April 2018

Cyanogen fluoride

With nearly three dozen observed neutral and anionic astromolecules, the cyano group (–CN) is the most commonly observed motif in space. One example of a cyano compound that has not been detected is cyanogen fluoride, FCN, which was sought by Hollis & Ulich in the 1970s. They looked for a single rotational transition of FCN unsuccessfully in four different sources: the star-forming regions W3(OH) and Orion A as well as NGC 2264 and Sgr B2(OH).

Researcher Links
JM Hollis

Cyanogen fluoride or fluorocyanide can be formed in the lab, but it easily polymerizes to cyanuric fluoride (C3N3F3), which has a 6-membered ring structure of alternating C and N atoms with a F atom bonded to each C atom.

As shown in the table below, quantum chemical calculations indicate that the F-CN bond is strong, but it is weaker than the H-F bond. The drive toward equilibrium will thus favor HF (which was found in space in the late 1990s) and may explain the apparent absence of FCN. A possible place where FCN might still be found is a source where methyl fluoride (CH3F) is present, which has a weaker C-F bond than FCN. However, CH3F has not yet been detected.

Bond D0 (kcal/mol)
F–CN 119.3
H–F 133.4
CH3–F 107.4
RCCSD(T)/aug-cc-pVTZ results

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