The Role of Lithium Ions on the Solubility of K₄E₄ in Ethylenediamine and the Oxidation of the Zintl Anions [E₄]⁴⁻ (E = Ge, Sn, Pb) as well as [Ge₉]⁴⁻

Zintl phases are excellent precursors for nine atom [E₉]⁴⁻ clusters, which are readily accessible by dissolution of A₄E₉ phases (A = Na–Rb; E = Ge–Pb) in ethylenediamine (en). In contrast, the binary alkali-metal tetrel phases of composition A₄E₄ are insoluble in en. Furthermore, Li⁺ cations are rarely investigated as counterions for tetrel element Zintl clusters. We report here that K₄E₄, comprising [E₄]⁴⁻ polyanions (E = Ge, Sn, and Pb), which are insoluble in en, readily dissolves in en in the presence of lithium ions and the four atomic polyanions [E₄]⁴⁻ are oxidized to nine-atom [E₉]⁴⁻ clusters during dissolution. We isolated crystals of [Li(en)_2.5]₄[Ge₉] and [Li(en)₂]₄[E₉] (E = Sn and Pb) with exclusively Li counterions. Furthermore, the alkali-metal ion exchange of K₄Ge₉ with LiCl in en results also in the oxidation of [Ge₉]⁴⁻ to [Ge₉-Ge₉]⁶⁻ dimers which were isolated as partially and fully ion-exchanged salts such as K₂[Li(en)₂]₄[Ge₉-Ge₉] and [Li(en)₂]_6.5[Ge₉-Ge₉], respectively. NMR spectroscopic investigations of solutions of [Sn₉]⁴⁻ that contain variable Li:K ratio reveal contact K⁺/[Sn₉]^4- ion pairs, while Li⁺ ions form solvent-separated ion pairs. The role of Li⁺ ions on the solubility of Zintl phases and Li⁺ assisted oxidation of Zintl ions is highlighted.