Extraction of ternary alloys: Synthesis and crystal structure of[K([2.2.2]crypt)]Cs₇[Sn₉]₂(en) ₃¹

The compound [K([2.2.2]crypt)]Cs₇[Sn₉]₂(en)₃ (1) was synthesized from an alloy of formal composition KCs₂Sn₉ by dissolving in ethylenediamine (en) followed by the addition of [2.2.2]crypt and toluene. 1 crystallizes in the orthorhombic space group Pcca with a = 45.38(2), b = 9.092(4), c = 18.459(8) Å, and Z = 4. The structure consists of Cs₇[Sn₉]₂ layers which contain [Sn₉]^4- anions and Cs⁺ cations. The layers are separated by [K([2.2.2]crypt)]⁺ units. In the intermetallic slab (Cs₇[Sn₉]₂)^- compares the arrange-ment of pairs of symmetry-related [Sn₉]^4- anions with the dimer ([Ge₉]-[Ge₉])^6- in [K([2.2.2]crypt)]₂Cs₄([Ge₉]-[Ge₉]), in which the clusters are linked by a cluster-exo bond. The shortest distance between atoms of such two clusters in 1 is 4.762 Å, e. g. there are no exo Sn-Sn bonds. The [Sn₉]^4- anion has almost perfect C_4v-symmetry.