Li₂[SeC₂Se]·2NH₃: A Crystalline Ammoniate with a ^-Se-C≡C-Se^- Dianion

Reaction of Li₂C₂ with elemental selenium in a molar ratio of 1:2 in liquid ammonia led to the formation of the ammoniate Li₂[SeC₂Se]·2NH₃. Its crystal structure was solved and refined from high-resolution synchrotron powder diffraction data (P2₁/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 electronic-structure 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 ²Π_u → ³Σ_g^- and ²Π_u → ¹Σ_g⁺ transitions including spin-orbit couplings.