Nature of the Three-Electron Bond in H₂S∴SH₂⁺

Abstract

We have investigated the model system H2S∴SH2 +, i.e., the sulfur−sulfur bound dimer radical cation of H2S, using both density functional theory (LDA, BP86, PW91) and traditional ab initio theory (up to CCSD(T)). Our purpose is to better understand the nature of the three-electron bond. The S−S bond length is 2.886 Å and the bond enthalpy (for 298.15 K) amounts to −40.7 kcal/mol at the BP86/TZ2P level. The best ab initio estimates for the S−S bond strength (our CCSD(T)/6-311++G(2df,2pd)//MP2(full) and literature values) are some 10 kcal/mol weaker than those from nonlocal DFT. It is shown, using an energy decomposition scheme for open-shell systems, that the sulfur−sulfur bond (ΔE = ΔE 2c-3e + ΔE elst) is nearly 60% provided by the three-electron bond (ΔE 2c-3e) between the unpaired sulfur 3p x electron on H2S+• and the sulfur 3p x lone pair on H2S; electrostatic attraction (ΔE elst) is important, too, with a contribution of somewhat more than 40%. We show furthermore that the three-electron bond (ΔE 2c-3e = ΔE 2c- 1e + ΔE Pauli) can be conceived as and quantitatively analyzed in terms of a one-electron bond (ΔE 2c-1e), arising from the β-electron of the H2S lone pair interacting with the corresponding empty β-spin orbital of H2S+•, opposed by the Pauli repulsion (ΔE Pauli) between the α-electrons of the H2S lone pair and H2S+• SOMO.

Hydrophobicity with atomic resolution: Steady-state and ultrafast X-ray absorption and molecular dynamics studies

“…This interaction has been previously described as a three-electron bond [15], as predicted for Cl 0 and Br 0 [25,26]. Using a Mayer bond order analysis [27], we find that this initial complex has a bond order of 0.32, which is consistent with a three-electron bond [28]. Although the ab initio MD concerns only one trajectory, due to the computational expense, we believe that it is representative of what occurs in Fig.…”

What can we learn from two‐center three‐electron bonding with the topological analysis of ELF?

“…From a theoretical point of view, the most frequently studied species are the rare gas dimer cations [46,47], dihalogen anions [48][49][50], and disulfide ions [51][52][53][54][55], which have long been experimentally identified. In two landmark papers, Clark [3] and Gill and Radom [39] investigated all the model systems of the type H m X І YH + n , attempting to rationalize the existence of 2c-3e bonds.…”

Hypervalent Silicon versus Carbon: Ball‐in‐a‐Box Model

“…[17,18] The analyses were carried out not only in the geometries of the various species that correspond to the D 3h -symmetric 1 a and 2 a (see Figure 2), but also along various deformation modes. First, we analyzed how the bonding changes if one proceeds from the symmetric species along the localization coordinate z, which for 1 and 2 are associated with a convex and concave potential-energy surface (PES), respectively (see Figure 1).…”

“…The trends www.chemeurj.org in the various energy terms were interpreted in the conceptual framework provided by the quantitative molecular orbital (MO) model contained in Kohn-Sham DFT. [18] Qualitative MO analyses of pentacoordination were carried out in the early seventies by Hoffmann and co-workers, [19] who arrived at a bonding mechanism that naturally incorporates the 3-center-4-electron (3c-4e) bond proposed by Pimentel and Rundle [20] to account for the hypervalency of the central atom in species such as F 3 À and XeF 2 . Originally, the 3c-4e bond was formulated in terms of the valence p s atomic orbitals (AOs) of a linear arrangement of three atoms that yields a well-known pattern of three MOs: y 1 , y 2 , and y 3 , shown in Scheme 1.…”