Properties of halogen atoms for representing intermolecular electrostatic interactions related to halogen bonding and their substituent effects

The electrostatic properties of halogen atoms are studied theoretically in relation to their ability of halogen bonding, which is an attractive intermolecular interaction of a covalently bonded halogen atom with a negatively charged atom of a neighboring molecule. The electric quadrupole (of electronic origin) with a positive zz component Θ_zz of a covalently bonded halogen atom, where the z axis is taken along the covalent bond involving the halogen atom, is mainly responsible for the attractive electrostatic interaction with a negatively charged atom. This positive Θ_zz is an intrinsic property of halogen atoms with the p_x²p_y²p_z configuration of the valence electronic shell, as shown by ab initio molecular orbital calculations for isolated halogen atoms with this electronic configuration, and increases in the order of F < Cl < Br < I, in parallel with the known general sequence of the strength of halogen bonding. For halogen‐containing aromatic compounds, the substituent effects on the electrostatic properties are also studied. It is shown that the magnitude of Θ_zz and the electric field originating from it are rather insensitive to the substituent effect, whereas the electric field originating from atomic partial charges has a large substituent effect. The latter electric field tends to partially cancel the former. The extent of this partial cancellation is reduced in the order of Cl < Br < I and is also reducible by proper substitution on or within the six‐membered ring of halobenzene. Perspectives on the development of potential function parameters applicable to halogen‐bonding systems are also briefly discussed. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010     

Module Principle in Structure Formation Studies of Mercury Oxo and Chalcogen Halides

The role of large Cl, Br, and I anions in the structures of Hg₃X₂Hal₂ (X = S, Se, Te; Hal = Cl, Br, I) and some related compounds is analyzed. The structures consist of modules — cubic subcells of halogen atoms body-centered by X anions or covalently bound groups and face-centered by Hg atoms. The leading role of the anions is confirmed by the high occupancies of the halogen atoms in characteristic families of crystallographic planes and by the predominant location of halogen atoms in the special positions.     

Carbon-13 NMR spectra of polybromoalkanes and polychlorobromoalkanes. Structural increments of halogens in polyhalogenated groups

The ¹³C NMR spectra of 48 polychlorobromoalkanes have been studied. Unlike the ¹³C signals of chlorine-containing groups (38–105 ppm), those of bromine-containing fragments, with the exception of CBr₂ (60–70 ppm), appear in a rather narrow range (25–50 ppm) and are shifted to higher field in relation to similar chlorine-containing groups. The spin–spin coupling constants in similar bromine- and chlorine-containing groups practically coinciEN. Calculation of the chemical shifts for the polyhaloalkanes under study according to the additivity scheme, as previously observed for polychloroalkanes, renders values which are in considerable discord with experimental values (up to –32 ppm for CBr₃). These discrepancies may be compensated for by corrections for the binary interaction of halogen atoms by grouping the halogen-containing fragments according to the geminal, vicinal, 1,3-, 1,3,5- and 1,2,3-arrangement of halogen atoms, and by introducing an increment for the position of the halogen at the secondary atom. It is established that as compared to 1-monohaloalkanes: (a) in the case of the geminal arrangement of halogen atoms the α- and γ-effects diminish (Δ α from –3.2 to –8 ppm; Δγ = 2.6 ppm), while the β-effect increases slightly (from 0 to 1.2 ppm); (b) in the case of a vicinal arrangement both the α- and β-effects diminish (by about –3.5 ppm) and the γ-effect remains constant, as if the vicinal system of the halogens was topologically insulated; (c) for the 1,3- and 1,3,5-arrangement of halogens their mutual influence is weak (about –0.5 ppm for each halogen atom in the α- and γ-positions); (d) the 1,2,3 system (serial arrangement of halogen atoms) is the sum of two vicinal fragments and hardly deviates from the additivity scheme; (e) the arrangement of a halogen at the secondary C atom enhances the α-effect (Δα = 2.8 and 1.0 for methyl and methylene, respectively, in the case of Cl, and 3.5 and 3.7 ppm in the case of Br); the variation of the β-effect has a different sign in relation to CH₃ and CH₂ groups (+1.2 and –1.7 for Cl, and +2.5 and –1.0 for Br). More distant effects of halogens (δ and ?) were not considered. The determined increments (Δα, Δβ and Δγ) for the α-, β- and γ-effects of chlorine and bromine atoms allow the prediction of the 13^C chemical shifts in polyhaloalkanes with an accuracy up to ±1.5 ppm. Some deviations of up to ±5 ppm may be connected with the influence of a three particle interaction of halogen atoms, which was taken into account only in the case of a geminal arrangement of halogen atoms.     

Fragmentation of the adducts of perfluoromethyl vinyl ether with halo- and nitronium fluorosulfates under electron impact

Conclusions The mass spectra of CF₃OCF(OSO₂F)CF₂X (X=halogen, NO₂) and some model compounds have been studied. It has been established that the molecular cation-radicals of these compounds are not stable. The main breakdown processes of the even-electron fragment ions occur with migration of halogen atoms or fluorosulfate groups to neighboring carbon atoms.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimiya, No. 6, pp. 1311–1314, June, 1984.     

Halogen Bonding： An AIM Analysis of the Weak Interactions

A series of complexes formed between halogen-containing molecules and ammonia have been investigated by means of the atoms in molecules （AIM） approach to gain a deeper insight into halogen bonding. The existence of the halogen bond critical points （XBCP） and the values of the electron density （Pb） and Laplacian of electron density （V2pb） at the XBCP reveal the closed-shell interactions in these complexes. Integrated atomic properties such as charge, energy, polarization moment, volume of the halogen bond donor atoms, and the corresponding changes （△） upon complexation have been calculated. The present calculations have demonstrated that the halogen bond represents different AIM properties as compared to the well-documented hydrogen bond. Both the electron density and the Laplacian of electron density at the XBCP have been shown to correlate well with the interaction energy, which indicates that the topological parameters at the XBCP can be treated as a good measure of the halogen bond strength In addition, an excellent linear relationship between the interatomic distance d（X…N） and the logarithm of Pb has been established.     

Halogen bonding: a theoretical study based on atomic multipoles derived from quantum theory of atoms in molecules

Atomic multipole moments derived from quantum theory of atoms in molecules are used to study halogen bonds in dihalogens (with general formula YX, in which X refers to the halogen directly interacted with the Lewis base) and some molecules containing C–X group. Multipole expansion is used to calculate the electrostatic potential in a vicinity of halogen atom (which is involved in halogen bonding) in terms of atomic monopole, dipole, and quadrupole moments. In all the cases, the zz component of atomic traceless quadrupole moments (where z axis taken along Y–X or C–X bonds) of the halogens plays a stabilizing role in halogen bond formation. The effects of atomic monopole and dipole moments on the formation of a halogen bond in YX molecules depend on Y and X atoms. In Br₂ and Cl₂, the monopole moment of halogens is zero and has no contribution in electrostatic potential and hence in halogen bonding, while in ClBr, FBr, and FCl it is positive and therefore stabilize the halogen bonds. On the other hand, the negative sign of dipole moment of X in all the YX molecules weakens the corresponding halogen bonds. In the C–X-containing molecules, monopole and dipole moments of X atom are negative and consequently destabilize the halogen bonds. So, in these molecules the quadrupole moment of X atom is the only electrostatic term which strengthens the halogen bonds. In addition, we found good linear correlations between halogen bonds strength and electrostatic potentials calculated from multipole expansion.     

Intensity of N-O valence vibrations in nitroalkanes and halogen-substituted nitroalkanes

Summary The intensity of NO₂ group va'lence vibrations and, therefore, the electrooptical parameters of the N-O bond in nitroalkanes and halogen substituted nitro compounds is independent of the number of nitro groups and halogen atoms combined with the same carbon atom.     

Borane Derivatives: A New Class of Super‐ and Hyperhalogens

Super‐ and hyperhalogens are a class of highly electronegative species whose electron affinities far exceed those of halogen atoms and are important to the chemical industry as oxidizing agents, biocatalysts, and building blocks of salts. Using the well‐known Wade–Mingos rule for describing the stability of closo‐boranes B_nH_n^2? and state‐of‐the‐art theoretical methods, we show that a new class of super‐ and hyperhalogens, guided by this rule, can be formed by tailoring the size and composition of borane derivatives. Unlike conventional superhalogens, in which a central metal atom is surrounded by halogen atoms, the superhalogens formed according to the Wade–Mingos rule do not have to have either halogen or metal atoms. We demonstrate this by using B₁₂H₁₃ and its isoelectronic cluster CB₁₁H₁₂ as examples. We also show that while conventional superhalogens containing alkali atoms require at least two halogen atoms, a single borane‐like moiety is sufficient to give M(B₁₂H₁₂) clusters (M=Li, Na, K, Rb, Cs) superhalogen properties. In addition, hyperhalogens can be formed by using the above superhalogens as building blocks. Examples include M(B₁₂H₁₃)₂ and M(CB₁₁H₁₂)₂ (M=Li–Cs). This finding opens the door to an untapped source of superhalogens and weakly coordinating anions with potential applications.     

On the nature of haloform–aromatic complexes

A study of the correlation of haloform proton solvent shifts in 13 aromatichydrocarbons gives clear evidence that the nature of the interactions is predominantly dipole-induced dipole and not specific acid-base interactions. The presence of halogen bonding interactions between the halogen atoms and the π electrons are not detected for CHCl₃ and CHBr₃, and can only be present to a marginal extent for CHI₃. The ASIS effect is not related to the molar concentration of the aromatic solvents, and the effect of alkyl substituents is explained in terms of exctuded zones around the aromatic ring.     

All‐Metal Clusters that Mimic the Chemistry of Halogens

Owing to their s²p⁵ electronic configuration, halogen atoms are highly electronegative and constitute the anionic components of salts. Whereas clusters that contain no halogen atoms, such as AlH₄, mimic the chemistry of halogens and readily form salts (e.g., Na⁺(AlH₄)^?), clusters that are solely composed of metal atoms and yet behave in the same manner as a halogen are rare. Because coinage‐metal atoms (Cu, Ag, and Au) only have one valence electron in their outermost electronic shell, as in H, we examined the possibility that, on interacting with Al, in particular as AlX₄ (X=Cu, Ag, Au), these metal atoms may exhibit halogen‐like properties. By using density functional theory, we show that AlAu₄ not only mimics the chemistry of halogens, but also, with a vertical detachment energy (VDE) of 3.98 eV in its anionic form, is a superhalogen. Similarly, analogous to XHX superhalogens (X=F, Cl, Br), XAuX species with VDEs of 4.65, 4.50, and 4.34 eV in their anionic form, respectively, also form superhalogens. In addition, Au can also form hyperhalogens, a recently discovered species that show electron affinities (EAs) that are even higher than those of their corresponding superhalogen building blocks. For example, the VDEs of M(AlAu₄)₂^? (M=Na and K) and anionic (FAuF)? Au? (FAuF) range from 4.06 to 5.70 eV. Au‐based superhalogen anions, such as AlAu₄^? and AuF₂^?, have the additional advantage that they exhibit wider optical absorption ranges than their H‐based analogues, AlH₄^? and HF₂^?. Because of the catalytic properties and the biocompatibility of Au, Au‐based superhalogens may be multifunctional. However, similar studies that were carried out for Cu and Ag atoms have shown that, unlike AlAu₄, AlX₄ (X=Cu, Ag) clusters are not superhalogens, a property that can be attributed to the large EA of the Au atom.     

Coordination Polyhedra RhX6 (X = F,Cl, Br) in Crystal Structures

Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres were used to perform crystal-chemical analyses of compounds containing complexes [Rh _a X _n ] ^z– (X = F, Cl, Br). It was found that, irrespective of oxidation number (+3, +4, or +5), rhodium atoms always exhibit the coordination number 6 with respect to the halogen atoms and have octahedral coordination. The influence of site symmetry and the valence state of Rh on the distortion of RhX₆ octahedra are considered. The electronic configuration of the Rh atoms is shown to influence the symmetry of their valence-force field within the crystal structure.     

Stereochemical features of bromine- and iodine-containing compounds of lanthanides

The Voronoi-Dirichlet (VD) polyhedra and the intersecting spheres method have been used to analyze the features of the environment of lanthanide (Ln) atoms consisting of bromine and iodine atoms in the structures of 94 compounds containing 96 LnBr _n complexes and 41 LnI _n complexes. The lanthanum CN with respect to halogen atoms varies from 6 to 9. The volume of the VD polyhedra of Ln atoms depends only on the oxidation state of the metal atom and the nature of the surrounding atoms.     

Nontypical iodine–halogen bonds in the crystal structure of (3E)‐8‐chloro‐3‐iodomethylidene‐2,3‐dihydro‐1,4‐oxazino[2,3,4‐ij]quinolin‐4‐ium triiodide

Two kinds of iodine–iodine halogen bonds are the focus of our attention in the crystal structure of the title salt, C₁₂H₈ClINO⁺·I₃⁻, described by X‐ray diffraction. The first kind is a halogen bond, reinforced by charges, between the I atom of the heterocyclic cation and the triiodide anion. The second kind is the rare case of a halogen bond between the terminal atoms of neighbouring triiodide anions. The influence of relatively weakly bound iodine inside an asymmetric triiodide anion on the thermal and Raman spectroscopic properties has been demonstrated.     

Mechanisms of circumambulatory rearrangements of 5-halogeno-1,2,3,4,5-pentamethoxycarbonylcyclopentadienes

Possible paths of halogen atom migration in 5-halogeno-1,2,3,4,5-pentamethoxycarbonylcyclopentadienes were studied using the density functional theory. The calculations revealed preferential 1,5(in comparison with 1,3-) sigmatropic shifts of halogen atoms along the perimeter of the five-membered ring with the energy barriers ΔE _ZPE ^≠ = 42.9, 26.9, 19.8, and 15.4 kcal mol^–1 for the fluoro-, chloro-, bromo-, and iodosubstituted derivatives, respectively. The calculated charges of halogen atoms in the structures of transition states for 1,5-shifts change from negative for the fluorine atom to positive for the iodine atom (–0.356 (F), 0.019 (Cl), 0.052 (Br), 0.184 e (I)). The migration capacity increases in the order F < Cl < Br < I with an increase in the atomic radius of halogen.     

Aggregation of Halogen Atoms in Crystalline Isomers

A comparison of halogen (Hal) atom aggregation patterns was made for 26 groups of crystalline C _m H _n Hal _p isomers (position isomers with different locations of halogen atoms and/or alkyl/phenyl groups and stereoisomers were primarily compared). A total of 58 substances with low halogen contents are considered. It is found that crystals of some isomers with similar molecular structures have fully identical Hal aggregates. In most cases, however, the Halaggregation patterns turn out to be only partly similar; i.e., isomers have either the same type of aggregates (finite or infinite in one, two, or three dimensions) or close local characteristics, such as k(Hal) (coordination number of halogen atoms with respect to neighboring halogen atoms) and r (mean distance to k nearest neighbors). Different positions of methyl groups in isomer molecules have no effect on the characteristics of Hal aggregates in the examined substances, whereas different positions of ethyl and phenyl groups lead to significant changes in the Halaggregation pattern.     

Dramatically Enhanced Solubility of Halide‐Containing Organometallic Species in Diiodomethane: The Role of Solvent⋅⋅⋅Complex Halogen Bonding

In the current study, we evaluated the solubility of a number of organometallic species and showed that it is noticeably improved in diiodomethane when compared to other haloalkane solvents. The better solvation properties of CH₂I₂ were associated with the substantially better σ‐hole‐donating ability of this solvent, which results in the formation of uniquely strong solvent–(metal complex) halogen bonding. The strength of the halogen bonding is attenuated by the introduction of additional halogen atoms in the organometallic species owing to the competitive formation of more favourable intermolecular complex–complex halogen bonding. The exceptional solvation properties of diiodomethane and its inertness towards organometallic species make this solvent a good candidate for NMR studies, in particular, for the acquisition of spectra of insensitive spins.     

Inductive effects on molecular ionization potentials—X: Alkyl and hydrogen halides

The ionization potentials of alkyl and hydrogen halides are found to be excellent linear fractions of the polar and inductive substituent constants, indicating that the effect of alkyl substituents on the electron density of the halogen atoms is inductive. The slopes of the four regression lines vary widely in the order RF ? RCl > RBr > RI, which shows that the susceptibility of the halogen atoms to inductive effects varies in the same order. Values of σ_I and σ^* for alkyl groups not previously available are estimated.     

Selective Emergence of the Halogen Bond in Ground and Excited States of Noble‐Gas–Chlorine Systems

Molecular‐beam scattering experiments and theoretical calculations prove the nature, strength, and selectivity of the halogen bonds (XB) in the interaction of halogen molecules with the series of noble gas (Ng) atoms. The XB, accompanied by charge transfer from the Ng to the halogen, is shown to take place in, and measurably stabilize, the collinear conformation of the adducts, which thus becomes (in contrast to what happens for other Ng‐molecule systems) approximately as bound as the T‐shaped form. It is also shown how and why XB is inhibited when the halogen molecule is in the ³Π_u excited state. A general potential formulation fitting the experimental observables, based on few physically essential parameters, is proposed to describe the interaction accurately and is validated by ab initio computations.     

Phosphorus and Halogen Co‐Doped Graphene Materials and their Electrochemistry

Doping of graphene materials with heteroatoms is important as it can change their electronic and electrochemical properties. Here, graphene is co‐doped with n‐type dopants such as phosphorus and halogen (Cl, Br, I). Phosphorus and halogen are introduced through the treatment of graphene oxide with PX₃ gas (PCl₃, PBr₃, and PI₃). Graphene oxides are prepared through chlorate and permanganate routes. Detailed chemical and structural characterization demonstrates that the graphene sheets are covered homogeneously by phosphorus and halogen atoms. It is found that the amount of phosphorus and halogen introduced depends on the graphene oxide preparation method. The electrocatalytic effect of the resulting co‐doped materials is demonstrated for industrially relevant electrochemical reactions such as the hydrogen evolution and oxygen reduction reactions.