Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, USA.
Inorg Chem. 2010 Mar 1;49(5):2568-75. doi: 10.1021/ic902503n.
The compound La(2)U(2)Se(9) was obtained in high yield from the stoichiometric reaction of the elements in an Sb(2)Se(3) flux at 1123 K. The compound, which crystallizes in a new structure type in space group Pmma of the orthorhombic system, has a three-dimensional structure with alternating U/Se and La/Se layers attached via three independent, infinite polyselenide chains. The U atom has a monocapped square antiprismatic coordination of Se atoms, whereas one La atom is bicapped square prismatic and the other La atom is trigonal prismatic. La(2)U(2)Se(9) displays an antiferromagnetic transition at T(N) = 5 K; above 50 K, the paramagnetic behavior can be fit to the Curie-Weiss law, yielding a mu(eff) of 3.10(1) mu(B)/U. The low-temperature specific heat of La(2)U(2)Se(9) exhibits no anomalous behavior near the Neel temperature that might indicate long-range magnetic ordering or a phase transition. X-ray absorption near-edge structure (XANES) spectra have confirmed the assignment of formal oxidation states of +III for lanthanum and +IV for uranium in La(2)U(2)Se(9).
采用元素在 Sb(2)Se(3) 熔剂中于 1123 K 进行化学计量反应的方法，高产率地得到了化合物 La(2)U(2)Se(9)。该化合物在正交晶系 Pmma 空间群中结晶，具有通过三个独立的无限多硒链连接的 U/Se 和 La/Se 交替层的三维结构。U 原子具有由 Se 原子组成的单帽正方形反棱柱配位，而一个 La 原子为双帽正方形棱柱配位，另一个 La 原子为三角棱柱配位。La(2)U(2)Se(9) 在 T(N) = 5 K 处显示出反铁磁转变；在 50 K 以上，顺磁行为可以拟合居里-外斯定律，得到 mu(eff)为 3.10(1) mu(B)/U。La(2)U(2)Se(9) 的低温比热在近奈尔温度处没有异常行为，这可能表明没有长程磁有序或相变。X 射线吸收近边结构（XANES）谱证实了 La(2)U(2)Se(9) 中镧的+III 形式氧化态和铀的+IV 形式氧化态的归属。
