Cyanoacetylenic complexes as pre-reactional species leading to the HC7N synthesis. Part I: Experimental and theoretical identification of the HC3N:C4H2 complexes

The structures and energies of the cyanoacetylene HC3N and diacetylene C4H2 complexes in argon cryogenic matrix have been investigated using FTIR spectroscopy and ab initio calculations. We establish the structure of two 1:1 complexes. The first one has a linear structure characterized by a hydrogen bond between the nitrogen atom of the cyanoacetylene and one hydrogen of the diacetylene. The second complex, the T-shaped structure, shows an interaction between the hydrogen of cyanoacetylene and the π system of diacetylene. These structures are particularly relevant as they could be pre-reactive states, which can lead to the formation of HC7N.