Synthesis, Crystal Structure, and Liquid Exfoliation of Layered Lanthanide Sulfides KLn₂CuS₆ (Ln = La, Ce, Pr, Nd,...

Among the great amount of known lanthanide nanoparticles, reports devoted to chalcogenide ones are deficient. The properties of such nanoparticles remain almost unknown due to the lack of simple and proper synthetic methods avoiding hydrolysis and allowing preparation of oxygen-free lanthanide nanoparticles. A liquid exfoliation method was used to select the optimum strategy for the preparation of quaternary lanthanide sulfide nanoparticles. Bulk KLn₂CuS₆ (Ln = La-Sm) materials were obtained via a reactive flux method. The crystal structures of three new members of the KLn₂CuS₆ series were determined for Pr, Nd, and Sm as well as for known KLa₂CuS₆. KLn₂CuS₆ (Ln = La, Pr, Nd) compounds crystallize in the monoclinic C2 /c space group, whereas KSm₂CuS₆ crystallizes in the orthorhombic Fddd space group. The analysis of their electronic structures confirms that the main bonding interactions occur within the anionic {Ln₂CuS₆}^- layers. Due to their layered structure, exfoliation of these compounds is possible using ultrasonic treatment in appropriate solvents with the formation of colloidal solutions. Colloidal particles show a plate-like morphology with a lateral size of 100-200 nm and a thickness of 2-10 nm. Highly negative or positive charges found in isopropanol and acetonitrile dispersions, respectively, are associated with high stability and concentration of the dispersions.