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Abstract

Substituted imidazolium ionic liquids (ILs) were investigated for their reactivity towards Na12Ge17 as a model system containing redox-sensitive Zintl cluster anions. The ILs proved widely inert for imidazolium cations with a 1,2,3-trisubstitution at least by alkyl groups, and for the anion bis(trifluoromethylsulfonyl)azanide (TFSI). A minute conversion of Na12Ge17 observed on long-time contact with such ILs was not caused by dissolution of the salt-like compound, and did thus not provide dissolved Ge clusters. Rather, a cation exchange led to the transfer of Na+ ions into solution. In contrast, by using benzophenone as an oxidizer, heterogeneous redox reactions of Na12Ge17 were initiated, transferring a considerable part of Na+ into solution. At optimized conditions, an X-ray amorphous product NaGe6.25 was obtained, which was thermally convertible to the crystalline type-II clathrate Na24–δGe136 with almost completely Na-filled polyhedral cages, and α-Ge. The presented method thus provides unexpected access to Na24–δGe136 in bulk quantities. © 2021 The Authors. Published by Wiley-VCH GmbH