1. Department of Chemistry, University of California, Riverside, California 92521, USA
2. Department of Chemistry, University of California, Santa Barbara, California 93106, USA
3. Present address: Department of Chemistry and Biochemistry, California State University, 1250 Bellflower Blvd, Long Beach, California 90840, USA

Correspondence to: Pingyun Feng¹ Email: pingyun.feng@ucr.edu

Natural porous solids such as zeolites are invariably formed with inorganic cations such as Na⁺ and K⁺ (refs 1, 2). However, current research on new porous materials is mainly focused on the use of organic species as either structure-directing or structure-building units; purely inorganic systems have received relatively little attention in exploratory synthetic work^{3, 4, 5, 6, 7, 8, 9}. Here we report the synthesis of a series of three-dimensional sulphides and selenides containing highly mobile alkali metal cations as charge-balancing extra-framework cations. Such crystalline inorganic chalcogenides integrate zeolite-like architecture with high anionic framework polarizability and high concentrations of mobile cations. Such structural features are particularly desirable for the development of fast-ion conductors¹⁰. These materials demonstrate high ionic conductivity (up to 1.8 10^-2 ohm^-1 cm^-1) at room temperature and moderate to high humidity. This synthetic methodology, together with novel structural, physical and chemical properties, may lead to the development of new microporous and open-framework materials with potential applications in areas such as batteries, fuel cells, electrochemical sensors and photocatalysis.