Dramatic Changes in Geometry after Ionization:  Experimental and Theoretical Studies on the Electronic Properties of Fluorocarbonyl (Mono-, Di-, and Tri-) Sulfur Compounds

Abstract

In this work, we present a complete study on He I photoelectron spectroscopy (PES) for the fluorocarbonyl mono-, di-, and trisulfur compounds FC(O)SCl, FC(O)SSCH(3), and FC(O)SSSC(O)F. After optimizations of the structure for stable conformers at different levels of theory, a complete theoretical study involving the calculation of the ionization energies using orbital valence Green's functional (OVGF) was performed. Calculations of radical-cationic forms were carried out in order to compare their properties with those of the neutral molecules. The first IP values are 10.7, 9.0, and 10.5 eV for FC(O)SCl, FC(O)SSCH(3), and FC(O)SSSC(O)F, respectively. The groups bonded to the S atom mainly influence the ionizations originating from the sulfur lone pairs. A wide electronic delocalization in the FC(O)S moiety can be deduced from experimental and theoretical results, which leads to a strong energetic stabilization of the n' '(S) (sulfur lone pair pi orbital). Other conclusions relate to effects on the substituents attached to the S atom and the importance of the molecular planarity in the orbital stabilization of the FC(O)S moiety for the neutral molecules. It is worthwhile mentioning that FC(O)SCl retains its planar structure after ionization, but drastic changes occur in the geometry of both FC(O)SSCH(3) and FC(O)SSSC(O)F. The FC(O)SSCH(3) molecule adopts a heavy atom planar structure after ionization. The FC(O)SSS moiety becomes a planar form after the ionization of the FC(O)SSSC(O)F molecule, whereas the second C(O)F group maintains its original conformation with respect to the SSS group.

Synthesis, Structure and Conformational Properties of Fluoroformylchlorodifluoroacetyl Disulfide, FC(O)SSC(O)CF2Cl: Conformational Transferability in –C(O)SSC(O)– Compounds

“…Extensive studies of carbonylsulfenyl compounds with the general formula XC(O)-SY have established the preference for a syn-periplanar conformation around the C-S bond. [20,[30][31][32][33] In the case of disulfides (so that Y corresponds to an -SR group), the preferred mutual orientation of the C=O and S-S bonds is also sp. [12,[14][15][16] It has also been established experimentally that the ap conformation appears as a second stable form that makes appreciable contributions to the vapor at room temperature when X is a fluorine atom, [14,17,34,35] whereas only the sp conformation is adopted by species containing the CF 3 C(O)S moiety.…”

Methyl Fluorocarbonyl Disulfide (FC(O)SSMe): A Theoretical Study on the Structural and Conformational Properties of Its Neutral Ground State and Lowest‐Lying Cationic State

“…This geometric change between the neutral and charged forms may be the reason for the broad band observed in the first band of the photoelectron spectrum of the molecule, corresponding to an electron withdrawn from the lone pair of the S-atom attached to the Me group [18]. The calculated theoretical IP ad , ca.…”

“…These results suggested the preference of the syn form for the d(SSCO) dihedral angle with a characteristic gauche conformation with respect to d(CSSC). The PES was also measured and the bands assigned with the help of the Orbital Valence Green Functional (OVGF) method of calculation [18]. Despite these extensive experimental data, systematic theoretical studies are not yet available for this molecule.…”

“…This diminution in the bond order is easily explained for the first of these modes, because the ionization takes place mainly at the S-atom next to the Me group. The photoelectron spectrum does not allow any assignment for these vibrations [18]. Related to general FC(O)SY-containing compounds, experimental mass spectra of both neutral and charged species of FC(O)SCl and FC(O)SNCO provide evidence that, upon ionization, both the enthalpy difference between the syn and anti conformers and the barrier to internal rotation about the CÀS single bond decrease [37].…”

“…Because of the very poor FrankÀCondon factors for the ionization transition near the threshold displayed by several S-containing molecules, the true IP ad energies could not be observed. The reported value for the vertical ionization potential (IP ver ) for this molecule is 9.0 eV [18]. To compare this vertical ionization energy, a calculation of the energy of the radical cation at the fixed geometry of the neutral ground state was performed.…”