Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, USA
Inorg Chem. 2012 Jun 4;51(11):6153-63. doi: 10.1021/ic300172k. Epub 2012 May 14.
Black single crystals of A(6)Cu(12)U(2)S(15) (A = K, Rb, Cs) have been synthesized by the reactive flux method. These isostructural compounds crystallize in the cubic space group Ia ̅3d at room temperature. The structure comprises a three-dimensional framework built from US(6) octahedra and CuS(3) trigonal planar units with A cations residing in the cavities. There are no S-S bonds in the structure. To elucidate the oxidation state of U in these compounds, various physical property measurements and characterization methods were carried out. Temperature-dependent electrical resistivity measurement on a single crystal of K(6)Cu(12)U(2)S(15) showed it to be a semiconductor. These three A(6)Cu(12)U(2)S(15) (A = K, Rb, Cs) compounds all exhibit small effective magnetic moments, < 0.58 μ(B)/U and band gaps of about 0.55(2) eV in their optical absorption spectra. From X-ray absorption near edge spectroscopy (XANES), the absorption edge of A(6)Cu(12)U(2)S(15) is very close to that of UO(3). Electronic band structure calculations at the density functional theory (DFT) level indicate a strong degree of covalency between U and S atoms, but theory was not conclusive about the formal oxidation state of U. All experimental data suggest that the A(6)Cu(12)U(2)S(15) family is best described as an intermediate U(5+)/U(6+) sulfide system of (A(+))(6)(Cu(+))(12)(U(5+))(2)(S(2-))(13)(S(-))(2) and (A(+))(6)(Cu(+))(12)(U(6+))(2)(S(2-))(15).
已通过反应熔剂法合成了 A(6)Cu(12)U(2)S(15)（A = K、Rb、Cs）的黑色单晶。这些同构化合物在室温下结晶于立方空间群 Ia ̅3d 中。该结构由 US(6)八面体和 CuS(3)三角平面单元构成的三维骨架组成，A 阳离子位于空腔中。结构中不存在 S-S 键。为了阐明这些化合物中 U 的氧化态，进行了各种物理性质测量和表征方法。对 K(6)Cu(12)U(2)S(15)单晶的温度依赖性电阻测量表明，它是一种半导体。这三种 A(6)Cu(12)U(2)S(15)（A = K、Rb、Cs）化合物在其光吸收光谱中均表现出较小的有效磁矩，<0.58μ(B)/U 和约 0.55(2) eV 的带隙。从 X 射线吸收近边光谱（XANES）来看，A(6)Cu(12)U(2)S(15)的吸收边非常接近 UO(3)。在密度泛函理论（DFT）水平上的电子能带结构计算表明，U 和 S 原子之间具有很强的共价键合程度，但理论并未确定 U 的正式氧化态。所有实验数据表明，A(6)Cu(12)U(2)S(15)系列最好被描述为一种中间 U(5+)/U(6+)硫化物体系，即(A(+))(6)(Cu(+))(12)(U(5+))(2)(S(2-))(13)(S(-))(2)和(A(+))(6)(Cu(+))(12)(U(6+))(2)(S(2-))(15)。
