Ca₆Cu₂Sn₇: Novel 3D Open Framework with Unusual Sn₄ Tetramers

The new ternary polar intermetallic phase, Ca6Cu2Sn7, has been synthesized by the solid-state reaction of the stoichiometric mixture of the pure elements in welded Ta tubes at high temperature. Its structure was established by single-crystal X-ray diffraction studies. Ca6Cu2Sn7 crystallizes in the monoclinic space group C2/m (No. 12) with cell parameters of a = 14.257(7), b = 4.564(2), and c = 12.376(7) Å, β = 93.979(6)°, V = 803.3(7) Å3, and Z = 2. The structure of Ca6Cu2Sn7 belongs to a new structure type and features a 3D anionic open-framework composed of [Cu2Sn3] layers interconnected by unusual Sn4 tetramers, forming large tunnels along the b axis which are composed of Cu4Sn12 16-membered rings. The calcium atoms are located in these large tunnels. Ca6Cu2Sn7 is metallic and exhibits temperature-independent paramagnetism.新型三元极性金属间化合物相Ca₆Cu₂Sn₇通过固态反应合成：将纯元素按化学计量比混合后封装于焊接钽管中，于高温下进行反应。其晶体结构通过单晶X射线衍射分析得以解析。Ca₆Cu₂Sn₇属于单斜晶系，空间群为C2/m（编号12），晶胞参数为a=14.257(7)、b=4.564(2)、c=12.376(7)埃，β=93.979(6)°，晶胞体积V=803.3(7)埃³，晶胞内化学式单元数Z=2。该结构属于新型结构类型，具有由[Cu₂Sn₃]层通过罕见的Sn₄四聚体相互连接而成的三维阴离子开放骨架，沿b轴方向存在由Cu₄Sn₁₂构成的16元环组成的大型隧道，钙原子即位于此类大型隧道之中。Ca₆Cu₂Sn₇具有金属特性，并表现出温度不依赖性顺磁性。