Endohedrally Filled [Ni@Sn9]4- and [Co@Sn9]5- Clusters in the Neat Solids Na12Ni1-xSn17 and K13-xCo1-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 Na12Ni1-xSn17 and K13-xCo1-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 K13-xCo1-xSn17 and K5-xCo1-xSn9, and consequently, all compounds correspond to diamagnetic valence compounds. Owing to their diamagnetism, K13-xCo1-xSn17, and K5-xCo1-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. [ABSTRACT FROM AUTHOR]