U1.79S6 expands the known AAn2Q6 family to include sulfides.
• Structural differences in Q-Q chains (S-S vs. Se-Se) influence compound properties.
• KU2Se6 demonstrates semiconducting behavior and characteristic actinide electronic transitions.