Na₂C₃O₂ : The First Crystalline Compound with the Elusive ⁻C≡C−COO⁻ Anion

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Krüger, Markus ; Lamann-Glees, Alexandra ; Sebastian, Sean S. ; Siegel, Renée ; Senker, Jürgen ; Hempelmann, Jan ; Dronskowski, Richard ; Ruschewitz, Uwe:
Na₂C₃O₂ : The First Crystalline Compound with the Elusive ⁻C≡C−COO⁻ Anion.
In: Angewandte Chemie International Edition. Bd. 63 (2024) Heft 22 . - e202402978.
ISSN 1521-3773
DOI: https://doi.org/10.1002/anie.202402978

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Abstract

By reaction of sodium electride or NaC2H with the anhydrous sodium salt of propiolic acid, Na(OOC-C equivalent to C-H), in liquid ammonia crystalline powders of Na2C3O2 were obtained. The structure analysis based on synchrotron powder diffraction data revealed that Na2C3O2 crystallizes in a monoclinic unit cell (I2/a, Z=4) exhibiting the elusive Y-shaped -C equivalent to C-COO- anion, which is unprecedented in a crystalline compound up to now. IR/Raman and solid-state NMR spectroscopic investigations with assignments supported by DFT-based ab initio calculations confirm this finding. Reaction with sodium electride led to a higher crystallinity of the product, but additionally a by-product apparently due to decomposition and polymerization of Na2C3O2 was formed. No such by-product was observed in the reaction with NaC2H, which turned out to be a milder metalation route. However, the product of the latter reaction is less crystalline.