K₂MM‘₃Se₆ (M = Cu, Ag; M‘ = Ga, In), A New Series of Metal Chalcogenides with Chain−Sublayer−Chain Slabs: _∞¹[M‘Se₄]−_∞²[(MSe₄)(M‘Se₄)]−_∞¹[M‘Se₄]

A new series of novel isostructural metal chalcogenides, K2CuIn3Se6 (1), K2CuGa3Se6 (2), and K2AgIn3Se6 (3), were obtained by a reactive flux technique and structurally characterized. Compounds 1, 2, and 3 crystallize in the space group C2/c of the monoclinic system with eight formula units in a cell: a = 11.445(2) Å, b = 11.495(2) Å, c = 21.263(4) Å, β = 97.68(3)°, V = 2772(1) Å3, R1/wR2 = 0.0676/0.1652 for 1; a = 11.031(2) Å, b = 11.050(4) Å, c = 20.808(7) Å, β = 97.71(2)°, V = 2513(1) Å3, R1/wR2 = 0.0301/0.0511 for 2; and a = 11.633(1) Å, b = 11.587(1) Å, c = 21.355(1) Å, β = 98.010(8)°, V = 2850.4(4) Å3, R1/wR2 = 0.0471/0.0732 for 3. These isostructural compounds are characterized by a chain−sublayer−chain slab structure. The sublayer, composed of alternative corner-sharing mixed-metal tetrahedra, is sandwiched by parallel corner-sharing tetrahedral chains. Optical absorption spectra of compounds 1, 2, and 3 reveal the presence of a sharp optical gap of 1.68, 1.72, and 1.64 eV, respectively, suggesting that these materials are semiconductors and suitable for efficient absorption of solar radiation in solar cell applications. IR spectra show no obvious absorption in the range 800−4000 cm-1.本研究通过反应助熔剂法（reactive flux technique）合成了一系列新型同构金属硫族化合物（isostructural metal chalcogenides）：K₂CuIn₃Se₆（1）、K₂CuGa₃Se₆（2）与K₂AgIn₃Se₆（3），并对其晶体结构进行了表征。化合物1、2、3均结晶于单斜晶系（monoclinic system）的空间群（space group）C2/c，晶胞内包含8个化学式单元，其晶胞参数与精修残差因子如下：对于化合物1，a = 11.445(2) Å，b = 11.495(2) Å，c = 21.263(4) Å，β = 97.68(3)°，晶胞体积V = 2772(1) ų，残差因子R1/wR2 = 0.0676/0.1652；对于化合物2，a = 11.031(2) Å，b = 11.050(4) Å，c = 20.808(7) Å，β = 97.71(2)°，V = 2513(1) ų，R1/wR2 = 0.0301/0.0511；对于化合物3，a = 11.633(1) Å，b = 11.587(1) Å，c = 21.355(1) Å，β = 98.010(8)°，V = 2850.4(4) ų，R1/wR2 = 0.0471/0.0732。该系列同构化合物均具有链-亚层-链片层结构（chain−sublayer−chain slab structure）：由交替共顶连接的混金属四面体构成的亚层，被两组平行的共顶四面体链夹在中间。对化合物1、2、3的光吸收谱（optical absorption spectra）测试结果显示，其分别具有1.68 eV、1.72 eV与1.64 eV的尖锐光学带隙（optical gap），表明此类材料为半导体，可应用于太阳能电池中高效吸收太阳辐射。红外光谱（IR spectra）测试表明，该系列化合物在800−4000 cm⁻¹波段内无明显吸收。