Synthetic Access to Alkali Metal Selenides via Ball Milling

The synthesis of alkali metal selenides often requires harsh reaction conditions and the use of solvents. In this article, we report the synthesis of alkali metal selenides through reactive ball milling under an argon atmosphere. This mechanochemical pathway is solvent‐free and can be performed at room temperature within minutes to hours. The synthesis of several sodium polyselenides (Na 2 Se n , n = 1–6) and alkali metal selenides ( A 2 Se, A = K, Rb, Cs) is investigated and the received products are characterised by powder X‐ray diffraction. We successfully synthesise the sodium selenides Na 2 Se n ( n = 1–4), K 2 Se, Cs 2 Se and a so far unreported polymorph of Rb 2 Se. Additionally, we observe a fierce acceleration of the reaction by PTFE, reducing the reaction time to a few minutes.