Exploring the Chemical Reaction Space at the Formation of Chalcogenidometalate Superspheres in Ionic Liquids

The synthesis of anionic chalcogenidometalate superspheres can be achieved from [Ge4Se10](4-) salts and SnCl4 in ionic liquids with 1-alkyl-(2,)3-(di)methylimidazolium cations, denoted as (C-n(C-1)C(1)Im)(+) (alkyl = butyl for n=4, hexyl for n=6, octyl for n=8). Their formation is apparently independent from the lengths of the C-n chain, and the presence or absence of a second methyl group at the ionic liquid cation (that are exchanged for alkali metal cations in precursor compounds during the reactions), although this may appear counterintuitive. In contrast, and equally counterintuitive, the ionic liquid anion was found to play a crucial role for both the general observability as well as the crystal yield and quality of the products, although they are not part of the product: a minimum content of chloride is needed, while ionic liquids with [BF4](-) anions alone do not support the product formation/crystallization. The observation suggests a subtle equilibrium of SnCl4 with according halidostannate anions that decreases the reactivity of the tin source. The finding is of particular interest, as chloride anions were shown to have been major impurities of former "chloride-free" ionic liquid charges, which potentially led to irreproducible synthesis protocols in the literature.