The neat ternary solid K(5-x)Co(1-x)Sn9 with endohedral [Co@Sn9]5- cluster units: a precursor for soluble intermetalloid [Co2@Sn17]5- clusters.

A new type of Zintl phase is presented that contains endohedrally filled clusters and that allows for the formation of intermetalloid clusters in solution by a one-step synthesis. The intermetallic compound K5-xCo1-xSn9 was obtained by the reaction of a preformed Co?Sn alloy with potassium and tin at high temperatures. The diamagnetic saltlike ternary phase contains discrete [Co@Sn9]5- clusters that are separated by K+ ions. The intermetallic compound K5-xCo1-xSn9 readily and incongruently dissolves in ethylenediamine and in the presence of 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (2.2.2-crypt), thereby leading to the formation of crystalline [K([2.2.2]crypt)]5[Co2Sn17]. The novel polyanion [Co2Sn17]5- contains two Co-filled Sn9 clusters that share one vertex. Both compounds were characterized by single-crystal X-ray structure analysis. The diamagnetism of K5-xCo1-xSn9 and the paramagnetism of [K([2.2.2]crypt)]5[Co2Sn17] have been confirmed by superconducting quantum interference device (SQUID) and EPR measurements, respectively. Quantum chemical calculations reveal an endohedral Co1- atom in an [Sn9]4- nido cluster for [Co@Sn9]5- and confirm the stability of the paramagnetic [Co2Sn17]5- unit.