A Definitive Investigation of the Gas-Phase Two-Center Three-Electron Bond in [H2S-SH2]+, [Me2S-SMe2]+, and [Et2S-SEt2]+: Theory and Experiment

Ding, Ying; Illies, Andreas J.; James, Mary A.; McKee, Michael L.; Peschke, Michael

doi:10.1021/ja00106a048

Cited by 81 publications

(82 citation statements)

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“…The binding energy decreases in the order F ≫ Cl > Br > OH. These binding energies are consistent with those found previously for hemibond complexes involving sulfur [19,22,[24][25][26].…”

Section: Resultssupporting

confidence: 92%

“…The long bond lengths are consistent with previous theoretical results for hemibond complexes involving sulfur [17,19,21,22,[24][25][26]. For example, the S-O distance in the H 2 S⋯OH complex is 2.62 Å, which can be Table 1 Geometric parameters of H 2 S and its complexes with various free radicals obtained at the UCCSD(T)-F12a/AVTZ level and at the MPW1K/AVTZ level (in parentheses)…”

Section: Resultssupporting

confidence: 88%

“…While the angle θ is larger than 90° in the H 2 O⋯X (X = Cl, Br) complexes, the corresponding angle in the H 2 S⋯X complexes is near 90°. Similar right-angled hemibond complexes have been reported before between sulfur-containing molecules and free radicals [17,19,21,22,[24][25][26]. As shown in Fig.…”

Section: Resultssupporting

confidence: 88%

“…Like oxygen-containing molecules, sulfur compounds may also provide lone electron pairs on S, thus allowing the formation of hemibonds with free radicals. In the literature, however, most such complexes investigated before are charged [17,19,21,22,[24][25][26], which complicates the bonding with electrostatic interactions. To further understand the sulfur-containing hemibond complexes, we report here an extensive highlevel ab initio and density functional theory (DFT) study of the complexes formed by H 2 S and several free radicals.…”

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Hemibond complexes between H2S and free radicals (F, Cl, Br, and OH)

Alday

Johnson

et al. 2014

Theor Chem Acc

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as F [4][5][6][7][8] and Cl [9] and found that there often exists a pre-reaction complex between the two reactants. The existence of such complexes has also been reported in other ab initio studies [10][11][12][13]. Interestingly, the F⋯H 2 O complex has been shown to aid the F + H 2 O reaction by guiding the trajectories to the transition state, resulting in a significant enhancement of the reactivity, particularly at low collision energies [14]. More interestingly, it was demonstrated that such complexes are not van der Waals or electrostatic in nature, but due to covalent interactions based on a twocenter three-electron bond [15].Such a two-center three-electron bond was first discussed by Pauling [16]. Due to the fact that one electron is in the antibonding orbital, such a covalent bond is usually quite weak with a relatively long bond length and hence called a hemibond [17]. Hemibond bonding has been found in many branches of chemistry [18], particularly between molecules with lone pairs of electrons and a free radical with an unpaired electron [19-31]. As mentioned above, such hemibond complexes are not only of a fundamental interest, but might also play an important role in molecule-radical reactions. Like oxygen-containing molecules, sulfur compounds may also provide lone electron pairs on S, thus allowing the formation of hemibonds with free radicals. In the literature, however, most such complexes investigated before are charged [17,19,21,22,[24][25][26], which complicates the bonding with electrostatic interactions. To further understand the sulfur-containing hemibond complexes, we report here an extensive highlevel ab initio and density functional theory (DFT) study of the complexes formed by H 2 S and several free radicals. The major aim is to understand the similarities and differences between the H 2 O⋯X and H 2 S⋯X complexes with X = F, Cl, Br, and OH by examining the structural, energetic, and electronic aspects of these interesting systems. AbstractThe interaction of hydrogen sulfide (H 2 S) with F, Cl, Br, and OH is investigated using ab initio methods to identify the two-center three-electron hemibond responsible for their complexation. The binding energies are found to be stronger than those in the analogous water complexes, but follow the same trend of increasing strength: F > Cl > Br > OH. The radicals are located nearly perpendicular to the H 2 S plane forming an angle of about 90°. Analysis of molecular orbitals and natural bond orbitals are carried out to understand the energetics, structures, and bonding characteristics of these hemibonded complexes.

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Section: Resultssupporting

confidence: 92%

Section: Resultssupporting

confidence: 88%

Section: Resultssupporting

confidence: 88%

mentioning

confidence: 99%

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Hemibond complexes between H2S and free radicals (F, Cl, Br, and OH)

Alday

Johnson

et al. 2014

Theor Chem Acc

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“…Se ∴ NH 2 Me COO − + S ∴ NH 2 Me COO − + Quantum chemical calculations of r 2 r* three-electron bonds have revealed, in general, a rather satisfactory picture with respect to their thermodynamic stability and optical transition energies [17][18][19][20]. No such data are, however, yet available for the above S;N and Se;N species and only a few on Se-centered radicals, in general.…”

Section: Met(s∴n) ± Met(se∴n) ±mentioning

confidence: 99%

Theoretical calculations and experimental data on spectral, kinetic and thermodynamic properties of Se∴N and S∴N three-electron-bonded, structurally stabilized σ2σ* radicals

et al. 2009

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A complementary quantum mechanical and experimental study has been undertaken on the reactivity, formation and properties of Se;N and S;N r 2 /r* three-electron-bonded radical species, generated upon one-electron oxidation of selenomethionine, methionine and structurally related compounds. The quantum chemical calculations were based on density functional theory (DFT) hybrid B3LYP and BHandHLYP methods with basis sets ranging from 6-31G(d) to 6-311?G(d,p). Solvent effects, which play an important role concerning structure and energy of ground and excited states, were taken into account as dielectric continuum as well as explicit water molecules. They fully confirm new and previously obtained experimental results concerning the Vis/near-UV absorptions and thermodynamic stability. Special emphasis was put on a comparison between selenium and sulfur. The calculations clearly confirm the higher thermodynamic stability of the Se;N radical species relative to the S;N ones, and also corroborate the observed much higher kinetic stability of the former. Concerning optical absorptions, the calculations predict the Se;N transients to exhibit a blue-shift by about 20 nm relative to the S-based analogues, confirming the few experimental data available so far. The theoretical study includes a comparison of various calculation levels and the influence of the solvent environment, by comparison with vacuum. New experimental data within the scope of this study have been obtained on intramolecularlyformed S;N radical cation moieties, structurally stabilized by a rigid norbornane backbone. The methionine-related species, with an endo-2-amino, exo-2-carboxyl, and endo-6 methylthio substitution, for example, exhibits almost identical optical and kinetic stability properties as the corresponding species from free methionine. Its optical absorption depends on the protonation state of the carboxyl group, with k max at 410 nm for the carboxylate (zwitterionic) form and at 390 nm for the overall cationic form with the protonated carboxyl group. The fast exponential decays with t 1/2 of 490 ns and 2 ls pertain to the decarboxylation of the respective species. A much longer-lived S;N species with t 1/2 [ 500 ls and second order decay kinetics (k max 465 nm) was obtained from an endo-2-cyclohexylamino norbornane analogue which does not carry a carboxyl group. The methionine-based S;N species is not stable anymore in vacuum and in low polarity solvents. This is explained by a decrease in stabilization energy of the 3-e-bond and a faster electron transfer from the carboxylate into the cationic 3-e-center. In conclusion, selenium enhances the thermodynamic and kinetic stability of its radical transients, relative to the sulfur analogues.

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