Structures and Properties of the Halogenido Stannates(II) [BMIm][Sn$_{3}$3Cl$_{7}$] and [BMIm][Sn$_{4}$Br$_{9}$]

The halogenido stannates(II) [BMIm][Sn$_{3}$Cl$_{7}$] and [BMIm][Sn$_{4}$4Br$_{9}$] are obtained by ionic-liquid-based synthesis with SnX$_{2}$ and [BMIm]X (X=Cl, Br; [BMIm]=1-butyl-3-methylimidazolium) near room temperature (45–50 °C). Both form colorless, moisture-sensitive crystals and exhibit layered anionic networks. [BMIm][Sn$_{3}$3Cl$_{7}$7] contains “horseshoe”-like $_{∞}$$^{1}$(SnCl$_{171}$Cl$_{2/2}$) chains that are linked via [SnCl$_{3}$]− anions to $_{∞}$$^{2}$[Sn$_{3}$Cl$_{7}$]− zigzag-planes. [BMIm][Sn$_{4}$Br$_{9}$] contains a complex $_{∞}$$^{2}$[Sn$_{4}$Br$_{9}$]− network with altogether four different crystallographic Sn$_{2+}$ sites and different coordination. For comparison with these complex halogenido stannates(II), PbCl$_{2}$/PbBr$_{2}$ are reacted with similar conditions, which, however, only results in [BMIm][PbCl$_{3}$] containing $_{∞}$$^{1}$[PbCl$_{3}$]− chains. Beside the crystal structures, the thermal and optical properties are examined and feature certain emission of visible light for all title compounds at room temperature. Whereas the quantum yields of [BMIm][Sn$_{4}$Br$_{9}$9] (3 %) and [BMIm][PbCl$_{3}$] (21 %) are low, [BMIm][Sn$_{3}$Cl$_{7}$] shows surprisingly efficient photoluminescence with a quantum yield of 46 %.