Diatomic Halogen Research Articles

Calculated Aqueous Reduction Potentials of Neutral and Anionic Halogen Diatomic Molecules.

The free energy of hydration, aqueous, and gas phase electron affinity and aqueous reduction potentials of F2, Cl2, Br2, I2, ClF, BrF, IF, BrCl, ICl, IBr, and their corresponding anions were calculated using an electronic structure approach previously developed for these properties for X• and XO•, where X is a halogen which yielded excellent results. The gas phase electron affinities were calculated at the Feller-Peterson-Dixon level based on complete basis set extrapolation of CCSD(T) results with additional corrections. The agreement with the available experimental data is excellent, and the calculations provide a complete set of reliable electron affinities for these diatomic halogens. The hybrid solvation approach uses single point implicit solvation calculations on gas phase optimized clusters with explicit solvent molecules. The gas phase energy calculations were performed using MP2 and CCSD(T)-F12b for tetramer clusters (four explicit waters) and MP2 for octamer clusters (eight explicit waters). The final redox potentials were obtained at the MP2/aug-cc-pVTZ (aT) with a self-consistent reaction field (SMD) level using the octamer clusters. The aqueous reduction potentials of the neutral diatomic halogens are predicted within 0.06 V of the experiment for diatomic neutrals. The same agreement of 0.06 V is predicted for the redox potential resulting from dissociation electron attachment of the diatomic halogen anions. The current work extends reduction potentials for multiple redox couples for which no experimental data is available, for example, those containing iodine and the interhalogen anions. F2•- is predicted to dissociate for its lowest energy structure in both the tetramer and octamer clusters to form solvated F-, HF, and OH•.

Structural, Electronic and Vibrational Properties of B24N24 Nanocapsules: Novel Anodes for Magnesium Batteries

We report on DFT-TDDFT studies of the structural, electronic and vibrational properties of B24N24 nanocapsules and the effect of encapsulation of homonuclear diatomic halogens (Cl2, Br2 and I2) and chalcogens (S2 and Se2) on the interaction of the B24N24 nanocapsules with the divalent magnesium cation. In particular, to foretell whether these BN nanostructures could be proper negative electrodes for magnesium-ion batteries, the structural, vibrational and electronic properties, as well as the interaction energy and the cell voltage, which is important for applications, have been computed for each system, highlighting their differences and similarities. The encapsulation of halogen and chalcogen diatomic molecules increases the cell voltage, with an effect enhanced down groups 16 and 17 of the periodic table, leading to better performing anodes and fulfilling a remarkable cell voltage of 3.61 V for the iodine-encapsulated system.

Reversible Cl/Cl- redox in a spinel Mn3O4 electrode.

A unique prospect of using halides as charge carriers is the possibility of the halides undergoing anodic redox behaviors when serving as charge carriers for the charge-neutrality compensation of electrodes. However, the anodic conversion of halides to neutral halogen species has often been irreversible at room temperature due to the emergence of diatomic halogen gaseous products. Here, we report that chloride ions can be reversibly converted to near-neutral atomic chlorine species in the Mn3O4 electrode at room temperature in a highly concentrated chloride-based aqueous electrolyte. Notably, the Zn2+ cations inserted in the first discharge and trapped in the Mn3O4 structure create an environment to stabilize the converted chlorine atoms within the structure. Characterization results suggest that the Cl/Cl- redox is responsible for the observed large capacity, as the oxidation state of Mn barely changes upon charging. Computation results corroborate that the converted chlorine species exist as polychloride monoanions, e.g., [Cl3]- and [Cl5]-, inside the Zn2+-trapped Mn3O4, and the presence of polychloride species is confirmed experimentally. Our results point to the halogen plating inside electrode lattices as a new charge-storage mechanism.

SbCl4: An Exceptional Superhalogen as the Building Block of a Mixed Valence Supercrystal with Unconventional Ferroelectricity.

Superhalogens are nanoclusters with high electron affinities, exhibiting behavior similar to that of halogens. Their dimerization yields nonpolar symmetrical clusters, akin to diatomic halogen molecules, and they are unstable in the condensed phase in the absence of charge-compensating cations. Herein, we provide ab initio evidence that SbCl4 superhalogen is an exception: its dimerization yields a polar cluster that can be viewed as a quasi-bonded [SbCl5]δ- and [SbCl3]δ+ Lewis acid-base cluster. The symmetry breaking arises from the valence stratification of Sb into Sb5+ and Sb3+ as well as their lone pair electrons. When assembled, SbCl4 clusters form a supercrystal that is thermodynamically stable up to 600 K, with the unique bonding feature of Sb2Cl8 prevailing in the bulk phase. Combination of mixed valence and lone pair electrons leads to electric polarizations along all directions, generating a type of unconventional multimode ferroelectricity in which three different modes of ferroelectricity with distinct magnitudes and Curie temperature are revealed.

Paradigms and paradoxes: the ionization potential of atomic astatine (Z =85), polonium (Z = 84), and some other elements—what does this value tell us about the energetics of atomic and diatomic halogens

The newly measured ionization potential of atomic astatine is discussed and compared with that of the recently determined value for polonium and for the other atomic halogens. Regularities in these atomic values are discussed and applied to the understanding of the energetics of diatomic halogens. Some surprises remain.

Quantum Monte Carlo Study of the Water Dimer Binding Energy and Halogen-π Interactions.

Halogen-π systems are involved with competition between halogen bonding and π-interaction. Using the diffusion quantum Monte Carlo (DMC) method, we compare the interaction of benzene with diatomic halogens (X2: Cl2/Br2) with the typical hydrogen bonding in the water dimer, taking into account explicit correlations of up to three bodies. The benzene-Cl2/Br2 binding energies (13.07 ± 0.42/16.62 ± 0.02 kJ/mol) attributed to both halogen bonding and dispersion are smaller than but comparable to the typical hydrogen bonding in the water dimer binding energy (20.88 ± 0.27 kJ/mol). All of the above values are in good agreement with those from the coupled-cluster with single, double, and noniterative triple excitations (CCSD(T)) results at the complete basis set limit (benzene-Cl2/Br2: 12.78/16.17 kJ/mol; water dimer: 21.0 kJ/mol).

Molecular Beam Scattering Experiments as a Sensitive Probe of the Interaction in Bromine-Noble Gas Complexes.

This paper reports for the first time molecular beam experiments for the scattering of He, Ne, and Ar by the Br2 molecule, with the aim of probing in detail the intermolecular interaction. Measurements have been performed under the experimental condition to resolve the glory pattern, a quantum interference effect observable in the collision velocity dependence of the integral cross section. We analyzed the experimental data with a reliable potential model defined as a combination of an anisotropic van der Waals component with the additional contribution due to charge transfer and polar flattening effects related to the formation of an intermolecular halogen bond. The model involves few parameters, whose values are related to fundamental physical properties of the interacting partners, and it allows an internally consistent comparison of the stability of the gas-phase adducts formed by Br2 moiety with different noble gases as well as homologous complexes with the Cl2 molecule. The same model appears to be also easily generalized to describe the interaction of diatomic halogen molecules in the excited B(3Π) electronic state where the halogen bond contribution tends to vanish and more anisotropic van der Waals components dominate the structure of the complexes with noble gases.

Halogenation of graphene triggered by heteroatom doping

Halogenation is one of the most important ways to tailor the properties of graphene. We demonstrate for the first time that boron and nitrogen doping can effectively tune the interactions between halogen diatomic molecules and graphene from first principles calculations. Boron and nitrogen doping disrupt the regular pi-electron pattern and create spin density and orbital polarization. More interesting, nitrogen and boron doping not only significantly increases the binding energies of Cl2, Br2, and I2 but also induces the spontaneous dissociation of F2. The tunable effects from nitrogen and boron doping can adjust the interactions in a wide range. Overall, it is suggested that doping can be a very promising method for the facile halogenation of graphene.

Bonding in the metallic molecular solid α-Gallium

ABSTRACTSolid, liquid and alloyed phases of gallium play a role in a variety of important technological applications. While many of the gallium phases involved in these applications are metallic, some have been proposed or are known to contain covalently bound Ga dimers. Thus, understanding the nature of bonding in Ga is crucial to the development of Ga-based materials. The solid phase of gallium at ambient conditions, α-Ga, is metallic and composed of molecular dimers, and can serve as a testing ground for studying gallium bonding with electronic structure calculations. We use density functional theory-based molecular dynamics simulations in conjunction with maximally localised Wannier functions to examine the nature of chemical bonding in α-Ga. We propose a geometric criterion for defining various bonding environments, which enables the quantification of covalent and weak bonds in solid gallium. We additionally connect the bonding structure of α-Ga to its phonon density of states and discuss similarities and differences with diatomic halogen crystals.

Adsorption of dihalogen molecules on pristine graphene surface: Monte Carlo and molecular dynamics simulation studies.

Weak interactions of graphene surface with reactive molecular impurities are the subject of many studies since noncovalent functionalization of surface via molecular doping is a powerful tool for tuning the electronic properties of graphene layers. In this work, the adsorption of diatomic halogen gas molecules, F2, Cl2, Br2, I2 onto bilayer and multilayer pristine graphene surfaces were studied comparatively by Monte Carlo (MC) and molecular dynamics (MD) simulation techniques in canonical ensemble. The adsorption sites, adsorption capacity, coverage factors, adsorption isotherms, and adsorption kinetics were investigated and the adsorption energies were calculated for all adsorbates. Graphene was modeled as a two-dimensional layer of 200 carbon atoms in a honeycomb arrangement. The COMPASS force field was used in the simulations. The adsorption isotherms were obtained and fitted to Langmuir model. The kinetics of adsorption was studied and found to be first order. Both the monolayer and the multilayer adsorption of halogen molecules showed that van der Waals volumes of halogen molecules and also their polarizabilities display a competitive role in the saturation capacity and the strength of surface interactions.

Size-dependent conformational change in halogen–π interaction: from benzene to graphene

Diatomic halogen molecules X2 (X = Cl/Br) favor the edge-to-face conformation on benzene with significant electrostatic interaction via halogen bonding. In contrast, they favor the stacked conformation on graphene with negligible electrostatic interaction. As the aromatic ring expands, the inner facial side becomes almost electrostatically neutral. On coronene, the two conformations are compatible.

A post‐HF study on the halogen bonding interaction of pyrene with diatomic halogen molecules

We present a detailed SCS‐MP2 study on the potential energy curves (PEC) for interactions between diatomic halogen molecules and pyrene. BSSE corrected CCSD[T] energies at equilibrium distances are computed and compared to CCSD(T) energies. The most stable conformation of these weakly bound van der Waals complexes is almost linear in the perpendicular direction to the pyrene plane. The complexes of highly polarizable bromine and iodine molecules with pyrene are very stable and they carry rather large number of vibrational states. Despite its small size, F2 also forms strong halogen bonding similar to Br2 and I2. The interaction between Cl2 and pyrene is the weakest and it is attributed to the highest polarizability/molar mass ratio of chlorine among the others. I2‐pyrene is found to be the most stable complex due to the strongest mutual polarization effects and is carrying more than 60 vibrational states. Due to the rather large number of electrons in some complexes, the relativistic corrections are also considered. © 2016 Wiley Periodicals, Inc.

Predictive Models for Halogen-bond Basicity of Binding Sites of Polyfunctional Molecules.

Halogen bonding (XB) strength assesses the ability of an electron-enriched group to be involved in complexes with polarizable electrophilic halogenated or diatomic halogen molecules. Here, we report QSPR models of XB of particular relevance for an efficient screening of large sets of compounds. The basicity is described by pKBI2 , the decimal logarithm of the experimental 1 : 1 (B : I2 ) complexation constant K of organic compounds (B) with diiodine (I2 ) as a reference halogen-bond donor in alkanes at 298 K. Modeling involved ISIDA fragment descriptors, using SVM and MLR methods on a set of 598 organic compounds. Developed models were then challenged to make predictions for an external test set of 11 polyfunctional compounds for which unambiguous assignment of the measured effective complexation constant to specific groups out of the putative acceptor sites is not granted. At this stage, developed models were used to predict pKBI2 of all putative acceptor sites, followed by an estimation of the predicted effective complexation constant using the ChemEqui program. The best consensus models perform well both in cross-validation (root mean squared error RMSE=0.39-0.47 logKBI2 units) and external predictions (RMSE=0.49). The SVM models are implemented on our website (http://infochim.u-strasbg.fr/webserv/VSEngine.html) together with the estimation of their applicability domain and an automatic detection of potential halogen-bond acceptor atoms.

ChemInform Abstract: Highly Regio‐ and Diastereoselective Formation of Tetrasubstituted (Z)‐1,2‐Dihaloalkenes from the Halogenation of Trimethylsilyl Alkynes with ICl.

The stereoselective anti addition of diatomic halogens to alkynes has been well studied. A method is reported that utilizes the β-silyl effect to override this typically observed anti selectivity and provides halogenation products that result from syn addition. The reaction involves the addition of iodine monochloride to trialkylsilyl-substituted alkynes to produce tetrasubstituted (Z)-dihaloalkenes in good to excellent yields and with excellent regio- and diastereoselectivity.

Highly Regio- and Diastereoselective Formation of Tetrasubstituted (Z)-1,2-Dihaloalkenes from the Halogenation of Trimethylsilyl Alkynes with ICl.

The stereoselective anti addition of diatomic halogens to alkynes has been well studied. A method is reported that utilizes the β-silyl effect to override this typically observed anti selectivity and provides halogenation products that result from syn addition. The reaction involves the addition of iodine monochloride to trialkylsilyl-substituted alkynes to produce tetrasubstituted (Z)-dihaloalkenes in good to excellent yields and with excellent regio- and diastereoselectivity.

High-performance dye-sensitized solar cells using edge-halogenated graphene nanoplatelets as counter electrodes

Edge-selectively halogenated graphene nanoplatelets (XGnPs, X=Cl, Br, and I) were prepared by the mechanochemically driven reaction between graphite and diatomic halogen molecules (Cl2, Br2 or I2). The contents of halogens (Cl, Br, and I) in XGnPs were 3.18, 1.77, and 0.66at%, respectively, by X-ray photoelectron spectroscopy. The XGnPs as counter electrodes (CEs) showed remarkably enhanced electrocatalytic activities toward Co(bpy)33+ reduction reaction in dye-sensitized solar cells (DSSCs) with an excellent electrochemical stability. Amongst XGnPs, IGnP-CE demonstrated the lowest charge-transfer resistance (Rct) of 0.46Ωcm2 at the CE/electrolyte interface. This value is much lower than that of Pt-CE (0.81Ωcm2). In addition, the DSSC with IGnP-CE had the highest fill factor (71.3%) and cell efficiency (10.31%), whereas those of DSSCs with Pt-CE were only 70.6% and 9.92%, respectively.

Dissociation of homonuclear diatomic halogens via multireference coupled cluster calculations

We have computed the potential energy surfaces (PESs) of F2, Cl2, Br2, and I2 using the size-extensive state specific multireference coupled cluster (SS-MRCC) method. The MR character of the system considered here at large distances and the presence of low-lying intruder states are known to be the major causes of incorrect or inaccurate predictions of the PES. The SS-MRCC theory is tailored to treat degeneracies of varying extent while bypassing the intruder problem. The quality of the computed PES has been gauged by computing spectroscopic constants. The calculated properties show a good agreement with available experimental data and the errors in the calculated molecular properties compare favourably with the most elaborate current-generation calculations of the literature. The accuracy of the computed PES of F2 is such that it has been proved to calculate the vibrational spectrum of the 22 levels with a minimum and maximum absolute deviation of 2 and 57 cm−1, respectively, from the experimental values. The highly satisfactory performance of the SS-MRCC method, vis-a-vis the other sophisticated methods, in describing the vibrational levels is noticeable for one of the more difficult systems such as F2 clearly indicates that the present method is reliable in studying the vibrational energy levels.

Charge transport in graphene doped with diatomic halogen molecules (I2, Br2) near Dirac point

We have investigated the transport properties of monolayer graphene doped with halogen molecules, iodine and bromine. For these doping, the charge neutrality point shifts to the hole carrier regime indicating p-type doping, and the carrier mobility is reduced. As compared to doping with other dopants, however, the reduction of the mobility is much weaker for doping with halogen molecules. Also, the minimum conductivities at the charge neutrality point are enhanced with subsequent doping for the monolayer graphene, in strong contrast to the cases with other dopants. When the graphene layer was doped selectively by covering its edge with a polymer layer, such unconventional behaviors were not observed any more. These observations can be understood that intercalated halogen molecules between the graphene layer and the underlying substrate leads to screening of charged impurities embedded in SiO2 substrate. Halogen molecules can be effective dopants for the graphene monolayer which changes the carrier concentration without significant degrading of the mobility.

Modulated structure and molecular dissociation of solid chlorine at high pressures

Among diatomic molecular halogen solids, high pressure structures of solid chlorine (Cl(2)) remain elusive and least studied. We here report first-principles structural search on solid Cl(2) at high pressures through our developed particle-swarm optimization algorithm. We successfully reproduced the known molecular Cmca phase (phase I) at low pressure and found that it remains stable up to a high pressure 142 GPa. At 150 GPa, our structural searches identified several energetically competitive, structurally similar, and modulated structures. Analysis of the structural results and their similarity with those in solid Br(2) and I(2), it was suggested that solid Cl(2) adopts an incommensurate modulated structure with a modulation wave close to 2∕7 in a narrow pressure range 142-157 GPa. Eventually, our simulations at >157 GPa were able to predict the molecular dissociation of solid Cl(2) into monatomic phases having body centered orthorhombic (bco) and face-centered cubic (fcc) structures, respectively. One unique monatomic structural feature of solid Cl(2) is the absence of intermediate body centered tetragonal (bct) structure during the bco → fcc transition, which however has been observed or theoretically predicted in solid Br(2) and I(2). Electron-phonon coupling calculations revealed that solid Cl(2) becomes superconductors within bco and fcc phases possessing a highest superconducting temperature of 13.03 K at 380 GPa. We further probed the molecular Cmca → incommensurate phase transition mechanism and found that the softening of the A(g) vibrational (rotational) Raman mode in the Cmca phase might be the driving force to initiate the transition.

Comment on “Ab initio molecular dynamics calculation of ion hydration free energies” [J. Chem. Phys. 130, 204507 (2009)

We suggest that the authors compare their theoretical Gibbs free energies −ΔGhyd (kcal/mol) Li+, 128(1), 135; Cl−, 78(1), 70(2); and Ag+, 120(1) to recent absolute experimental values Li+, 128; Cl−, 74; and Ag+, 119 kcal/mol referenced to that for H+, 266(2) kcal/mol. We present bulk Gibbs hydration free energies and ionic radii for other ions from aqueous electron affinities, monohydration free energies, and diatomic halogen anion potential energy curves consistent with the Born dielectric constant, 3.4, for electrons and protons.