A I SeC 2 H (A I =K, Rb, Cs): Crystalline Compounds with the Elusive − Se‐C≡C‐H Anion

By reaction of alkali metal acetylides, A I C 2 H (A I =K, Rb, Cs), with elemental selenium in liquid ammonia highly crystalline powders of A I SeC 2 H were obtained. The structure analysis based on the resulting synchrotron powder diffraction data revealed that all compounds crystallize in an orthorhombic unit cell (Cmc2 1 , Z =4) exhibiting the elusive − SeC 2 H anion, which is unprecedented in a crystalline compound up to now. Elemental analysis and IR spectroscopic data confirm this finding. Upon heating, A I SeC 2 H compounds release acetylene based on DSC/TGA experiments resulting in powders with the proposed composition A I 2 Se 2 (C 2 ). The resulting powders were indexed with small cubic unit cells, but a reasonable structural model could not be developed up to now. Upon exposure of A I SeC 2 H compounds to water elemental selenium is formed again.