Endohedrally filled [Ni@Sn₉]^4- and [Co@Sn₉]^5- Clusters in the Neat Solids Na₁₂Ni_1-xSn₁₇ and K_13-xCo_1-xSn₁₇: Crystal structure and ¹¹⁹Sn solid-state NMR spectroscopy

A systematic approach to the formation of endohedrally filled atom clusters by a high-temperature route instead of the more frequent multistep syntheses in solution is presented. Zintl phases Na₁₂Ni_1-xSn₁₇ and K_13-xCo_1-xSn₁₇, containing endohedrally filled intermetalloid clusters [Ni@Sn₉]^4- or [Co@Sn₉]^5- beside [Sn₄]^4-, are obtained from high-temperature reactions. The arrangement of [Ni@Sn₉]^4- or [Co@Sn₉]^5- and [Sn₄]^4- clusters, which are present in the ratio 1:2, can be regarded as a hierarchical replacement variant of the hexagonal Laves phase MgZn₂ on the Mg and Zn positions, respectively. The alkali-metal positions are considered for the first time in the hierarchical relationship, which leads to a comprehensive topological parallel and a better understanding of the composition of these compounds. The positions of the alkali-metal atoms in the title compounds are related to the known inclusion of hydrogen atoms in the voids of Laves phases. The inclusion of Co atoms in the {Sn₉} cages correlates strongly with the number of K vacancies in K_13-xCo_1-xSn₁₇ and K_5-xCo_1-xSn₉, and consequently, all compounds correspond to diamagnetic valence compounds. Owing to their diamagnetism, K_13-xCo_1-xSn₁₇, and K_5-xCo_1-xSn₉, as well as the d-block metal free binary compounds K₁₂Sn₁₇ and K₄Sn₉, were characterized for the first time by ¹¹⁹Sn solid-state NMR spectroscopy.