Synthesis, structure and thermal properties of copper and silver polyynides and acetylides

Polyynes or oligoynes having general formula H-(C equivalent to C)(n)-H with n = 1,2,3,4,., are a class of molecules that has become easily accessible in recent years due to new synthetic approaches. These molecules form copper and silver salts, which have been called, respectively, Cu-polyynides and Ag-polyynides. Here we show the synthesis of these salts and discuss their FT-IR spectra and thermal behaviour, which is studied by Differential Scanning Calorimetry (DSC). These properties are compared to the spectra and thermal behaviour of Cu2C2 and Ag2C2. It is shown that Cu2C2 can be oxidized to Cu-polyynides thereby loosing its original structure and becoming a polymeric coordinative structure. The structural changes make Cu-polyynides no more explosive than the parent Cu2C2. Similarly, Ag-polyynides, which decompose exothermally when heated, are not explosive compared to Ag2C2. The explosive decomposition of Cu2C2 occurs at 127 degrees C ( DSC) whereas Ag2C2 decomposes explosively at 169 degrees C under the same conditions. Conversely, Cu-polyynides, when heated in the DSC, show a broad exothermal peak at about 243 degrees C. Ag-polyynides decompose near 94 degrees C and the release of energy is sufficiently gradual that no explosion is detected.