Synthesis of the (Sn$_4$Bi$_4$)$^{2−}$ Anion by Mild Oxidation of (Sn$_2$Bi$_2$)$^{2−}$

Reactions involving Zintl ions are typically carried out in N-based solvents such as liquid ammonia (NH$_{3(l)}$), ethane-1,2-diamine (en), pyridine (py), or acetonitrile (CH$_{3}$CN). We are currently investigating the application of other solvents as alternatives. Herein, we present the synthesis of the (Sn$_4$Bi$_4$)$^{2-}$ anion, obtained as its [K(crypt-222)]$^+$ salt (crypt-222 = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane), from reactions of the binary, pseudo-tetrahedral Zintl anion (Sn$_2$Bi$_2$)$^2$ in the presence of phosphines as oxidation agents in ortho-difluorobenzene (o-DFB). The cluster comprises 38 valence electrons, hence, represents an arachno-type architecture according to Wade-Mingos rules. Micro-X-ray fluorescence (μ-XFS) spectroscopy rationalized the elemental composition of the anion, and quantum chemical studies served to compare the stability of possible structural isomers of the global
minimum structure.