Structural and Vibrational Properties of the CF₃XXCF₃ (X = O, S, Se, Te) Molecules

Abstract

The structural and vibrational data for the CF 3 XXCF 3 (X = O, S, Se, Te) molecules were compared using DFT quantum chemistry calculations. The experimental vibrational frequencies and their assignments to the different normal modes of vibration could be confirmed. The data was also used to define a scaled quantum mechanics

Trends in the Structural and Vibrational Properties of the Disulfanes S2X2 (X = H, Halogen, CH3, CF3)

“…This observation suggests that the SS bond is larger than expected because of the non‐bonded interaction between the CF 3 groups, which can also be the cause of the relatively large value of the X SS X dihedral angle in CF 3 SSCF 3 (Table 1). In connection with such an observation, it was found that the dihedral angles diminishes clearly when the X atoms are progressively larger in the molecules CF 3 XX CF 3 ( X = O, S, Se, Te) 24. It should be mentioned that the calculated SS lengths do not correlate with the electronegativities as well as the experimental ones.…”

“…As mentioned in the Calculations section, the theoretical Cartesian force constants were transformed to the set of natural (local symmetry) coordinates, which can be found as the Supporting Information associated with the presented work ( X SS X molecules) or with Ref. 24 (CF 3 XX CF 3 molecules). The resulting force constants were scaled in a least‐squares procedure following the method of Pulay et al18 (detailed in the Calculations section), in order to reproduce as well as possible the experimental frequencies.…”

“…The obtained SQM force fields were used for the calculation of a set of internal force constants for each molecule (Table 3). The set of main force constants reported previously for S 2 (CH 3 ) 2 23 and S 2 (CF 3 ) 2 24 are completed now with interaction constants.…”