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An ab initio MO Study of the Gas‐Phase Reactions 2 SF 2 → FS−SF 3 → S=SF 4 − Molecular Structures, Reaction Enthalpies and Activation Energies
Author(s) -
Steudel Yana,
Steudel Ralf,
Wong Ming Wah,
Lentz Dieter
Publication year - 2001
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200109)2001:10<2543::aid-ejic2543>3.0.co;2-6
Subject(s) - chemistry , enthalpy , exothermic reaction , ab initio , endothermic process , ab initio quantum chemistry methods , trigonal bipyramidal molecular geometry , crystallography , isomerization , transition state , standard enthalpy of formation , computational chemistry , crystal structure , molecule , thermodynamics , catalysis , organic chemistry , physics , adsorption
High level ab initio MO calculations at the G3(MP2) level of theory were employed to study the molecular structures of SF 2 , FSSF 3 , and SSF 4 , as well as the dimerization of gaseous SF 2 to FSSF 3 and the isomerization of FSSF 3 to SSF 4 . The dimerization of SF 2 was calculated to be an exothermic process (Δ H ° 298 = −77 kJ·mol −1 ) with an activation enthalpy (Δ H ≠ 298 ) of 65 kJ·mol −1 . The transition state of the dimerization reaction is characterized by a bridging fluorine atom that undergoes a 1,2‐shift, and a weak sulfur‐sulfur single bond. The calculated lowest‐energy structure of FSSF 3 ( 2a ) is in excellent agreement with the experimentally derived structure, with the −SF group in an equatorial position of the distorted pseudo‐trigonal‐bipyramid at the central sulfur atom. A significantly less stable FSSF 3 conformer 2b , 76 kJ·mol −1 higher in energy, has the −SF group in an axial position. Unimolecular rearrangement of FSSF 3 ( 2a ) to the trigonal‐bipyramidal SSF 4 ( 3 ), by a 1,2‐fluorine shift ( TS2 ), is endothermic by 37 kJ·mol −1 and is inhibited by a large activation barrier of 267 kJ·mol −1 . SSF 4 is predicted to be an observable species in the gas phase. Calculated infrared spectra of 2a and 3 are also reported.