Spectroscopic Properties, Conformation and Structure of Difluorothiophosphoryl Isocyanate in the Gaseous and Solid Phase.

Difluorothiophosphoryl isocyanate, FP(S)NCO was characterized with UV/vis, NMR, IR (gas and Ar-matrix), and Raman (liquid) spectroscopy. Its molecular structure was also established by means of gas electron diffraction (GED) and single crystal X-ray diffraction (XRD) in the gas phase and solid state, respectively. The analysis of the spectroscopic data and molecular structures is complemented by extensive quantum-chemical calculations. Theoretically, the symmetric -conformer is predicted to be the most stable conformation. Rotation about the P-N bond requires about 9 kJ mol and the predicted existence of an -conformer is dependent on the quantum-chemical method used. This orientation of the isocyanate group is the only one found in the gas phase and contained likewise in the crystal. The overall molecular structure is very similar in gas and solid, despite in the solid state the molecules arrange through intramolecular O⋅⋅⋅F contacts into layers, which are further interconnected by S⋅⋅⋅N, S⋅⋅⋅C and C⋅⋅⋅F contacts. Additionally, the photodecomposition of FP(S)NCO to form CO, FP(S)N, and FPNCO is observed in the solid Ar-matrix.