Silver(I) 1,3-Butadiynediide and Two Related Silver(I) Double Salts Containing the C₄^2- Dianion

Ag2C4, the second silver carbide to be fully characterized, has been synthesized as a light-gray powder (contaminated with metallic silver) that is explosive at high temperature (130 °C) and sensitive to mechanical shock, rather like the well-known prototype Ag2C2. In the pair of hydrated double salts Ag2C4·6AgNO3·nH2O (n = 2, 3), the nearly linear, centrosymmetric 1,3-butadiyne-1,4-diyl dianion C42-exhibits an unprecedented μ8-coordination mode, each terminal being capped by four σ-bonded silver(I) atoms with π-interaction to one of them.