NaSC₂H: A First Crystalline Compound with a ⁻SC₂H Anion, an Isolobal Variant of Ubiquitous ⁻SCN

NaC 2 H is reacted with elemental sulfur in liquid ammonia, yielding crystalline NaSC 2 H as a yellow‐brownish powder. It contains the anion − SC 2 H, an isolobal variant of the well‐known − SCN, thiocyanate. Its existence is confirmed by infrared (IR) and Raman spectroscopy, and its crystal structure is solved and refined using synchrotron powder diffraction data (Swiss Norwegian Beam Line, European Synchrotron/Grenoble). NaSC 2 H crystallizes in a cubic unit cell with a = 6.8507(3) Å (295 K; 100 K: 6.8024(2) Å), analogous to the previously reported NaSeC 2 H. The best Rietveld fit is obtained in a pyrite‐type structure ( Pa , Z = 4) with a static orientation disorder of the − SC 2 H anion across two positions. No phase transition or ordering of the anions is observed down to 100 K. Upon heating or after several days at room temperature, NaSC 2 H releases C 2 H 2 , as shown by thermal analysis (differential scanning calorimetry/thermogravimetric analysis) and gas chromatography. In contrast to NaSeC 2 H, no cubic intermediate with the postulated composition Na 2 S 2 C 2 is formed, but Na 2 S is found in the residue after heating to 200 °C. Possible decomposition reactions for NaSC 2 H are discussed.