Single crystals of the previously unknown potassium calcium silicate K₂Ca₄Si₈O₂₁ (1) have been grown from a nonstochiometric melt as well as using a KCl flux. The compound is triclinic with the following basic crystallographic data: space group P1̅, a = 6.8052(3) Å, b = 7.1049(3) Å, c = 11.2132(5) Å, α = 96.680(4)°, β = 105.280(4)°, γ = 109.259(4)°, Z = 1, V = 481.28(4) ų. The crystal structure was solved by direct methods based on a single-crystal diffraction data set collected at ambient conditions. From a structural point of view, K₂Ca₄Si₈O₂₁ belongs to the group of single-layer silicates. The layers parallel to (001) are characterized by a complex arrangement of 6-, 8-, 10-, and 12-membered tetrahedral rings. The sheets can be built from the condensation of loop-branched fünfer single chains running parallel to [100], i.e., the crystallochemical formula can be written as K₂Ca₄{lB,5, 1_∞²}[Si₈O₂₁]. Compound 1 is the first example of a loop-branched layer silicate containing secondary (Q²) as well as tertiary (Q³) tetrahedra. Linkage between the layers is provided by calcium and potassium cations, which are distributed among a total of three crystallographically independent nontetrahedral sites. Alternatively, the structure can be described as a heteropolyhedral framework, based on SiO₄ tetrahedra and CaO₆ octahedra. The irregularly coordinated K-cations in turn are incorporated in tunnels of the network running parallel to [110]. The structural investigations have been completed by Raman spectroscopy. The allocation of the bands to certain vibrational species has been aided by density functional theory (DFT) calculations.

中文翻译：

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K ₂ Ca ₄ Si ₈ O _21的合成，晶体结构和振动光谱-一种含Q ²和Q ³单元的不寻常的单层硅酸盐

先前未知的硅酸钾钙K ₂ Ca ₄ Si ₈ O ₂₁（1）的单晶已经从非化学计量的熔体以及使用KCl助熔剂生长而成。该化合物是三斜晶系与以下基本晶体学数据：空间群P 1，一个= 6.8052（3）埃，b = 7.1049（3）埃，c ^ = 11.2132（5）中，α= 96.680（4）°，β= 105.280（4）°，γ= 109.259（4）°，ž = 1，V = 481.28（4）³。通过基于在环境条件下收集的单晶衍射数据集的直接方法来解析晶体结构。从结构的观点来看，K ₂ Ca ₄ Si ₈ O ₂₁属于单层硅酸盐的组。与（001）平行的层的特征在于6元，8元，10元和12元四面体环的复杂排列。片材可从的缩合来构建循环型支化fünfer平行于[100]，即，结晶化学式可以写成为K运行单链₂的Ca ₄ { LB，5，1 _∞ ² } [硅₈ ø ₂₁]。化合物1是包含仲（Q ²）和叔（Q ³）四面体的环状支化层硅酸盐的第一个实例。层之间的连接由钙和钾阳离子提供，钙和钾阳离子分布在总共三个晶体学独立的非四面体位点之间。或者，可以将结构描述为基于SiO ₄四面体和CaO ₆的杂多面体骨架八面体。反过来，不规则配位的K阳离子又被并入平行于[110]的网络隧道中。结构研究已通过拉曼光谱法完成。通过密度泛函理论（DFT）计算来帮助将频带分配给某些振动种类。