AI SeC2 H (AI =K, Rb, Cs): Crystalline Compounds with the Elusive - Se-C≡C-H Anion

By reaction of alkali metal acetylides, A^I C₂ H (A^I =K, Rb, Cs), with elemental selenium in liquid ammonia highly crystalline powders of A^I SeC₂ H were obtained. The structure analysis based on the resulting synchrotron powder diffraction data revealed that all compounds crystallize in an orthorhombic unit cell (Cmc2₁ , Z=4) exhibiting the elusive ^- SeC₂ 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 SeC₂ H compounds release acetylene based on DSC/TGA experiments resulting in powders with the proposed composition A^I ₂ Se₂ (C₂ ). 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 SeC₂ H compounds to water elemental selenium is formed again.