The new quaternary thiosilicate, Li₂PbSiS₄ (dilithium lead silicon tetrasulfide), was prepared in an evacuated fused‐silica tube via high‐temperature, solid‐state synthesis at 800 °C, followed by slow cooling. The crystal structure was solved and refined using single‐crystal X‐ray diffraction data. By strict definition, the title compound crystallizes in the stannite structure type; however, this type of structure can also be described as a compressed chalcopyrite‐like structure. The Li⁺ cation lies on a crystallographic fourfold rotoinversion axis, while the Pb²⁺ and Si⁴⁺ cations reside at the intersection of the fourfold rotoinversion axis with a twofold axis and a mirror plane. The Li⁺ and Si⁴⁺ cations in this structure are tetrahedrally coordinated, while the larger Pb²⁺ cation adopts a distorted eight‐coordinate dodecahedral coordination. These units join together via corner‐ and edge‐sharing to create a dense, three‐dimensional structure. Powder X‐ray diffraction indicates that the title compound is the major phase of the reaction product. Electronic structure calculations, performed using the full potential linearized augmented plane wave method within density functional theory (DFT), indicate that Li₂PbSiS₄ is a semiconductor with an indirect bandgap of 2.22 eV, which compares well with the measured optical bandgap of 2.51 eV. The noncentrosymmetric crystal structure and relatively wide bandgap designate this compound to be of interest for IR nonlinear optics.

中文翻译：

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Li2PbSiS4的合成，晶体结构和电子结构：具有压缩黄铜矿结构的季硫硅酸盐

新的季硫代硅酸盐Li ₂ PbSiS ₄（二硫化铅硅酸铅）是通过在800°C下高温固态合成，然后缓慢冷却的真空石英管中制得的。使用单晶X射线衍射数据解析并精炼了晶体结构。根据严格的定义，标题化合物以锡矿结构类型结晶。但是，这种类型的结构也可以描述为压缩的黄铜矿状结构。Li ⁺阳离子位于晶体四倍旋转转轴上，而Pb ²⁺和Si ⁴⁺阳离子位于四重旋转反转轴与双重轴和镜像平面的交点处。这种结构中的Li ⁺和Si ⁴⁺阳离子是四面体配位的，而较大的Pb ²⁺阳离子则采用扭曲的八坐标十二面体配位。这些单元通过拐角和边缘共享连接在一起，以创建密集的三维结构。粉末X射线衍射表明标题化合物是反应产物的主要相。在密度泛函理论（DFT）中使用全势线性化增强平面波方法进行的电子结构计算表明，Li ₂ PbSiS ₄是具有2.22 eV间接带隙的半导体，与测得的2.51 eV的光学带隙相比具有很好的可比性。非中心对称的晶体结构和相对较宽的带隙使该化合物成为IR非线性光学的关注对象。