NaSeC2H: A Crystalline Compound with Disordered –SeC2H Anions

Abstract

By reaction of NaC2H with elemental selenium (grey or red) in liquid ammonia a crystalline brownish powder of NaSeC2H was obtained. The existence of the new –SeC2H anion – recently discovered in AISeC2H (AI = K, Rb, Cs) – was confirmed by IR spectra showing the expected C≡C, 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. Analysis of the data led to a pyrite‐type structure (Pa3, Z = 4) with a static orientational disorder of the –SeC2H anions over two positions. No phase transition was observed upon cooling to 100 K, where essentially the same structure was obtained with a = 6.989 Å. Upon heating, NaSeC2H releases C2H2 as revealed by thermal analysis (DSC/TGA) resulting in potential Na2Se2C2 crystallizing in a small cubic unit cell with a ≈ 3.899 Å similar to findings on the decomposition of the other AISeC2H compounds.