The compounds K0.91U1.79S6 and KU 2Se6, members of the AAn2Q6 actinide family (A = alkali metal or Tl; An = Th or U; Q = S, Se, or Te), have been synthesized from US2, K2S, and S at 1273 K and U, K 2Se, and Se at 1173 K, respectively. KU2Se6 shows Curie-Weiss behavior above 30 K and no magnetic ordering down to 5 K. The value of μeff is 2.95(1) μB/U. Its electronic spectrum shows the peaks characteristic of 5f-5f transitions. It is a semiconductor with an activation energy of 0.27 eV for electrical conduction. Both K0.91U1.79S6 and KU2Se 6 crystallize in space group lmmm of the orthorhombic system and are of the KTh2Se6 structure type. Both contain infinite one-dimensional linear Q-Q chains characteristic of the AAn2Q 6 family. Typical of the known AAn2Q6 compounds, in KU2Se6, there are two alternating Se-Se distances of 2.703(2) and 2.855(2) Å, both much longer than an Se-Se single bond. In contrast, in K0.91U1.79S6, the first sulfide of this family to be characterized structurally, there are alternating normal S22- pairs 2.097(5) Å in length. In K0.91U1.79S6, the formal oxidation state of U is 4+.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry