Infrared spectra of cyanogen halide complexes with hydrogen fluoride in solid argon

Cyanogen chloride was condensed at 12 K with HF in excess argon, producing two 1:1 complexes of the form ClC≡N- -HF (1) and HF- -ClC≡N (2). Increasing the HF concentration produced a 1:2 complex, ClC≡N- -(HF)₂, while increasing the ClC≡N concentration produced a 2:1 complex, ClC≡N- -HF- -ClC≡N. The HF submolecule stretching frequency for the major primary 1:1 complex (1) was observed at 3597 cm^-1, and a single HF librational mode appeared at 602 cm^-1. These fundamentals are comparable to the HF modes for alkyl cyanide complexes. In sharp contrast, the second 1:1 complex (2), which is similar to the HF- -ClF and HF- -Cl₂ complexes, displayed a HF stretching frequency at 3912 cm^-1. Similar results were obtained for cyanogen bromide and cyanogen iodide complexes with hydrogen fluoride and deuterium fluoride. In addition, the photolysis of hydrogen cyanide and fluorine produced the complex FC≡N- -HF with no evidence for a complex analogous to 2. The HF stretching and librational modes for this complex were observed at 3662 and 553 cm^-1, respectively. Similarly, the reaction between cyanogen and HF formed only the N≡CC≡N- -HF complex. The HF modes for this complex were observed at 3757 and 460 cm^-1, which indicate a weaker interaction than found for the cyanogen halides and HF.