A^ISeC₂H (A^I=K, Rb, Cs): Crystalline Compounds with the Elusive ⁻Se‐C≡C‐H Anion

Abstract

By reaction of alkali metal acetylides, AIC2H (AI=K, Rb, Cs), with elemental selenium in liquid ammonia highly crystalline powders of AISeC2H 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 −SeC2H anion, which is unprecedented in a crystalline compound up to now. Elemental analysis and IR spectroscopic data confirm this finding. Upon heating, AISeC2H compounds release acetylene based on DSC/TGA experiments resulting in powders with the proposed composition AI2Se2(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 AISeC2H compounds to water elemental selenium is formed again.

NaSeC2H: A Crystalline Compound with Disordered –SeC2H Anions

“…By reacting NaC 2 H with red or grey selenium in liquid ammonia a brownish precipitate (Figure S1, Supporting Information) was obtained similar to the reactions of the heavier congeners KC 2 H, RbC 2 H, and CsC 2 H . The resulting X‐ray powder diffraction patterns were indexed in cubic unit cells with a ≈ 7.04 Å.…”

“…The resulting X‐ray powder diffraction patterns were indexed in cubic unit cells with a ≈ 7.04 Å. The existence of the newly discovered – SeC 2 H anion was clearly established by IR spectroscopy (see Figure ). However, the elucidation of the crystal structure turned out to be not straight‐forward.…”

“…In our earlier publication we already mentioned that NaSeC 2 H should be accessible under very similar synthetic conditions and its existence was concluded from the signature of the resulting IR spectrum . However, the crystal structure could not be solved from its powder diffraction pattern, which was indexed in a simple cubic unit cell with a ≈ 7.04 Å . It was speculated that the – SeC 2 H anion might be disordered in this compound and low temperature diffraction patterns should be conducted to clarify its crystal structure .…”

“…In our earlier publication we already mentioned that NaSeC 2 H should be accessible under very similar synthetic conditions and its existence was concluded from the signature of the resulting IR spectrum . However, the crystal structure could not be solved from its powder diffraction pattern, which was indexed in a simple cubic unit cell with a ≈ 7.04 Å .…”

“…These compounds were obtained by reacting A I C 2 H with elemental selenium in liquid ammonia resulting in highly crystalline materials. Their crystal structures were elucidated by means of high‐resolution synchrotron powder diffraction patterns ( Cmc 2 1 , Z = 4) and corroborated by IR spectroscopy, elemental analysis, and DSC/TGA investigations . The resulting – SeC 2 H anion was unprecedented in crystalline materials at that time, although it had been postulated as an intermediate in organoselenium reactions, was investigated in gas phase reactions, sometimes as its radical,, or had been of interest in theoretical calculations , …”