Synthesis and spectroscopy of cyanotriacetylene (HC7N) in solid argon

Abstract

UV laser irradiations of cryogenic solid argon matrices doped with a mixture of acetylene and cyanodiacetylene (HC5N) resulted in the formation of a longer carbon-nitrogen chain, cyanotriacetylene (HC7N). The identification of this species was accomplished based on IR vibrational spectroscopy (including the study of isotopically labeled compounds), on electronic luminescence spectroscopy, and on theoretical predictions. Additionally, IR absorption bands recognized as due to HC7N were detected in photolysed Ar matrices doped with a cyanoacetylene/diacetylene mixture; this assignment was confirmed with the mass spectrometry of gases released upon the warm-up of the sample.

Cryogenic Photochemical Synthesis and Electronic Spectroscopy of Cyanotetracetylene

“…1). Stretching modes having similar characteristics also shaped the main vibronic progressions in low-temperature phosphorescence of HC 5 N, 35,66 and HC N. 36,37 These modes also had the highest Raman activity in ground electronic states of the said cyanopolyynes. This is also true for the Raman activity of ν 4 in the ground electronic state of HC 9 N ( Table 2).…”

“…The spacing of 2170 cm -1 is unlikely to be associated with ν 3 . There is a poor match with the predicted ν 3 value of 2201 cm -1 and atomic displacements involved in the vibration ( Table 2 and Table S2) 36 respectively. Furthermore, the yield of (poly)acetylene+cyano(poly)acetylene reactions in rigid matrices is likely decreasing with the increasing size of a cyanopolyacetylenic product.…”

“…It was also seen in Ar, Kr, N 2 , and pH 2 solids containing HC 3 N alone and photolyzed at 193 nm using a laser. 35 Cyanotriacetylene was detected in solid Ar doped with a mixture of either HC 3 N and C 4 H 2 (diacetylene) or HC 5 N and C 2 H 2 , 36 and photolyzed either by excimer laser radiation or an H 2 discharge lamp. The HC 7 N molecule has also been produced by electric discharges in a mixture of HC 3 N and Kr just prior to trapping on a cold window.…”

“…Another might be reactions within existing intermolecular complexes where the reactants are hydrogen bonded in a linear arrangement. Such complexes have been used to explain formation of HC 5 N from matrix-isolated cyanoacetylene:35 The importance of precursors bound in a complex is rather unlikely for syntheses of chains longer than HC 5 N. Experiments leading to formation of HC 7 N showed no IR spectroscopic traces of such complexes, regardless of whether HC 3 N+C 4 H 2 or HC 5 N+C H mixtures were used 36. The same is true for the present experiment using HC 5 N and C 4 H 2 .…”

Low Temperature Synthesis and Phosphorescence of Methylcyanotriacetylene

“…39 In particular, HC 7 N was detected in UV-irradiated (H 2 discharge lamp or 193 nm laser) solid Ar doped with either HC 3 N + C 4 H 2 or HC 5 N + C 2 H 2 mixture. 37 HC 7 N was also produced by electric discharges in a HC 3 N/Kr mixture, prior to the trapping onto a cold substrate. 40 In all these cryogenic approaches, the generated cyanopolyacetylenes were found to emit strong phosphorescence, which proved to be the most sensitive spectroscopic indicator of their presence.…”