The metallic cyanoacetylides CuCCCN, AgCCCN, and AuCCCN have been synthesized in the throat of a pulsed supersonic expansion by reaction of metal vapors, produced by laser ablation, and BrCCCN. Their pure rotational spectra in the (X1Σ+) electronic ground state were observed by Fourier transform microwave spectroscopy in the 2–10 GHz frequency region. Importantly, the rotational spectroscopy constants determined from the analysis of the rotational spectra clearly established the existence of metal–CCCN arrangements for all the mentioned cyanoacetylides. A study of the chemical bonding by means of a topological analysis of the electron density helps to understand the preference for metal–C bonding over metal–N bonding.
