Low‐Temperature Topochemical Synthesis of Cu ₂ Pd ₃ Se ₄ from Layered Rb ₂ Pd ₃ Se ₄ via Molten Salts Ion Exchange

The preparation of kinetically favored inorganic crystals remains a major challenge, as high‐temperature methods often prevent access to metastable phases with unique properties. To address this, post‐synthetic processes that enable the preparation of kinetically favored structures have been developed. In this work, we employ a low‐temperature (200 C) post‐synthetic ion exchange process to transform the parent layered kagome material, RbPdSe, into the nonlayered mineral CuPdSe. This mineral has previously only been synthesized under extreme conditions or was found in nature. Achieving such a structural transformation via ion exchange is unconventional; typical ion exchange reactions mediate transitions between closely related structures. Moreover, the ion exchange procedure developed here does not involve solvents, and the full ion exchange is accomplished at low temperature by the proper choice of a eutectic mixture of salts. Analysis of products synthesized under different conditions show that the CuPdSe decomposition is limited at 200 C when the mixture of CuCl and KCl is used, resulting in a pure‐phase product. The magnetic and electrical characteristics of CuPdSe are presented here for the first time and confirm our density functional theory calculations. Our findings demonstrate that low‐temperature molten salt‐mediated ion exchange may unlock new regions of the solid‐state materials landscape.