The reactivity of intermolecular complexes cyanoacetylene: acetylene and dicyanoacetylene: acetylene, trapped in solid argon matrixes at 10 K and irradiated with vacuum UV, has been studied. FTIR measurements, together with H-2, N-15, C-13 labeling experiments and with density functional theory (DFT) calculations (B3LYP/aug-cc-pVTZ), pointed to the formation of cyanodiacetylene HC5N (cyanobutadiyne). This synthetic route is potentially important for chemical models of the Titan's atmosphere.