Cu and Zn Substituted Silicon Clathrates with the Cubic Type‐II Structure: Synthesis and Characterization of Cs ₈8 Na ₁₆16 Cu _3.83.8 Si _132.2132.2 and Cs ₈8 Na ₁₆16 Zn _6.96.9 Si _129.1129.1

摘要

> Studies in the systems Cs–Na–Cu–Si and Cs–Na–Zn–Si yielded the novel clathrates Cs ₈ Na ₁₆ (Cu,Si) ₁₃₆ and Cs ₈ Na ₁₆ (Zn,Si) ₁₃₆ , both with the cubic type‐II structure [space group Fd cssStyle="text-decoration:overline">3 m (no. 227), Pearson symbol cF 160]. The structures of the title compounds were established from single‐crystal X‐ray diffraction methods, confirming the complete ordering of the Cs and Na guest atoms. The framework‐building Si atoms are found to be randomly substituted by Cu atoms on framework site 96 g , exclusively. In the structure of Cs ₈ Na ₁₆ (Zn,Si) ₁₃₆ , the refinements indicate that the Zn and Si atoms co‐occupy two of the three framework sites with notable preference for site 96 g over site 32 e . The corresponding refined compositions and unit cell parameters are as follows: Cs ₈ Na ₁₆ Cu _3.8 Si _132.2(1) [ a = 14.7583(15) ?]; Cs ₈ Na ₁₆ Zn _6.9 Si _129.1(1) [ a = 14.7682(5) ?], respectively. The type‐II clathrates can be obtained only from experiments employing both Na and Cs, whereas work in the ternary Cs‐Cu‐Si, Cs‐Zn‐Si, Na‐Cu‐Si, and Na‐Zn‐Si systems failed to yield any clathrate phases. At the same conditions, exploratory studies in the K‐Zn‐Si and Rb‐Zn‐Si systems provide