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.

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.

The recently synthesized acetylide compound KSeCCH containing the main group element selenium within the novel and in crystalline form unprecedented [SeCCH]− anion was successfully investigated in the gas phase by high-resolution velocity-map imaging (VMI) and magnetic-bottle (MB) photoelectron spectroscopy coupled with an electrospray ionization source. Both VMI and MB spectra exhibited identical electron affinities (EA, 2.517 ± 0.002 eV), spin–orbit coupling (SOC) splittings (1492 ± 20 cm–1), and Se–C stretching frequencies (573 ± 20 cm–1) of the corresponding neutral tetra-atomic radical [SeCCH]• with the VMI spectrum possessing six times higher spectral resolution compared with the MB spectrum. These experimental values were well reproduced by calculations at the CCSD­(T) level, in which both the isolated [SeCCH]− anion and the [SeCCH]• radical adopted linear geometries. The simulated spectra based on the calculated Franck–Condon factors, the SOC splitting, and the experimental line width matched well with the measured spectra. Furthermore, comparisons of the EA and SOC splitting values with the previously reported isolobal species [SeCN]• are also made and discussed. The decrease in the EA and SOC splitting of [SeCCH]• is ascribed to the differences in the electronegativities between C and N atoms as well as the electron density on the Se atom in its singly occupied molecular orbital (SOMO).

By reaction of NaC 2 H with elemental selenium (grey or red) in liquid ammonia a crystalline brownish powder of NaSeC 2 H was obtained. The existence of the new-SeC 2 H anion-recently discovered in A I SeC 2 H (A I = K, Rb, Cs)-was confirmed by IR spectra showing the expected CϵC, C-H, and C-Se vibrations. A synchrotron powder diffraction pattern (SNBL, ESRF/Grenoble) was indexed in a cubic unit cell with a = 7.044 Å.

Reaction of Li 2 C 2 with elemental selenium in a molar ratio of 1:2 in liquid ammonia led to the formation of the ammoniate Li 2 [SeC 2 Se]•2NH 3 . Its crystal structure was solved and refined from highresolution synchrotron powder diffraction data (P2 1 /c, Z = 4). It contains the − Se−C�C−Se − anion, unprecedented in a crystalline material, whose existence was corroborated by IR/Raman spectra and electronicstructure theory, showing an almost perfect agreement with calculated spectra. Elaborated magnetic-bottle and velocity-map imaging photoelectron spectroscopic investigations show that the − Se−C�C−Se • radical anion can be transferred to the gas phase, where it was analyzed by NIPE (Negative Ion Photoelectron) and VMI (Velocity-Map Imaging) spectra, which correlate nicely with simulated spectra based on 2 Π u → 3 Σ g − and 2 Π u → 1 Σ g + transitions including spin−orbit couplings.