3-electron Bonds Research Articles

Nature of the Three-Electron Bond.

We analyze the properties of 15 3-electron bonds, which include σ-3-electron-bonds, such as dihalide radical anions and di-noble gas radical cations, π-3-electron-bonds as in hydrazine radical cations, and doubly-π-(3e)-bonded species such as O2, FeO+, S2, etc. The primary analytical tool is the breathing-orbital valence-bond (BOVB) method, which enables us to quantify the charge shift resonance energy (RECS) of the three electrons, and the bond dissociation energies (De). BOVB is tested reliable against MRCI calculations. Our findings show that in all 3-electron bonds, none of the VB structures have by themselves any bonding. In fact, in each VB structure, the three electrons maintain Pauli repulsion, while the entire bonding energy arises from resonance due to the charge shift between the two or more constituent VB structures. Hence, 3e-bonds are charge shift bonds (CSBs). The CSB character is probed by calculating the Laplacian (L) of the 3e-bond. Thus, much like the CSBs in electron-pair bonds, such as F2 or the central bond in [1.1.1]propellane, here too L is positive, thus showing the excess kinetic energy of the shared density due to the Pauli repulsion in the 3-electron VB structures. The RECS values for 3-electron bonds are invariably larger than the corresponding bond energies. For the doubly-π-(3e)-bonded species, RECS is very large, exceeding 100 kcal mol-1. As such, it is fitting to conclude that σ- and π-3-electron-bonds find their natural place in the CSB family along with two-electron CSBs, with which they share identical energetic and topological characteristics. Experimental manifestations/tests of 3e-CSBs are proposed.

One-, two-, and three-electron bonding: An “in vitro” theoretical study using noninteger nuclear charges evidences the crucial role of electronegativity in the strength of symmetrical bonds

Fictitious hydrogen atoms H*A of variable nuclear charge 0.5 ≤ ZA ≤ 2 (and thus of variable electronegativity) are used to study the intrinsic dependency of chemical bonding on electronegativity. Dissociation energy and equilibrium distance are reported for symmetrical 1-, 2- and 3-electron H*AH*A systems and 2-electron dissymmetrical H*A-H ones. Dealing with symmetrical systems, the strongest two-electron bonds are found for ZA ≈ 1.2. Oneelectron and three-electron strongest bonds occur respectively with low (ca. 0.7) and high (ca. 1.7) ZA values and can become stronger than the corresponding 2-electron system. Comparison with data on real systems leads to conclude that electronegativity is a prevailing atomic property in the control of the dissociation energy of symmetrical 1-, 2- and 3-electron bonds. A simplified mathematical model at Hartree-Fock or Heitler-London level with a minimal basis set reproduces these trends semi-quantitatively and provides the overall shape of the dissociation curves. Finally some points are qualitatively discussed from MO analysis, which emphasize the dependence of the bonding/antibonding properties on the nucleus charge ZA and their occupancy number. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Stabilization of Oxidized Sulfur and Selenium Centers in Organic Chalcogens by Three-Electron Sulfur-Sulfur, Selenium-Selenium, and Sulfur-Selenium Bonds. A Theoretical Study Using the Semiempirical PM3 Method

Semiempirical computations at the Parimetric Method 3 (PM3) level confirmed an intramolecular stabilization of the radical cations of 1,ω-bis(methylchalcogeno)alkanes by 2-center 3-electron bonds. The formation of bi- and trimolecular associations was also investigated.

A theoretical investigation on the electron-acceptor properties of polar CS bonds of CH3−nFnSH (n = 0–3) thiols and CH3−nFnSCH3−nFn (n = 0–3) sulfides

Abstract The structures and stabilities of fluoro-substituted thiols and sulfides of general formula CH 3− n F n SH and CH 3− n F n SCH 3− n F n ( n = 0–3), have been calculated at the MP2/6-311G ∗∗ and MP2/6-311+ +G ∗∗ levels. The role of F-substitution in molecules and fragments resulting from CS and SH bond cleavage has been studied. In molecules, F-substitution does not bring about important changes of the CS bond lengths, and, accordingly, no important change is observed in the energy of the vertical anion species which remain much less stable than the neutral ground state. The same type of conclusion holds for the homolytic dissociation of neutral molecules (CS and SH bonds), yielding radical moieties, which exhibit only little variation upon F-substitution. When dealing with anion fragments, the situation is more striking. It is noteworthy that the well-documented effect of methyl anions stabilization by halogen substitution is appreciably increased in the new class of compounds of formula CH 3− n F n S. For the latter, the EA rises from 1.47 eV in CH 3 S to 3.08 eV in CF 3 S. On the ground of energy balance between {A 0 + B − ∞ } and {A − + B 0 ∞ } it is proposed that CF 3 SH and CF 3 SCH 3 are good candidates for the adiabatic formation of stable 3-electron bonds.

Qualitative valence bond theory: Speculations concerning the origin of some bond-length variations

Qualitative valence bond rationalizations for the origin of NN,SS and CC bond-length variations are redescribed for N 2O 4, S 2O 4 2− and C 2O 4 2−, and extended to S 2O 5 2−, S 2O 6 2−, C 6H 5SO 2− SO 2C 6H 5 and S 2O 2. Attention is focus on the effect of oxygen lone-pair electron delocalization, and on the resulting long-bond structures and increased-valence structures that are obtained. The NN bond length of 2.237 Å for C 2v symmetry N 2O 2 is contrasted with the CC bond length of 1.525 Å for isoelectronic (HCO) 2. If both bonds were normal single bonds, differences in orbital hybridization would lead to an appreciable weakening of the NN bond relative to the CC bond. A further weakening (and concomitant lengthening) of these bonds occurs when oxygen lone-pair electrons delocalize into the orbitals that form these bonds. It is suggested that the latter type of bond weakening for N 2O 2 can be more than compensated for by the development at large NN internuelear separations of strong NO Pauling ‘3-electron bonds’, which occur in the increased-valence structure. ▪ In contrast, because the CC single bond of CHOCHO is relatively strong, only a slight weakening and lengthening of it through oxygen lone-pair electron delocalization is energetically favourable. A Pople-type SCF molecular orbital procedure, with configuration interaction, is used to help utilize aspects of the photoelectron spectrum for N 2O 2, in order to provide an empirical estimate of the weight for the increased-valence structure.

Qualitative valence-bond representation for electron conduction in copper and related metals

Pauling “3-electron bonds” are used to develop a qualitative valence-bond representation for electron conduction in copper and related metals. For three of the valence-shell electrons on each atom of these metals, the atomic orbital configuration (φ 1) 2(φ 2) 1 is such that the φ 1, and φ 2, orbitals both overlap with the two corresponding orbitals on all adjacent atoms. The valence-bond representation for conduction involves the movement of electrons from either atomic orbitals into 2-centre bonding orbitals or vice versa. Some ab initio valence bond and molecular orbital studies for a model diatomic system with a 6-electron, 4-orbital bonding unit for the valence-shell electrons, provide some insight into differences that exist between the Pauling “3-electron bond” and delocalized molecular orbital wavefunctions for the above class of metals. The Pauling “3-electron bond” representation gives a much smaller importance to closed-shell ionic structures, and therefore the electrons are better correlated when this type of representation is used.

Some aspects of the MO and VB theory for cyclic 6-electron 4-centre bonding units, and VB studies for I 42+

Qualitative MO-CI theory is developed for cyclic 6-electron 4-centre bonding units with D 4h or D 2h symmetry. These bonding units are present in A 4 2+ (A = S, Se or Te), S 2N 2, S 6N 4 2+, [(C 2F 5) 2Se 2] 2 2+ and I 4 2+, each of which has either a π or a σ + π′ “2-electron 4-centre” bond. The delocalized molecular orbitals of the MO-CI wave-function was transformed into localized molecular orbitals, thereby enabling the MO-CI wave-function to be expressed as a linear combination of “covalent” and “ionic” configurations, the more important of which are the covalent configurations. The covalent configurations generate “increased-valence” structures of the general types ( a) and ( b), with Pauling “3-electron bonds” as components, as the primary valence-bond structures for the ground-state. The bonding for the recently reported cation I 4 2+ is described in terms of both “increased-valence” and Lewis structures; semiempirical and ab-initio estimates of valence-bond weights are calculated for this ion. The primary Lewis structures are calculated to be the “long-bond” structures of type ( c). ▪

Pulse radiolysis generation of sulfur radical cations stabilized by neighboring carboxylate and alcohol groups

Described briefly are the results of the pulse radiolytic generation of radical cations derived from dialkyl thioethers. Their molecular structure, including carboxylate and alcohol groups, favors formation of such radicals and increases stability. Pulse radiolysis of the thioethers containing the 10/sup -4/ M endo-carboxylate and the endo-tertiary alcohol groups in N/sub 2/O-saturated aqueous solutions produces previously reported and new transient species. Oxidation of the endo-carboxylate produces a species a 390 nm which exhibits an exponential decay at t/sub 1/2/ = 30, 30, and 50 ..mu..s at pH 3, 7, and 10, respectively. The structure appears to be an adduct possessing a 3-electron bond between sulfur and oxygen. A similar structure appears at pH 4, 420 nm for 30 ..mu..s for the tertiary alcohol group. For the exo-carboxylate, endo- and exo-alcohols, and the exo-tertiary alcohol, the three-electron does not appear. 12 references.

Additions and Corrections - Pauling "3-Electron Bonds", "Increased-Valence", and 6-Electron 4-Center Bonding

Additions and Corrections - Pauling "3-Electron Bonds", "Increased-Valence", and 6-Electron 4-Center Bonding

Pauling "3-electron bonds", "increased-valence", and 6-electron 4-center bonding

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPauling "3-electron bonds", "increased-valence", and 6-electron 4-center bondingRichard D. HarcourtCite this: J. Am. Chem. Soc. 1980, 102, 16, 5195–5201Publication Date (Print):July 1, 1980Publication History Published online1 May 2002Published inissue 1 July 1980https://doi.org/10.1021/ja00536a013RIGHTS & PERMISSIONSArticle Views190Altmetric-Citations48LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (869 KB) Get e-Alerts Get e-Alerts

Free radical oxidation of organic sulphur compounds in aqueous solution

Complexed radical cations are formed as transient products in the one-electron oxidation of organic sulphides by hydroxyl radicals. Intermolecular complexes, (R2S ∴ SR2)+, are characterized by a 3-electron bond between sulphur atoms of two different molecules, absorption maxima around 500 nm and an equilibrium (R2S)2+.⇌ R2S+.+ R2S. In addition, intramolecular complex formation yielding [graphic omitted] is observed in the oxidation of 1,4-di, 1,3-di, and 1,3,5-tri-thiane. In these complexes a 3-electron-through-space-bond between two sulphur atoms of the same molecule is established. Absorption maxima are red shifted to ≥600 nm. Stabilization of an oxidized sulphur atom can also be effected by hetero-atoms other than sulphur. R2S ∴ Br(Cl) are formed in the reaction of either R2S with Br2[graphic omitted](Cl2[graphic omitted]) or the oxidized sulphide with Br–(Cl–). Equilibrium constants for the complexes, spectral and kinetic data on the neutral radicals and radical cations are reported and discussed.