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 K(5-x)Co(1-x)Sn(9) 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@Sn(9)](5-) clusters that are separated by K(+) ions. The intermetallic compound K(5-x)Co(1-x)Sn(9) 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)[Co(2)Sn(17)]. The novel polyanion [Co(2)Sn(17)](5-) contains two Co-filled Sn(9) clusters that share one vertex. Both compounds were characterized by single-crystal X-ray structure analysis. The diamagnetism of K(5-x)Co(1-x)Sn(9) and the paramagnetism of [K([2.2.2]crypt)](5)[Co(2)Sn(17)] have been confirmed by superconducting quantum interference device (SQUID) and EPR measurements, respectively. Quantum chemical calculations reveal an endohedral Co(1-) atom in an [Sn(9)](4-) nido cluster for [Co@Sn(9)](5-) and confirm the stability of the paramagnetic [Co(2)Sn(17)](5-) unit.