Reactivity of Liquid Ammonia Solutions of the Zintl Phase K₁₂Sn₁₇ towards Mesitylcopper(I) and Phosphinegold(I) Chloride

To gain more insight into the reactivity of intermetalloid clusters, the reactivity of the Zintl phase K₁₂Sn₁₇, which contains [Sn₄]^4- and [Sn₉]^4- cluster anions, was investigated. The reaction of K₁₂Sn₁₇ with gold(I) phosphine chloride yielded K₇[(η²-Sn₄)Au(η²-Sn₄)](NH₃)₁₆ (1) and K₁₇[(η²-Sn₄)Au(η²-Sn₄)]₂(NH₂)₃(NH₃)₅₂ (2), which both contain the anion [(Sn₄)Au(Sn₄)]^7- (1 a) that consists of two [Sn₄]^4- tetrahedra linked through a central gold atom. Anion 1 a represents the first binary Au-Sn polyanion. From this reaction, the solvate structure [K([2.2.2]crypt)]₃K[Sn₉](NH₃)₁₈ (3; [2.2.2]crypt=4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) was also obtained. In the analogous reaction of mesitylcopper with K₁₂Sn₁₇ in the presence of [18]crown-6 in liquid ammonia, crystals of the composition [K([18]crown-6)]₂[K([18]crown-6)(MesH)(NH₃)][Cu@Sn₉](thf) (4) were isolated ([18]crown-6=1,4,7,10,13,16-hexaoxacyclooctadiene, MesH=mesitylene, thf=tetrahydrofuran) and featured a [Cu@Sn₉]^3- cluster. A similar reaction with [2.2.2]crypt as a sequestering agent led to the formation of crystals of [K[2.2.2]crypt][MesCuMes] (5). The cocrystallization of mesitylene in 4 and the presence of [MesCuMes]^- (5 a) in 5 provides strong evidence that the migration of a bare Cu atom into an Sn₉ anion takes place through the release of a Mes^- anion from mesitylcopper, which either migrates to another mesitylcopper to form 5 a or is subsequently protonated to give MesH.