Charge‐Transfer Complexes between the Sulfur Molecules SO₂, S₂O, S₃, SONH, and SOCl₂ and the Amine Donors NH₃ and NMe₃ – A Theoretical Study

Abstract

The formation of adducts between the acceptor molecules SO2, S2O, S3, and SOCl2 and the donor molecules ammonia and trimethylamine has been studied by high‐level G3X(MP2) theory, in most cases for the first time. Minimum energy structures with a 1:1 composition and with sulfur–nitrogen bonds have been located for all complexes. The thermodynamic properties, vibrational spectra, and atomic charges of these molecules have been calculated. Of the 10 investigated complexes, only SO2·NMe3 (2) and S2O·NMe3 (4) are predicted to be thermodynamically stable in the gas phase under standard conditions (ΔG°298 < 0). However, all adducts except S3·NH3 (5), SOCl2·NH3 (7), and SOCl2·NMe3 (8) are stable thermodynamically at 77 K. In a polar continuum with a dielectric constant (ϵ) of 40, complexes 2, 4, and S3·NMe3 (6) are stable even at 25 °C. However, if the adducts are formed in the polar continuum from the gaseous components, all adducts except S3·NH3 are formed not only exothermally but also exergonically. Complexes 2, 4, and 8 are the only species known in the solid state so far. The charge transfer from donor to acceptor in the various complexes in the gas phase ranges from 0.08 to 0.39 electrostatic units and correlates inversely with the S–N bond length, which ranges from 198 to 295 pm. In general, the charge transfer weakens the bonds within the acceptor molecule, which therefore may be considered to become activated. The formation of thionyl imide (SONH) from SOCl2 and NH3 is exergonic in the gas phase and the interaction between SONH and NH3 is very weak. In the case of SO2, the 1:2 complexes SO2·2NH3 (1a) and SO2·2NMe3 (2a), which contain two S–N bonds, are unstable with respect to their three‐component molecules both in the gas phase and in a polar medium at 25 °C, but they are stable in the polar phase with respect to the gaseous components.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

“Organic Aqua Regia”—Powerful Liquids for Dissolving Noble Metals

“…These chemical shifts can be attributed to a charge‐transfer interaction between SOCl 2 and py 19. Charge‐transfer complexes between SOCl 2 and amines have been prepared by Schenk and Steudel,20 and studied theoretically by Steudel and Steudel 21. In our case, the sulfur atom in SOCl 2 is an electron acceptor, and the nitrogen atom in pyridine an electron donor.…”

“…In our case, the sulfur atom in SOCl 2 is an electron acceptor, and the nitrogen atom in pyridine an electron donor. Charge transfer, in general, weakens the bonds within the acceptor molecule,21 which accounts for the observed red‐shifts of both the asymmetric and the symmetric Cl‐S‐Cl stretching bands in the Raman spectra of SOCl 2 /py mixtures (see Figure S13 in the Supporting Information). In comparison with pure py and SOCl 2 , we also observe shifts and changes in the intensity of py‐related vibration bands in the FTIR spectra of the SOCl 2 /py mixture (see Figure S14 in the Supporting Information).…”

SO2 Capture Using Porous Organic Cages

“…These bands at 1382 cm -1 and 649 cm -1 are in the range reported for asymmetric stretching and bending for SO2 gas, [53] while the vibrational frequencies at 1226 cm -1 , 1033 cm -1 and 540 cm -1 are associated to the N-S interaction and have been reported for NH3-SO2. [56,57] These results suggest that the adsorption of SO2 occurs mainly at the amino groups, while some free SO2 interacts as a dimer. Additionally, the molecular cage with tertiary amine functionalisation, 6FT-RCC3, showed four vibrational frequencies at 1178 cm -1 , 1083 cm -1 611 cm -1 and 520 cm -1 , which are also related to the formation of an N→SO2 complex, see Fig 4c . 13 C CP MAS NMR experiments (Figure 4 bottom) showed a good correlation with the FT-IR for the solid materials.…”

Amine-Functionalized Covalent Organic Framework for Efficient SO2 Capture with High Reversibility

“…In particular, the ILs functionalized by amine groups have exhibited a very high SO 2 adsorption capacity 14–17 . The chemical interaction between SO 2 and amine groups in the ILs constructs a charge-transfer complex 18, 19 , which forms relatively unstable ionic structure that can reduce the energy requirement for SO 2 desorption 20 .…”