Cs2Cd(C2H)2(C2): A Crystalline Acetylide with Bridging C2 Units

Cs2Cd­(C2H)2(C2) was synthesized by heating known Cs2Cd­(C2H)4 either in a dry argon atmosphere at 200 °C or under ammonothermal conditions (130 °C, ∼ 100 bar). The crystal structure of the resulting dark orange-brown microcrystalline material was solved and refined from synchrotron powder diffraction data (Cmcm, Z = 4). Cs2Cd­(C2H)2(C2) is composed of Cd2+ cations tetrahedrally coordinated end-on by four acetylide groups. Two of them are terminating C2H– groups, whereas the other two positions are occupied by bridging C2 2– anions. Thus, a polymeric ∞ 1[Cd­(C2H)2(C2)2/2 2–] chain-like anion results and these chains are separated by Cs+ cations. So obviously Cs2Cd­(C2H)2(C2) is formed from Cs2Cd­(C2H)4 by a condensation reaction of two of its four C2H– groups under the release of one acetylene (C2H2) molecule. This reaction mechanism is supported by DSC/TGA measurements, and the crystal structure of Cs2Cd­(C2H)2(C2) is further supported by IR spectroscopic investigations.