The Neat Ternary Solid K 5− x Co 1− x Sn 9 with Endohedral [Co@Sn 9 ] 5− Cluster Units: A Precursor for Soluble Intermetalloid [Co 2 @Sn 17 ] 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 CoSn 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.