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The capacity of SX2 (X = F, Cl, and Br) to engage in different kinds of noncovalent bonds was investigated by ab initio calculations. SCl2 (SBr2) has two σ-holes upon extension of Cl (Br)-S bonds, and two σ-holes upon extension of S-Cl (Br) bonds. SF2 contains only two σ-holes upon extension of the F-S bond. Consequently, SCl2 and SBr2 form chalcogen and halogen bonds with the electron donor H2CO while SF2 forms only a chalcogen bond, i.e., no F···O halogen bond was found in the SF2:H2CO complex. The S···O chalcogen bond between SF2 and H2CO is the strongest, while the strongest halogen bond is Br···O between SBr2 and H2CO. The nature of these two types of noncovalent interaction was probed by a variety of methods, including molecular electrostatic potentials, QTAIM, energy decomposition, and electron density shift maps. Termolecular complexes X2S···H2CO···SX'2 (X = F, Cl, Br, and X' = Cl, Br) were constructed to study the interplay between chalcogen bonds and halogen bonds. All these complexes contained S···O and Cl (Br)···O bonds, with longer intermolecular distances, smaller values of electron density, and more positive three-body interaction energies, indicating negative cooperativity between the chalcogen bond and the halogen bond. In addition, for all complexes studied, interactions involving chalcogen bonds were more favorable than those involving halogen bonds. Graphical Abstract Molecular electrostatic potential and contour map of the Laplacian of the electron density in Cl2S···H2CO···SCl2 complex.

The positive electrostatic potentials (ESP) outside the σ-hole along the extension of OP bond in OPH3 and the negative ESP outside the nitrogen atom along the extension of the CN bond in NCX could form the Group V σ-hole interaction OPH3 ⋯NCX. In this work, the complexes NCY⋯OPH3 ⋯NCX and OPH3 ⋯NCX⋯NCY (X, YF, Cl, Br) were designed to investigate the enhancing effects of Y⋯O and X⋯N halogen bonds on the P⋯N Group V σ-hole interaction. With the addition of Y⋯O halogen bond, the VS, max values outside the σ-hole region of OPH3 becomes increasingly positive resulting in a stronger and more polarizable P⋯N interaction. With the addition of X⋯N halogen bond, the VS, min values outside the nitrogen atom of NCX becomes increasingly negative, also resulting in a stronger and more polarizable P⋯N interaction. The Y⋯O halogen bonds affect the σ-hole region (decreased density region) outside the phosphorus atom more than the P⋯N internuclear region (increased density region outside the nitrogen atom), while it is contrary for the X⋯N halogen bonds., (© 2015 Wiley Periodicals, Inc.)

Halogen-bonding interactions are highly directional intermolecular interactions that are often important in crystal engineering. In this work, the second-order Møller-Plesset perturbation theory (MP2) calculations and the quantum theory of "atoms in molecules" (QTAIM) and noncovalent interaction (NCI) studies were carried out on a series of X···N halogen bonds between substituted haloperfluoroarenes C6F4XY (X = Cl, Br, I; Y = F, CN, NO2) as bond donors and 1,2-diaminoethane as bond acceptor. Our research supports earlier work that electron-withdrawing substituents produce an enhancement effect on the size of the σ-hole and the maximum positive electrostatic potentials (VS,max), which further strengthens the halogen bonding. The metallic ion M(+) (M(+) = Li(+), Na(+)) has the ability to enhance the size of both the σ-hole and VS,max value with the formation of [MNCC6F4X](+), resulting in more electronic charge transfer away from the halogen atom X and an increase in the strength of the halogen bond. It is found that the values of V(S,max) at the σ-holes are linear in relation to the halogen-bonded interaction energies and the halogen-bonding interaction distance, indicating that the electrostatic interaction plays a key role in the halogen-bonding interactions. The values of V(S,max) at the σ-holes are also linear in relation to the electron density ρ(b), its Laplacian nabla(2)ρb, and -Gb/Vb of XB, indicating that the topological properties (ρb, nabla(2)ρb) and energy properties (Gb, Vb) at the BCPs are correlated with the electrostatic potentials.

The nature of the interactions of furan and thiophene with hydrogen halides and lithium halides has been investigated using ab initio calculations and QTAIM analysis. The concept of molecule formation density difference (MFDD) is introduced to study weak hydrogen bond (HB) and lithium bond (LB) interactions. The results have shown the molecular electrostatic potentials of furan and thiophene, as well as of the hydrogen halides and lithium halides, determine the geometries of the complexes. Both the studied HB and LB interactions can be classified as "closed-shell" weak interactions. The topological properties and energy properties at the bond critical points of HB and LB have been shown to be exponentially dependent on intermolecular distances d(H-bond) and d(Li-bond), which enables interpretation of the strength of the HB and LB interactions in terms of these ρ(r) properties. Electron transfer plays a more important role in the formation of HB than in that of LB, while electrostatic interaction in LB is more dominant than that in HB.

The halogen bonding of furan⋅⋅⋅XY and thiophene⋅⋅⋅XY (X=Cl, Br; Y=F, Cl, Br), involving σ- and π-type interactions, was studied by using MP2 calculations and quantum theory of "atoms in molecules" (QTAIM) studies. The negative electrostatic potentials of furan and thiophene, as well as the most positive electrostatic potential (V(S,max) ) on the surface of the interacting X atom determined the geometries of the complexes. Linear relationships were found between interaction energy and V(S,max) of the X atom, indicating that electrostatic interactions play an important role in these halogen-bonding interactions. The halogen-bonding interactions in furan⋅⋅⋅XY and thiophene⋅⋅⋅XY are weak, "closed-shell" noncovalent interactions. The linear relationship of topological properties, energy properties, and the integration of interatomic surfaces versus V(S,max) of atom X demonstrate the importance of the positive σ hole, as reflected by the computed V(S,max) of atom X, in determining the topological properties of the halogen bonds., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In gold(I) catalysis, the activation of Au(I) chloride catalysts via chloride abstraction and noncovalent interactions has become a research focus in organometallic catalysis. In this work, taking halogen bond donors (C4H2INO2, C6F5I, C8H9O2I) as activators for a Au(I) chloride catalyst (Ph3PAuCl), the mechanism of the cyclization reaction of propargylic amide was investigated. It was found that there are two activation modes as design principles to obtain the catalytically active species Ph3PAu+: the halogen bond donors activate the Cl atoms of Ph3PAuCl to form X–I⋯Cl (X = C, N) classical halogen bonds and activate the Au atoms of Ph3PAuCl to form X–I⋯Au (X = C, N) metal-involved halogen bonds. For the two activation modes, the mechanism of the cyclization reaction of propargylic amide has pathways: the chloride abstraction process of the first step and the 5-exo/6-endo cyclization process of the second step. Both activation modes show good activity for the cyclization reaction with the activation ability of classical halogen bonds being slightly stronger than that of the metal-involved halogen bonds, which is consistent with the strength of the X–I⋯Cl halogen bonds being slightly stronger than that of the X–I⋯Au halogen bonds. Therefore, both metal-involved halogen bonds and classical halogen bonds have important development prospects for the activation of catalysts in gold(I) catalysis. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: The carbonyl–olefin ring‐closing metathesis reactions have become a powerful tool for carbon‐carbon bond formation. In this work, the halogen bond catalysis and classical Lewis acid catalysis on the carbonyl–olefin ring‐closing metathesis reaction were investigated by density function theory. For both the halogen bond catalysis and classical Lewis acid catalysis, the carbonyl–olefin ring‐closing metathesis reaction occurs by [2 + 2]‐cycloaddition process and [2 + 2]‐cycloreversion process, the reaction energy barriers are low, therefore, it can be performed easily at room temperature. The essential difference of the two kinds of catalysts is that the catalytic mechanism of halogen bond catalysis is mainly contribution of electrostatic interaction, while that of classical Lewis acid catalysis is mainly catalyzed by orbital interaction. The halogen bond donor catalysts (ICl3, IF3) are expected to be efficient catalysts for the reaction and further promote the chemical synthesis of carbonyl–olefin ring‐closing metathesis reaction. [ABSTRACT FROM AUTHOR]

Recently, the halogen bonding catalysis in Aza‐Diels‐Alder reaction is increasing gloriously. In this work, the mechanism of the Aza‐Diels‐Alder reaction between imine and Danishefsky's diene catalyzed by N‐heterocyclic imidazole halogen bond donors has been explored with density functional theory. It is revealed that the reaction has two possible pathways: [4+2] cycloaddition pathway and Mannich pathway, in agreement with experimental predictions. Formation of halogen bond between the iodine atom of the catalysts and the N atom of the imine, results in lower energy barriers and more favorable of the reaction. The catalytic effect of the halogen bond can result in the electron rearrangement, which facilitates the formation of C−C bond. The stronger electron‐withdrawing ability of the group bonded to iodine atom of catalysts is, the better the catalytic activity is. These findings could be helpful to develop halogen bond donor catalysts in organic reactions. [ABSTRACT FROM AUTHOR]

The noncovalent interactions involving heteronuclear ethylene analogues H2CEH2 (E = Si, Ge and Sn) have been studied by the Møller–Plesset perturbation theory to investigate the competition and cooperativity between the hydrogen/halogen bond and π‐hole bond. H2CEH2 has a dual role of being a Lewis base and acid with the region of π‐electron accumulation above the carbon atom and the region of π‐electron depletion (π‐hole) above the E atom to participate in the NCX···CE (X = H and Cl) hydrogen/halogen bond and CE···NCY (Y = H, Cl, Li and Na) π‐hole bond, respectively. When HCN/ClCN interacts with H2CEH2 by two sites, the strength of hydrogen bond/halogen bond is stronger than that of π‐hole bond. The π‐hole bond becomes obviously stronger when the metal substituent of YCN (Y = Li and Na) interacting with H2CEH2, showing the character of partial covalent, its strength is much greater than that of hydrogen/halogen bond. In the ternary complexes, both hydrogen/halogen bond and π‐hole bond are simultaneously strengthened compared to those in the binary complexes, especially in the systems containing alkali metal. [ABSTRACT FROM AUTHOR]

The ability of C6F5X (X = Cl, Br, I) to favorably interact with ZH3 (Z = N, P, As) was evaluated at the level of M06-2X functional. For comparison, the C6F5I···ZPh3 (Z = N, P, As) complex was also studied. The halogen bond donors C6F5X (X = Cl, Br, I) have positive regions of electrostatic potentials (ESP) outside the X atom, and could interact with the negative ESP outside the Z atom of ZH3 (Z = N, P, As) to form the X···Z halogen bond. When the halogen bond donor remains unchanged, the halogen bond strength grows along the decreasing size of As, P, and N. When halogen bond acceptor remains unchanged, the halogen bond becomes stronger gradually along the sequence of X = Cl, Br, I. It was found that C6F5I···ZPh3 complex greatly reduces the strength of the halogen bond comparing with the C6F5I···ZH3. [ABSTRACT FROM AUTHOR]

In recent years, anion‐anion halogen bonds and neutral‐anion halogen bonds have received extensive attention. In this work, the possibility of halogen bonding of neutral and anionic forms of para‐substituted iodine derivatives of dithiobenzoic acid and its Se‐ and Te‐based congeners with halide anions has been investigated. The anion‐anion complexes are not favorable in the gas phase because of the repulsive effect between anionic halogen bond donors and acceptors. A local minimum is present in the potential energy surface between the −S2CC6H4I and X (X=F−, Cl−, Br−), and the anion‐anion complexes −S2CC6H4I ⋅⋅⋅ X(X=F−, Cl−, Br−) are metastable in the gas phase. Solvation is beneficial to the formation of the anion‐anion complexes. The neutral‐anion complexes are stable in both the gas phase and the polar solvents. The anion‐anion halogen bonds tend to be stable in polar solvents, while the neutral‐anion halogen bonds are stronger in the gas phase than in solvents. [ABSTRACT FROM AUTHOR]

The noncovalent interactions between the σ-hole region outside the halogen atom and the nitrogen atom of pyridine and its para-substituted derivatives are the focus of this work. Based on the analyses of the electrostatic potentials, YCF3 (Y = Cl, Br, I) act as halogen bond donors, XC5H4N (X = CH3, H, Cl, CN, NO2) act as halogen bond acceptors, and the binary halogen-bonded complexes XC5H4N···YCF3 have been designed and investigated by B3LYP-D3/aug-cc-pVDZ calculations together with the aug-cc-pVDZ-PP basis set for iodine. When the halogen bond acceptor remains unchanged, the interactions between C5H5N and YCF3 (Y = Cl, Br, I) increase with the order of Y = Cl, Br, and I. When the halogen donor ICF3 is fixed, the halogen bonding interactions decrease along the sequence of X = CH3, H, Cl, CN, NO2. Therefore, the halogen bond of the CH3C5H4N···ICF3 complex is the strongest. [ABSTRACT FROM AUTHOR]

The mechanism of ring‐opening polymerization of L‐lactide by iodine trichloride (ICl3) catalyst has been explored by using density functional theory (DFT) calculations and three catalytic pathways were proposed. The first and second pathways belong to the halogen bond catalysis, and the third pathway involves the ICl3 catalysts participating in reactions. When the carbonyl group was maintained involved in the reaction and activated catalytically by the halogen bond, there are two possible pathways. The first pathway involves only one transition state, and the second pathway requires two transition states. There is another pathway in which ICl3 directly participates in the reaction, it is named the third pathway. Two different transition states of the four‐membered rings are generated successively, the transfer of I─O bonds determined the progress of the reaction. Theoretical calculations in this work provide the most basic understanding of ring‐opening polymerization of L‐lactide by ICl3 catalysts. © 2019 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The positive electrostatic potentials (σ-hole) have been found in ylides CHXH (X = P, As, Sb) and CHYH (Y = S, Se, Te), on the outer surfaces of group VA and VIA atoms, approximately along the extensions of the C-X and C-Y bonds, respectively. These electrostatic potentials suggest that the above ylides can interact with nucleophiles to form weak, directional noncovalent interactions similar to halogen bonding interactions. MP2 calculations have confirmed the formation of CHXH···HM complexes (X = P, As, Sb; M = BeH, ZnH, MgH, Li, Na). The interaction energies, interaction distances, topological properties (electron density and its Laplacian), and energy properties (kinetic electron energy density and potential electron energy density) at the X(1)···H(10) bond critical points are all correlated with the most negative electrostatic potential value of HM, indicating that electrostatic interactions play an important role in these weak X···H interactions. Similar to the halogen bonding interactions, weak interactions involving ylides may be significant in several areas such as organic synthesis, crystal engineering, and design of new materials. [ABSTRACT FROM AUTHOR]

The character of the cooperativity between the HOX···OH/SH halogen bond (XB) and the Y-H···(H)OX hydrogen bond (HB) in OH/SH···HOX···HY (X = Cl, Br; Y = F, Cl, Br) complexes has been investigated by means of second-order Møller−Plesset perturbation theory (MP2) calculations and 'quantum theory of atoms in molecules' (QTAIM) studies. The geometries of the complexes have been determined from the most negative electrostatic potentials ( V) and the most positive electrostatic potentials ( V) on the electron density contours of the individual species. The greater the V values of HY, the larger the interaction energies of halogen-bonded HOX···OH/SH in the termolecular complexes, indicating that the ability of cooperative effect of hydrogen bond on halogen bond are determined by V of HY. The interaction energies, binding distances, infrared vibrational frequencies, and electron densities ρ at the BCPs of the hydrogen bonds and halogen bonds prove that there is positive cooperativity between these bonds. The potentiation of hydrogen bonds on halogen bonds is greater than that of halogen bonds on hydrogen bonds. QTAIM studies have shown that the halogen bonds and hydrogen bonds are closed-shell noncovalent interactions, and both have greater electrostatic character in the termolecular species compared with the bimolecular species. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Series of typical π-type and pseudo-π-type halogen-bonded complexes B ···ClY and B ···BrY and hydrogen-bonded complex B ···HY (B = C2H4, C2H2, and C3H6; Y = F, Cl, and Br) have been investigated using the MP2/aug-cc-pVDZ method. A striking parallelism was found in the geometries, vibrational frequencies, binding energies, and topological properties between B ···XY and B ···HY (X = Cl and Br). It has been found that the lengths of the weak bond d(X ···π)/ d(H ···π), the frequencies of the weak bond ν(X ···π)/ν(H ···π), the frequency shifts Δν(XY)/Δν(HY), the electron densities at the bond critical point of the weak bonds ρc(X ···π)/ρc(H ···π), and the electron density changes Δρc(XY)/Δρc(HY) could be used as measures of the strengths of typical π-type and pseudo-π-type halogen/hydrogen bonds. The typical π-type and pseudo-π-type halogen bond and hydrogen bond are noncovalent interactions. For the same Y, the halogen bond strengths are in the order B ···ClY < B ···BrY. For the same X, the halogen bond strength decreases according to the sequence F > Cl > Br that is in agreement with the hydrogen bond strengths B ···HF > B ···HCl > B ···HBr. All of these typical π-type and pseudo-π-type hydrogen-bonded and halogen-bonded complexes have the 'conflict-type' structure. Contour maps of the Laplacian of π electron density indicate that the formation of B ···XY halogen-bonded complex and B ···HY hydrogen-bonded complex is very similar. Charge transfer is observed from B to XY/HY and both the dipolar polarization and the volume of the halogen atom or hydrogen atom decrease on B ···XY/B ···HY complex formation. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

We present theoretical evidence that the two types of interactions exist in the complexes formed between methylenecyclopropane (MECP) and XY (X, Y = H, F, Cl, and Br). Two seats of XY interacted with MECP are located: (a) is via the pseudo‐π bonding electron pair associated with a CC bond of the cyclopropane ring and (b) is via the typical‐π bonding of electron pair of the CC bond of MECP. These two types of weak interactions are compared based on the calculated geometries, interaction energies, frequency changes, and topological properties of electron density. The integration of electron density over the interatomic surface is found to be a good measure for the strength of weak interaction. Furthermore, the total electron density and separated σ and π electron densities are also computed and discussed in this article. The separated electron density shows σ electron density determined the strength and π electron density influenced the direction of the hydrogen/halogen bond. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

Mechanisms of XN3 (X: F, Cl, Br, I) dissociations are proposed based on B3LYP calculated potential energy surfaces. The energy gaps between the ground-state reactants XN3(x˜ 1A′) and the intersystem crossing (ISC) points are only a little lower than respective potential energy barriers of the spin-allowed reactions, XN3(x˜ 1A′)→XN(a 1Δ)+N2(x˜ 1Σg+). The ISC point, therefore, is considered as a ‘transition state’ of the spin-forbidden reactions, XN3(x˜ 1A′)→XN(x˜ 3Σ−)+N2(x˜ 1Σg+). The methods of IRC and topological analysis of electron density are used to predict the thermal dissociation pathway of the reactions studied. [Copyright &y& Elsevier]

First-principles density functional theory calculations are employed to provide insight into the properties of metal- and halide-mixed perovskites, CH 3 NH 3 Sn 0.5 Pb 0.5 I 3−y X y (X = Br, Cl; y = 0.083, 0.167, 0.250, 0.333). The effects of halide substitutions on the structural, electronic, and optical properties, as well as the adsorptions of oxygen and water molecules on the surfaces of these perovskites are explored. • The substitution of I− with Cl− or Br− enlarges the band gap of MASn 0.5 Pb 0.5 I 3. • O 2 prefers to adsorb on Sn site, but H 2 O on Pb site of MASn 0.5 Pb 0.5 I 3−y X y (X = Cl, Br). • The halogen substitution can't bring the stabilization of perovskite in the moisture. First-principles density functional theory calculations are employed to provide insight into the structures and properties of metal- and halide-mixed perovskites, CH 3 NH 3 Sn 0.5 Pb 0.5 I 3−y X y (X = Br, Cl; y = 0.083, 0.167, 0.250, 0.333). Our calculations show that the substitution of I− with Cl− or Br− enlarges the band gap of the material, decreases the mobility of carriers and reduces the performance of the perovskites. The calculated absorption spectra show that a blue-shift occurs for the Cl−/Br− substituted perovskite, and the absorption intensity decreases with the increase of y value. Sn atom in the (0 0 1) surface of CH 3 NH 3 Sn 0.5 Pb 0.5 I 3−y X y (X = Cl, Br) is more attractive to the oxygen than the Pb atom, providing a reasonable explanation for the rapid oxidation of Sn2+ to Sn4+ observed experimentally. Unlike the O 2 molecule, H 2 O molecule prefers to adsorb on the Pb atom of the surface. The adsorption of water is much stronger than that of oxygen. Water is a critical factor of causing the degradation of the perovskites solar cell. [ABSTRACT FROM AUTHOR]