Kahlenberg Volker
Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52, Innsbruck, Tyrol A-6020, Austria.
Acta Crystallogr B Struct Sci Cryst Eng Mater. 2025 Jun 1;81(Pt 3):325-336. doi: 10.1107/S2052520625002537. Epub 2025 Apr 15.
Single crystals of a previously unknown caesium calcium silicate with the composition CaCa[SiO] have been obtained during a systematic study of the phase relations and compound formation in the system CsO-CaO-SiO. Structure determination was based on a single-crystal diffraction data set recorded at 288 (2) K. The compound crystallizes in the monoclinic space group P2/n and has the following basic crystallographic parameters: a = 7.1670 (6) Å, b = 12.0884 (10) Å, c = 12.4019 (10) Å, β = 90.044 (8)°, V = 1074.47 (15) Å, Z = 2. The crystal structure was solved by direct methods. The sample showed twinning by pseudo-merohedry, which was accounted for in the subsequent least-squares refinements resulting in a residual of R1 = 0.036 for 1962 independent observed reflections and 149 parameters. The crystal structure of CsCa[SiO] belongs to the group of interrupted framework silicates, in which the [SiO] tetrahedra are linked in a three-dimensional network consisting of Q and Q groups in a 1:3 ratio. The linear backbones of the framework can be described as loop-branched dreier single chains. These ribbons are parallel to [100], and the translation period of about 7.2 Å along this axis reflects the periodicity of the chains. By sharing common corners, the condensation of these chains along the [001] direction leads to the formation of layers that are parallel to (010) and contain three- and nine-membered rings of tetrahedra. Alternatively, the crystal structure can be described as a mixed tetrahedral-octahedral framework between [SiO] tetrahedra and [CaO] octahedra containing cavities accommodating the caesium ions coordinated by seven and eight oxygen ligands, respectively. A detailed topological analysis of the mixed framework based on natural tiles is presented. Indeed, the net can be constructed from a total of only two different cages (tiles) having the following face symbols: [4] and [3.4.6.7]. A comparison with related silicates containing [SiO] anions and already classified as well as hitherto unclassified interrupted frameworks is presented. Finally, the thermal expansion tensor has been determined in the temperature interval between 193 K and 288 (2) K.
在对CsO-CaO-SiO体系中的相关系和化合物形成进行系统研究期间，获得了一种此前未知的铯钙硅酸盐单晶，其组成为CaCa[SiO]。结构测定基于在288(2)K记录的单晶衍射数据集。该化合物结晶于单斜空间群P2/n，具有以下基本晶体学参数：a = 7.1670(6) Å，b = 12.0884(10) Å，c = 12.4019(10) Å，β = 90.044(8)°，V = 1074.47(15) Å，Z = 2。晶体结构通过直接法解析。样品显示出假旋转孪晶，在随后的最小二乘精修中对此进行了考虑，对于1962个独立观测反射和149个参数，残余因子R1 = 0.036。CsCa[SiO]的晶体结构属于间断骨架硅酸盐组，其中[SiO]四面体以三维网络相连，该网络由比例为1:3的Q和Q基团组成。骨架的线性主链可描述为环支化的三链单链。这些条带平行于[100]，沿该轴约7.2 Å的平移周期反映了链的周期性。通过共享公共角，这些链沿[001]方向缩合导致形成平行于(010)且包含四面体的三元环和九元环的层。或者，晶体结构可描述为[SiO]四面体和[CaO]八面体之间的混合四面体-八面体骨架，其中包含容纳分别由七个和八个氧配体配位的铯离子的空穴。基于自然瓦片对混合骨架进行了详细的拓扑分析。实际上，网络总共可由仅两种具有以下面符号的不同笼（瓦片）构建：[4]和[3.4.6.7]。与含有[SiO]阴离子且已分类以及迄今未分类的间断骨架的相关硅酸盐进行了比较。最后，在193 K至288(2)K的温度区间内测定了热膨胀张量。
