Bio: Baoan Gong is an academic researcher from Yantai University. The author has contributed to research in topics: Hydrogen bond & Bond order. The author has an hindex of 21, co-authored 53 publications receiving 1218 citations.
TL;DR: Results indicate significant cooperativity between the halogen and hydrogen bonds in these complexes, much greater than that between hydrogen bonds.
Abstract: Ab initio calculations are used to provide information on H(3)N...XY...HF triads (X, Y=F, Cl, Br) each having a halogen bond and a hydrogen bond. The investigated triads include H(3)N...Br(2)-HF, H(3)N...Cl(2)...HF, H(3)N...BrCl...HF, H(3)N...BrF...HF, and H(3)N...ClF...HF. To understand the properties of the systems better, the corresponding dyads are also investigated. Molecular geometries, binding energies, and infrared spectra of monomers, dyads, and triads are studied at the MP2 level of theory with the 6-311++G(d,p) basis set. Because the primary aim of this study is to examine cooperative effects, particular attention is given to parameters such as cooperative energies, many-body interaction energies, and cooperativity factors. The cooperative energy ranges from -1.45 to -4.64 kcal mol(-1), the three-body interaction energy from -2.17 to -6.71 kcal mol(-1), and the cooperativity factor from 1.27 to 4.35. These results indicate significant cooperativity between the halogen and hydrogen bonds in these complexes. This cooperativity is much greater than that between hydrogen bonds. The effect of a halogen bond on a hydrogen bond is more pronounced than that of a hydrogen bond on a halogen bond.
TL;DR: An ab initio study of the complexes formed by hypohalous acids with formaldehyde has been carried out at the MP2/aug-cc-pVTZ computational level, and the energy decomposition analyses indicate that the contribution from the electrostatic interaction energy is larger in the hydrogen-bonding complexes than that in the halogen-bonded complexes.
Abstract: An ab initio study of the complexes formed by hypohalous acids (HOX, X = F, Cl and Br) with formaldehyde has been carried out at the MP2/aug-cc-pVTZ computational level. Two minima complexes are found, one with an H⋯O contact and the other one with an X⋯O contact. The former is more stable than the latter, and the strength difference between them decreases as the size of the X atom increases. The associated HO and XO bonds undergo a bond lengthening and red shift, whereas a blue shift was observed in the bond of the hypohalous acid not involved in the interaction. The interaction strength and properties in both complexes are analyzed with atoms in molecules (AIM) and natural bond orbital (NBO) theories. The energy decomposition analyses indicate that the contribution from the electrostatic interaction energy is larger in the hydrogen-bonded complexes than that in the halogen-bonded complexes.
TL;DR: This paper suggested some measures for enhancing the strength of the halogen bond relative to the hydrogen bond in the H(2)CS-HOX (X = F, Cl, and Br) system by means of quantum chemical calculations.
Abstract: The properties and applications of halogen bonds are dependent greatly on their strength. In this paper, we suggested some measures for enhancing the strength of the halogen bond relative to the hydrogen bond in the H2CS–HOX (X = F, Cl, and Br) system by means of quantum chemical calculations. It has been shown that with comparison to H2CO, the S electron donor in H2CS results in a smaller difference in strength for the Cl halogen bond and the corresponding hydrogen bond, and the Br halogen bond is even stronger than the hydrogen bond. The Li atom in LiHCS and methyl group in MeHCS cause an increase in the strength of halogen bonding and hydrogen bonding, but the former makes the halogen bond stronger and the latter makes the hydrogen bond stronger. In solvents, the halogen bond in the Br system is strong enough to compete with the hydrogen bond. The interaction nature and properties in these complexes have been analyzed with the natural bond orbital theory.
TL;DR: In the present paper, a new type of lithium bonding complex HMgHLiX (X = H, OH, F, CCH, CN, and NC) has been predicted and characterized and the Li-X harmonic vibrational stretching frequency is blueshifted and redshifted in the HMg HLiX complexes.
Abstract: In the present paper, a new type of lithium bonding complex HMgH⋯LiX (X = H, OH, F, CCH, CN, and NC) has been predicted and characterized. Their geometries (C∞v) with all real harmonic vibrational frequencies were obtained using the second-order Moller–Plesset perturbation theory (MP2) with 6-311++G(d,p) basis set. For each HMgH⋯LiX complex, a lithium bond is formed between the negatively charged H atom of an HMgH molecule and the positively charged Li atom of an LiX molecule. Due to the formation of the complexes, the Mg–H and Li–H bonds are elongated. Interestingly, the Li–X harmonic vibrational stretching frequency is blueshifted in the HMgH⋯LiX (Y = CCH, CN, and NC) complexes and redshifted in the HMgH⋯LiX (X = H, OH, and F) complexes. The binding energy of this type of lithium bond ranges from 12.18 to 15.96 kcal mol−1, depending on the chemical environment of the lithium. The nature of lithium–hydride lithium bond has also been analyzed with natural bond orbital (NBO) and atoms in molecules (AIM).
TL;DR: In this article, an unconventional halogen bond has been proved to exist in H2C-BrH complex and the halogen energy of H2c-BrCN complex is calculated at four levels of theory [MP2, MP4, CCSD, and CCSd(T)].
Abstract: An unconventional halogen bond has been proved to exist in H2C–BrH complex. The halogen bond energy of H2C–BrH complex is calculated at four levels of theory [MP2, MP4, CCSD, and CCSD(T)]. The result shows that the carbene is a better electron donor. The substitution effect is prominent in this interaction. For example, the interaction energy in H2C–BrCN complex is increased by more than 300% relative to H2C–BrH complex. The analyses of NBO, AIM, and energy components were used to unveil the nature of the interaction. The results show that this novel halogen bond has similar characteristics to hydrogen bonds.
TL;DR: A σ-hole bond is a noncovalent interaction between a covalently-bonded atom of Groups IV-VII and a negative site, e.g. a lone pair of a Lewis base or an anion.
Abstract: A σ-hole bond is a noncovalent interaction between a covalently-bonded atom of Groups IV–VII and a negative site, e.g. a lone pair of a Lewis base or an anion. It involves a region of positive electrostatic potential, labeled a σ-hole, on the extension of one of the covalent bonds to the atom. The σ-hole is due to the anisotropy of the atom's charge distribution. Halogen bonding is a subset of σ-hole interactions. Their features and properties can be fully explained in terms of electrostatics and polarization plus dispersion. The strengths of the interactions generally correlate well with the magnitudes of the positive and negative electrostatic potentials of the σ-hole and the negative site. In certain instances, however, polarizabilities must be taken into account explicitly, as the polarization of the negative site reaches a level that can be viewed as a degree of dative sharing (coordinate covalence). In the gas phase, σ-hole interactions with neutral bases are often thermodynamically unfavorable due to the relatively large entropy loss upon complex formation.
••01 Jan 2011
TL;DR: A review of the current state of knowledge of the fundamental sooting processes, including the chemistry of soot precursors, particle nucleation and mass/size growth, can be found in this article.
Abstract: Over the last two decades, our understanding of soot formation has evolved from an empirical, phenomenological description to an age of quantitative modeling for at least small fuel compounds. In this paper, we review the current state of knowledge of the fundamental sooting processes, including the chemistry of soot precursors, particle nucleation and mass/size growth. The discussion shows that though much progress has been made, critical gaps remain in many areas of our knowledge. We propose the roles of certain aromatic radicals resulting from localized π electron structures in particle nucleation and subsequent mass growth. The existence of these free radicals provides a rational explanation for the strong binding forces needed for forming initial clusters of polycyclic aromatic hydrocarbons. They may also explain a range of currently unexplained sooting phenomena, including the large amount of aliphatics observed in nascent soot formed in laminar premixed flames and the mass growth of soot in the absence of gas-phase H atoms. While the above suggestions are inspired, to an extent, by recent theoretical findings from the materials research community, this paper also demonstrates that the knowledge garnered through our longstanding interest in soot formation may well be carried over to flame synthesis of functional nanomaterials for clean and renewable energy applications. In particular, work on flame-synthesized thin films of nanocrystalline titania illustrates how our combustion knowledge might be useful for developing advanced yet inexpensive thin-film solar cells and chemical sensors for detecting gaseous air pollutants.
TL;DR: This discussion addresses the origins of σ holes, the factors that govern the magnitudes of their electrostatic potentials, and the properties of the resulting complexes with negative sites, and points out that σ-hole interactions are not limited to halogens, but can also involve covalently bonded atoms of Groups IV-VI.
Abstract: Halogen bonding is a noncovalent interaction that is receiving rapidly increasing attention because of its significance in biological systems and its importance in the design of new materials in a variety of areas, for example, electronics, nonlinear optical activity, and pharmaceuticals. The interactions can be understood in terms of electrostatics/polarization and dispersion; they involve a region of positive electrostatic potential on a covalently bonded halogen and a negative site, such as the lone pair of a Lewis base. The positive potential, labeled a σ hole, is on the extension of the covalent bond to the halogen, which accounts for the characteristic near-linearity of halogen bonding. In many instances, the lateral sides of the halogen have negative electrostatic potentials, allowing it to also interact favorably with positive sites. In this discussion, after looking at some of the experimental observations of halogen bonding, we address the origins of σ holes, the factors that govern the magnitudes of their electrostatic potentials, and the properties of the resulting complexes with negative sites. The relationship of halogen and hydrogen bonding is examined. We also point out that σ-hole interactions are not limited to halogens, but can also involve covalently bonded atoms of Groups IV-VI. Examples of applications in biological/medicinal chemistry and in crystal engineering are mentioned, taking note that halogen bonding can be "tuned" to fit various requirements, that is, strength of interaction, steric factors, and so forth.