Polytypism, the ability of materials to form crystal structures with different stacking sequences, occasionally causes materials with the same stoichiometry and similar local structures to have profoundly different properties. Herein, we discover a metastable 13-layer trigonal (13T) polytype of CaGaGe, a layered intermetallic phase comprised of [GaGe]^2– honeycombs separated by Ca²⁺. 13T-CaGaGe is synthesized from arc-melting the elements, and its structure is elucidated via neutron powder diffraction. Air-stable 13T-CaGaGe has one misaligned [GaGe]^2– layer for every 13 and transforms into the more stable 4-layer hexagonal (4H) CaGaGe polytype after annealing at 500 °C. Transition-metal-free 13T-CaGaGe shows remarkable activity in the catalytic hydrogenation of phenylacetylene to styrene and ethylbenzene, much higher than the 4H polytype. This work identifies the first 13-layer polytype for any crystal structure and further establishes the influence of polytypism on catalysis.

中文翻译：

---

幸运数字 13：炔烃氢化催化剂 CaGaGe 的 13 层多型

多型性，即材料形成具有不同堆叠顺序的晶体结构的能力，偶尔会导致具有相同化学计量和相似局部结构的材料具有截然不同的特性。在此，我们发现了一种亚稳态的 13 层三角 (13T) 多型 CaGaGe，一种层状金属间相，由被 Ca ²⁺隔开的 [GaGe] ^2–蜂窝组成。13T-CaGaGe 由元素电弧熔化合成，并通过中子粉末衍射阐明其结构。空气稳定的 13T-CaGaGe 有一个未对准的 [GaGe] ^2–每 13 层，在 500 °C 退火后转变为更稳定的 4 层六边形 (4H) CaGaGe 多型。不含过渡金属的 13T-CaGaGe 在苯乙炔催化氢化成苯乙烯和乙苯方面表现出显着的活性，远高于 4H 多型。这项工作确定了任何晶体结构的第一个 13 层多型，并进一步确定了多型对催化的影响。