Spectral Characterization of Three-Electron Two-Center (3e–2c) Bonds of Gaseous CH₃S∴S(H)CH₃ and (CH₃SH)₂⁺ and Enhancement of the 3e–2c Bond upon Protonation

Abstract

The three-electron two-center (3e-2c) bond plays an important role in structures and electron communication in biological systems involving cationic sulfur compounds. Although the nature of 3e-2c bonds and their theoretical formalism have attracted great interest, direct spectral identifications of 3e-2c-bound molecules are scarce. We observed the infrared spectra of the weakly 3e-2c-bound CHS∴S(H)CH and the strongly 3e-2c-bound (CHSH) in a supersonic jet using infrared (IR) dissociation with vacuum-ultraviolet photoionization and time-of-flight detection. Protonation of CHS∴S(H)CH to form [CH(H)S∴S(H)CH] significantly enhances the 3e-2c bond, characterized by a large red shift of the SH-stretching band with enhanced IR intensity, shortening of the calculated S-S distance from 3.00 to 2.86 Å, and a dissociation energy increased from ∼23 to 162 kJ mol.

Infrared Spectroscopy and Anharmonic Vibrational Analysis of (H2O–Krn)+ (n = 1–3): Hemibond Formation of the Water Radical Cation

“…While the bonding orbital is fully occupied, the antibonding orbital is half occupied, and such an electron configuration results in an effective bond with the bond order of 1/2. The hemibond has attracted much interest in radiation chemistry, especially of sulfur-containing systems, − and recently its roles in biochemistry have also been extensively discussed. − …”

Computational Study of spx(x=1–3)‐Hybridized Be−Be Bonds Stabilized by Amidinate Ligands

“…As shown in the FMOs, the HOMO−1 is a σ‐bonding orbital generally corresponding to Be−Be σ bond, whereas the SOMO (singly occupied molecular orbital) is a σ‐antibonding orbital generally corresponding to Be−Be σ* bond. Consequently, a Be−Be 2c–3e half‐bond is presented, which is similar to the case in Be 2 + . Moreover, the Laplacian of electron density graph (Figure a) exhibits that there is an obvious charge concentration area between two Be atoms, which indicates there is a distinct bonding action in Be−Be.…”

“…The odd‐electron bonds have attracted increasing attention in the field of many optical/electronic materials and catalytic chemistry. They are mainly existent in free‐radical ions and open‐shell species . As to odd‐electron Be−Be chemical bond, such systems are far less and all without exception in the ionic states.…”

Infrared–vacuum ultraviolet spectroscopy of the CH stretching vibrations of jet‐cooled aromatic azine molecules and the anharmonic analysis

“…The experimental setup of IR-VUV spectroscopy combined with time-of-flight mass spectrometry (TOF-MS) for the jet-cooled molecules in the gas phase has been described previously. [18,[25][26][27][28][29] We measured the IR-VUV spectrum of the jet-cooled molecule as an enhanced type (IR + VUV ionization). Here, the VUV laser energy was set below the ionization potential (IP 0 ) of the molecule, and the molecule was ionized when the sum of the energies of IR vibrational excitation (hν IR ) and VUV (hν VUV ) exceeded IP 0 .…”