Alkali metal copper acetylides AcuC_2 (A = Na-Cs): synthesis, crystal structures and spectroscopic properties

摘要

By reaction of CuI and A_2C_2 (A = K, Rb, Cs) suspended in liquid ammonia and subsequent heating of the remaining residue in vacuum ternary alkali metal copper acetylides ACuC_2 were accessible. NaCuC_2 could be obtained by decomposing NaCu_5C_6, which was synthesized from NaC_2H and CuI in liquid ammonia. The crystal structures were determined by both X-ray and neutron powder diffraction. In all compounds ~1_infinity (Cu(C_2)_(2/2)~-) chains are the characteristic structural motif. In NaCuC_2 and beta-RbCuC_2 these chains are orientated parallel to the c axis of a tetragonal unit cell (KagC_2 type, P4/mmm, Z = 1), whereas in KCuC_2, alpha-RbCuC_2 and CsCuC_2 these chains are arranged in layers perpendicular to the c axis of a tetragonal unit cell (CsAgC_2 type, P4_2/mmc, Z = 2). These layers are staggered along the c axis by rotating them by 90 deg to each other. The alkali metal ions separate the copper carbon chains. Raman spectroscopic investigations indicate the existence of C-C triple bonds, as the frequencies of the C-C stretching vibration are comparable to those found for acetylene and ternary silver and gold acetylides. In the ~(13)C MAS NMR spectra of KCuC_2, RbCuC_2 and CsCuC_2 the isotropic signals are complicatedly split due to the coupling to the nearby quadrupolar copper nuclei, but the chemical shifts are in the range found for other acetylides with C-C triple bonds.