Vibrational Spectra and Gas Phase Structure of N-Cyanoimidosulfurous Difluoride, NCNSF2

The vibrational spectra, IR (gas) and Raman (liquid) of N-cyanoimidosulfurous difluoride, NCNSF2, were recorded, and the molecular structure was determined by gas electron diffraction. The spectra were assigned by comparing the vibrational frequencies with those in related molecules and with calculated (HF, MP2, B3LYP with 6-31G(d) basis sets) values, and a normal coordinate analysis was performed. The molecule possesses a syn conformation (C⋮N syn with respect to the bisector of the SF2 angle). This has been rationalized by orbital interactions of the electron lone pairs of sulfur and nitrogen with the N−C and S−F bonds, respectively, which are antiperiplanar or anticlinal to these lone pairs (anomeric effects). Quantum chemical calculations with the B3LYP and MP2 methods reproduce the experimental structure reasonably well if large basis sets (6-311G(2d,f)) are used.