NaCu 5 (C 2 ) 3 : The First Alkali Metal Transition Metal Acetylide with a Three‐dimensional Framework Structure

By heating the red residue of the reaction of NaC 2 H and CuI in liquid ammonia at 463 K for 30 min in a dynamic vacuum orange polycrystalline NaCu 5 (C 2 ) 3 is obtained. The crystal structure was solved and refined from X‐ray powder diffraction data (orthorhombic, Pnma, a = 732.80(2) pm, b = 1099.63(4) pm, c = 726.15(2) pm, Z = 4, R B = 0.030). It consists of a three‐dimensional framework of Cu I and C 2 2— ions with small channels running parallel to [100] and [001]. The sodium ions reside at the intersections of these channels. The vibrational spectra of NaCu 5 (C 2 ) 3 show some similarities with the spectra of phenylethynylcopper(I), but they are different to those of Cu 2 C 2 . Therefore NaCu 5 (C 2 ) 3 does probably not represent a crystalline model compound for the unknown structure of amorphous Cu 2 C 2 .