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.

Abstract

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, 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 with exclusively Li counterions such as [Li(en)2.5]4[Ge9] and [Li(en)2]4[E9] (E = Sn and Pb. 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+/[Sn9]4-  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.