Elemental substitution is commonly used in materials chemistry to tune the Fermi energy of a compound or impart Chemical Pressure (CP) to atomic environments. In this Article, we illustrate how such substitution can also allow one to tune the relative orientations of geometrical units within a crystal structure, using the Gd₁₄Ag₅₁ structure type as a demonstration. A key feature of this structure type is the presence of hexagonal columns based on the CaPd_5+x structure type, containing triangles of atoms disordered over two orientations. Synthesis and structure solution of a Zn-substituted variant of this structure, Y₁₄Ag_39.3Zn_12.1, reveal that the incorporation of Zn atoms into these triangles leads to their rotation relative to their surroundings. Distinct triangle orientations are found depending on whether they are Ag₃ or Zn₃ units. A DFT-CP analysis of unsubstituted parent compound Y₁₄Ag₅₁ elucidates these observations. The Ag₃ triangles lie within a large hexagon of Y atoms, with each triangle corner being able to gain close contacts with up to two of these Y atoms depending on the orientation. Obtaining an optimal alignment of the Ag₃ triangles with respect to these interactions, however, is prevented by repulsion from other Ag atoms in the columns derived from the CaPd_5+x type. Instead, the triangles are twisted toward the Y neighbors with larger negative CP features. The replacement of Ag atoms with smaller Zn atoms provides the opportunity to relieve these packing tensions, allowing the triangles to turn to a position that better optimizes their interactions with the surrounding Y atoms. These results point to simple guidelines for identifying, with CP analysis, rigid units within structures that may be manipulated through elemental substitution.

中文翻译：

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Y14Ag39.3Zn12.1 中的化学扭矩：展开 Gd14Ag51 类型的无序三角形


元素取代在材料化学中通常用于调节化合物的费米能或将化学压力 （CP） 赋予原子环境。在本文中，我们以 Gd₁₄Ag₅₁ 结构类型为例，说明了这种替换如何也允许调整晶体结构中几何单位的相对方向。这种结构类型的一个关键特征是存在基于 CaPd_5+x 结构类型的六边形柱，其中包含在两个方向上无序的原子三角形。该结构的 Zn 取代变体 Y₁₄Ag_39.3Zn_12.1 的合成和结构解表明，Zn 原子掺入这些三角形导致它们相对于周围环境的旋转。根据它们是 Ag₃ 还是 Zn₃ 单元，可以找到不同的三角形方向。未取代的母体化合物 Y₁₄Ag₅₁ 的 DFT-CP 分析阐明了这些观察结果。Ag₃ 三角形位于 Y 原子的大六边形内，每个三角形角都能够与最多两个 Y 原子紧密接触，具体取决于方向。然而，获得 Ag₃ 三角形相对于这些相互作用的最佳排列，会受到 CaPd_5+x 型色谱柱中其他 Ag 原子的排斥而无法实现。相反，三角形会向具有较大负 CP 特征的 Y 邻域扭曲。用更小的 Zn 原子取代 Ag 原子提供了缓解这些堆积张力的机会，使三角形能够转向更好地优化它们与周围 Y 原子相互作用的位置。 这些结果为通过 CP 分析识别结构中可以通过元素替换操纵的刚性单元提供了简单的指南。