Formation Of Halogen Research Articles

Assembling molecular Sierpiński triangle fractals.

Fractals, being "exactly the same at every scale or nearly the same at different scales" as defined by Benoit B. Mandelbrot, are complicated yet fascinating patterns that are important in aesthetics, mathematics, science and engineering. Extended molecular fractals formed by the self-assembly of small-molecule components have long been pursued but, to the best of our knowledge, not achieved. To tackle this challenge we designed and made two aromatic bromo compounds (4,4″-dibromo-1,1':3',1″-terphenyl and 4,4‴-dibromo-1,1':3',1″:4″,1‴-quaterphenyl) to serve as building blocks. The formation of synergistic halogen and hydrogen bonds between these molecules is the driving force to assemble successfully a whole series of defect-free molecular fractals, specifically Sierpiński triangles, on a Ag(111) surface below 80 K. Several critical points that govern the preparation of the molecular Sierpiński triangles were scrutinized experimentally and revealed explicitly. This new strategy may be applied to prepare and explore various planar molecular fractals at surfaces.

Influence of the halogen substituent on the formation of halogen and hydrogen bonding in co-crystals formed from acridine and benzoic acids

A series of nine co-crystals formed from acridine and benzoic acids have been synthesized and structurally characterized and the influence of the halogen substituent on the formation of halogen and hydrogen bonding in the co-crystals of the title compounds has been investigated.

2-Halogenoimidazolium salt catalyzed aza-Diels-Alder reaction through halogen-bond formation.

2-Halogenoimidazolium salts are found to catalyze aza-Diels-Alder reaction of aldimines with Danishefsky diene in an efficient manner. Comparative studies and titration experiments support the formation of halogen bonding between imines and catalysts.

A new oxo centered basic p-chlorobenzoate bridging heterotrinuclear complex, [Cr2MnO(C7H4O2Cl)6(Py)3]C7H5O2Cl: Synthesis, X-ray crystal structure and theoretical DFT study

The direct reaction between p-chlorobenzoic acid and metal nitrate salts resulted in the formation of a novel heterometallic μ3-oxo trinuclear cluster with the formula [CrIII2MnIIO(C7H4O2Cl)6(Py)3]C7H5O2Cl (1), which has been characterized by elemental analysis, electronic and IR spectra, and single-crystal X-ray crystallography. The electronic spectrum of the complex exhibited two spin-allowed bands for CrIII in the regions 17900 and 22750cm−1, which could be assigned to the transitions from 4A2g(F) to 4T2g(F) and 4T1g(F), respectively. We have also examined the Cambridge Structural Database to investigate the abundance of this type of complex in terms of the trivalent/divalent metal ions and the hetero/homometallic nature of the trinuclear cluster. We have studied the relative stability of the different cluster situations, calculating the energetic costs of a series of metal substitution reactions by means of high level DFT calculations. Moreover, we have analyzed the effect of the p-chlorine substituent in benzoic acid, since the formation of halogen bonding interactions in the solid state are important in determining the crystal packing of 1.

Exploring Supramolecular Self-Assembly of Metalloporphyrin Tectons by Halogen Bonding. 2

In expansion of earlier observations, one SnIV(L)2, one oxo–VIV, and nine oxo–MoV(L) new porphyrin compounds (L = anionic axial ligand) have been synthesized and structurally characterized by single crystal X-ray diffraction analysis to probe the occurrence of halogen bonds in crystalline metalloporphyrin assemblies. The [Sn(TIPP)(p-NO2-phenolate)2] six-coordinate system (TIPP = dianion of 5,10,15,20-meso-tetrakis(4-iodophenyl)porphyrin) (1) exhibits weak I···O interactions, stimulating further studies with the oxo–Mo/V porphyrin scaffolds. The domed complex [V(O)(TIPP)] (2) crystallizes in a chiral space group and shows short O···π contacts along the polar axis, but no distinct halogen bonds. In [Mo(O)(TIPP)(L)] (L = 1-hydroxybenzotriazolate (3), 5-bromonicotinate (4), pyrimidine-5-carboxylate (5), 4-iodobenzoate (6), 2-chlorobenzoate (7)) diverse (O···I, N···I, I···I) halogen bonds and halogen-bonding-type contacts have been observed, depending upon the nature of the axial ligand attached to the Mo center. In analogous compounds with TBrPP, [Mo(O)(TBrPP)(L)] (TBrPP = dianion of 5,10,15,20-meso-tetrakis(4-bromophenyl)porphyrin, L = 5-bromonicotinate (8), isonicotinate (9)), directional halogen interactions involving bromine have not been detected. Intermolecular N···I halogen bonding has also been observed when the N-donor sites were positioned on the porphyrin periphery and the iodine acceptor on the axial ligand as in [Mo(O)(T4pyP)(4-iodobenzoate)] (10) (T4pyP = dianion of 5,10,15,20-meso-tetrakis(4-pyridyl)porphyrin). An attempt to induce the formation of halogen bonded chain assemblies through I···O interaction between the axial oxo and iodine sites of adjacent species in [Mo(O)(TTP)(4-iodobenzoate)] (11) (TTP = dianion of 5,10,15,20-meso-tetrakis(p-tolyl)porphyrin) has not been successful.

The effect of C−H···O bonding and Cl···π interactions in electrocatalytic dehalogenation of C2 chlorides containing an acidic hydrogen

A tungsten alkoxy scorpionate shows activity in the electrocatalytic reductive dehalogenation of pentachloroethane and trichloroethylene owing to the formation of hydrogen and halogen bonded adducts with the substrates, which is further reinforced by dispersive interactions. The ensuing proximity between the substrate molecule and the metal centre promotes dechlorination in a concerted process. Two-electron reduction of pentachloroethane yields trichloroethylene that undergoes further, non-catalysed, reactions that ultimately give acetylenes. Interestingly, pentachloroethane proved to be a highly efficient proton donor for the transient anions, in extremely exothermic and rapid proton transfer concerted with chloride anion abstraction, which yields perchloroethylene. The total process and the mechanism thereof were verified based on DFT and coupled cluster (CC) calculations. The calculations evaluated feasibility of various pathways in the mechanism. Standard redox potentials for the environmentally relevant species, participating in the studied reactions, were accurately computed employing the explicitly correlated CCSD(T)-F12 method that provides an improved C-Cl bond energy, of essential importance to the dissociative potentials.

Halogen-Bonding Complexes Based on Bis(iodoethynyl)benzene Units: A New Versatile Route to Supramolecular Materials

Iodoalkynes [1,4-bis(iodoethynyl)benzene (p-BIB) and 1,3-bis(iodoethynyl)benzene (m-BIB)] have been used successfully to prepare halogen bonding complexes with a range of 4-pyridine derivatives showing liquid crystalline organizations. The trimeric halogen-bonded complexes obtained from p-BIB have a rod-like structure and exhibited high order calamitic phases (SmB and G). In contrast, m-BIB gives rise to bent-shaped structures that display SmAP-like mesophases. Furthermore it was found that the presence of three and five aromatic rings in these halogen-bonding complexes promotes calamitic mesophases while seven rings are required to stabilize bent-core mesophases. The formation of halogen bonding in the complexes was confirmed by several techniques, including FT-IR, XPS, and single crystal X-ray diffraction and the strength of the bonds was evaluated by DFT calculations

Experimental Characterization of C–X···Y–C (X = Br, I; Y = F, Cl) Halogen–Halogen Bonds

Using FTIR and Raman spectroscopy, we investigated the formation of halogen bonded complexes of the trifluorohalomethanes CF3Cl, CF3Br, and CF3I with the halomethanes CH3F and CH3Cl and the haloethanes C2H5F and C2H5Cl dissolved in liquid krypton. For CF3Br and CF3I, evidence was found for the formation of C-X···F and C-X···Cl halogen bonded 1:1 complexes. Using spectra recorded at different temperatures, we determined the complexation enthalpies for the complexes to be -7.0(3) kJ mol(-1) for CF3Br·CH3F, -7.6(1) kJ mol(-1) for CF3I·CH3F, -5.9(2) kJ mol(-1) for CF3Br·CH3Cl, -8.3(3) kJ mol(-1) for CF3I·CH3Cl, -7.1(1) kJ mol(-1) for CF3Br·C2H5F, -8.7(2) kJ mol(-1) for CF3I·C2H5F, -6.5(2) kJ mol(-1) for CF3Br·C2H5Cl, and -8.8(3) kJ mol(-1) for CF3I·C2H5Cl. For all halogen bonded complexes with a fluorine-electron donor, a blue shift ranging from +0.6 to +1.5 cm(-1) was observed for the C-X stretching mode. The results from the cyrospectroscopic study are compared with ab initio calculations at the MP2/aug-cc-pVDZ(-PP) level.

Role of chloroform and dichloromethane solvent molecules in crystal packing: an interaction propensity study

Using the Cambridge Structural Database (CSD), it is shown that the acidic C-H donors of chloroform and dichloromethane, respectively, form hydrogen bonds with N, O, S, halides or carbon-bound halogens in 82% and 77% of structures in which such interactions can occur. This hydrogen-bond potency is retained to a significant degree even in the presence of the more conventional O-H and N-H donors. The hydrogen-bond propensities exhibited by the C-H protons in CHCl3 and CH2Cl2 are similar to those of the acetylenic C-C≡C-H proton. However, involvement of the Cl atoms of CHCl3 and CH2Cl2 in non-bonded interactions is rather limited: the propensities for formation of (O or N)-H...Cl bonds are only 6% in both cases, while the propensities for the formation of halogen-halogen bonds is generally < 15%, with only Cl...Br interactions having slightly higher values. While C(phenyl)-H...Cl interactions are commonly observed, they are of low propensity and have distances at the upper end of the van der Waals limit. We conclude that the acidic C-H protons in chloroform and dichloromethane solvent molecules play a clear role in the involvement of these molecules in molecular aggregation in crystal structures, and this is exemplified by hydrogen-bond predictions made using the statistical propensity tool which is now part of the CSD system.

Exploring the C-X…π Halogen Bonding Motif: An Infrared and Raman Study of the Complexes of CF3X (X = Cl, Br and I) with the Aromatic Model Compounds Benzene and Toluene

The formation of halogen bonded complexes formed between the trifluorohalomethanes CF3Cl, CF3Br and CF3I and the Lewis bases benzene and toluene at temperatures below 150K was investigated using FTIR and Raman spectroscopy. Experiments using liquid krypton as solvent show that for both CF3Br and CF3I substantial fractions of the monomers can be involved in 1:1 complexes. In addition, weak absorptions illustrating the formation of 2:1 complexes between CF3I and benzene are observed. Using spectra recorded at temperatures between 120 and 140 K, observed information on the relative stability was obtained for all complexes by determining the complexation enthalpies in solution. The resulting values for CF3Br·benzene, CF3I·benzene and (CF3I)2·benzene are −6.5(3), −7.6(2) and −14.5(9) kJ mol−1. The values for CF3Br·toluene and CF3I·toluene are −6.2(5) and −7.4(5) kJ mol−1. The experimental complexation enthalpies are compared with theoretical data obtained by combining results from MP2/aug-cc-pVDZ(-PP) and MP2/aug-cc-pVTZ(-PP) ab initio calculations, from statistical thermodynamical calculations and from Monte Carlo Free Energy Perturbation simulations. The data are also compared with results derived for other C-X···π halogen bonded complexes involving unsaturated Lewis bases such as ethene and ethyne.

Superalkali Li3M (M = Cl, Br, I) as a Lewis base in halogen bonding: A heavier halogen is a stronger Lewis base than a lighter halogen

The Li3M–XY (M=Cl, Br, and I; XY=ClCl, BrBr, ClF, BrCl, and BrF) complexes have been studied with theoretical calculations at the MP2/aug-cc-pVTZ level. The results showed that the Br atom in Li3Br is a stronger halogen acceptor than the Cl atom in Li3Cl when it interacts with dihalogen molecules although their strength difference is small and the Li3I is the strongest Lewis base. To the best of our knowledge, this is the first report on halogen bonds involved with superatoms. The formation of halogen bonding has been analyzed with natural bond orbital (NBO), atoms in molecules (AIM), and energy decomposition. The results showed that the orbital interaction plays an important role for the stabilization of the complexes, which is different from conventional halogen bonds.

C–X⋯π halogen and C–H⋯π hydrogen bonding: interactions of CF3X (X = Cl, Br, I or H) with ethene and propene

Using FTIR and Raman spectroscopy, the formation of halogen bonded complexes of the trifluorohalomethanes CF(3)Cl, CF(3)Br and CF(3)I with ethene and propene dissolved in liquid argon has been investigated. For CF(3)Br and CF(3)I, evidence was found for the formation of C-X···π halogen bonded 1:1 complexes. At a higher ratio of CF(3)I/propene, weak absorptions due to a 2:1 complex were also observed. Using spectra recorded at different temperatures, the complexation enthalpies for the complexes were determined to be -5.3(2) kJ mol(-1) for CF(3)Br·ethene, -7.5(2) kJ mol(-1) for CF(3)I·ethene, -5.6(1) kJ mol(-1) for CF(3)Br·propene, -8.8(1) kJ mol(-1) for CF(3)I·propene and -16.5(6) kJ mol(-1) for (CF(3)I·)(2)propene. The complexation enthalpies of the hydrogen bonded counterparts, with CF(3)H as the Lewis acid, were determined to be -4.6(4) kJ mol(-1) for CF(3)H·ethene and -5.1(2) kJ mol(-1) for CF(3)H·propene. For both hydrogen bonded complexes, a blue shift, by +4.8 and +4.0 cm(-1), respectively, was observed for the C-H stretching mode. The results from the cryospectroscopic study are compared with ab initio calculations at the MP2/aug-cc-pVDZ(-PP) level.

A 19F NMR study of C–I⋯π halogen bonding

The formation of halogen bonded complexes between toluene-d 8 and the perfluoroiodopropanes 1-C 3F 7I and 2-C 3F 7I has been investigated using 19F NMR spectroscopy. For both Lewis acids, evidence was found for the formation of a C–I⋯π halogen bonded complex. The complex formed is a 1:1 type. Using spectra recorded at different temperatures, the complexation enthalpies and entropies for the complexes were determined to be −2.9(1) kJ mol −1 and −19.1(2) J K −1 mol −1 for the 2-C 3F 7I⋅toluene-d 8 complex and −2.7(1) kJ mol −1 and −16.0(4) K −1 mol −1 for the 1-C 3F 7I⋅toluene-d 8 complex. The experimental results are supported by ab initio calculations at the B3LYP-PCM/6-311++G(d,p) + LanL2DZ ∗ level.

Halogen bonding to a divalent sulfur atom: an experimental study of the interactions of CF3X (X = Cl, Br, I) with dimethyl sulfide

Using FTIR and Raman spectroscopy, the formation of halogen bonded complexes of the trifluorohalomethanes CF(3)Cl, CF(3)Br and CF(3)I with dimethyl sulfide (DMS) dissolved in liquid krypton has been investigated. For CF(3)Br and CF(3)I, evidence was found for the formation of C-XS halogen bonded 1:1 complexes. At higher concentrations of CF(3)I weak absorptions due to a 2:1 complex were also observed. Using spectra recorded at temperatures between 118 and 163 K, the complexation enthalpies for the complexes were determined to be -9.5(5) kJ mol(-1) for CF(3)Br·DMS, -17.4(1) kJ mol(-1) for CF(3)I·DMS and -30.8(16) kJ mol(-1) for (CF(3)I·)(2)DMS. The results from the cryospectroscopic study are compared with ab initio calculations at the MP2/aug-cc-pVDZ(-PP) level. Apart from vibrational modes localized in the trifluorohalomethanes and the DMS moieties, for both CF(3)Br and CF(3)I, an additional band, which we assign as the intermolecular stretching mode in the complex, was identified in the infrared and Raman spectra.

The C–Cl⋯N halogen bond, the weaker relative of the C–I and C–Br⋯N halogen bonds, finally characterized in solution

The formation of halogen bonded complexes between trimethylamine (TMA) and the trifluoro halomethanes CF 3I, CF 3Br and CF 3Cl dissolved in liquid xenon, krypton and argon, respectively, has been investigated using FTIR spectroscopy. For all Lewis acids, evidence was found for the formation of C–X⋯N halogen bonded 1:1 complexes. This study provides the first experimental characterization of a complex formed under thermodynamic equilibrium conditions in solution via a C–Cl⋯N halogen bond. Using spectra recorded at different temperatures, the complexation enthalpies for the complexes were determined to be −28.7(1) kJ mol −1 (CF 3I ·TMA), −18.3(1) kJ mol −1 (CF 3Br ·TMA) and −8.9(2) kJ mol −1 (CF 3Cl ·TMA). The results from the cryospectroscopic study are compared with ab initio calculations at the MP2/6-311++G(d,p) + LanL2DZ∗ level.

Directionality and site selectivity of N⋯Cl halogen bonding in two azaaromatic chloride crystals

Two azaaromatic chlorides of bis-2,4-[(2-formoyl)phenoxyl]-6-chloro-[1,3,5]triazine ( 1) and bis-2,4-(4-carbomethoxyphenoxyl)-6-chloro-[1,3,5]triazine ( 2) have been synthesized and structurally characterized. The crystal structures of 1 and 2 reveal unusually short intermolecular N⋯Cl distance of 3.095(2) and 3.088(3) Å, meaning the formation of strong halogen bonding. The strengths of the intermolecular N⋯Cl halogen bonding and the molecular electrostatic potentials in these crystal structures have been calculated by Density Functional Theory Calculations. The capacities of the N⋯Cl halogen bonding, lone pair⋯π interaction, π–π stack and C−H⋯O hydrogen bonding in the directionality of supramolecular self-assembly have been analyzed by structural study and theoretical calculations. The site selectivity of the N⋯Cl halogen bonding is illustrated by the difference of electrostatic potential of the N atoms on the molecule.

Halogen⋯oxygen aggregation and disorder modes in pressure frozen XCF2CF2X : 1,4-dioxane (X = Br,I) complexes

Formation of cocrystals and halogen⋯O interactions was studied in the structures of 1,4-dioxane with 1,2-diiodo-, 1-bromo-2-iodo- and 1,2-dibromoperfluoroethanes. Mixtures pressure-frozen in a diamond-anvil cell have been investigated. Structures of cocrystals of 1,2-diiodoperfluoroethane : 1,4-dioxane at 0.30(5) GPa/296(2) K and of 1-bromo-2-iodoperfluoroethane : 1,4-dioxane at 0.62(5) GPa/296 K were determined by single-crystal X-ray diffraction. Also the single-crystal of 1,4-dioxane separated from its mixture with 1,2-dibromoperfluoroethane, which remained liquid, was investigated at 0.42 GPa/296 K. The cocrystal of ICF2CF2I : C4H8O2 and the C4H8O2 crystals freeze into the same phases as those obtained by cooling; the BrCF2CF2I : C4H8O2 cocrystal was not synthesized before. In all these cocrystals the structures are dominated by halogen⋯O interactions. In the structure of ICF2CF2I : C4H8O2 the –CF2–CF2– moiety is disordered about the I⋯I molecular axis and the C4H8O2 molecule rotates about the O⋯O axis, too; in BrCF2CF2I : C4H8O2 the Br and I atoms are disordered at the same position with half occupancy, but the C4H8O2 molecule is ordered. The pressure-freezing of 1,4-dioxane from the BrCF2CF2Br : C4H8O2 mixture yielded ordered phase II of 1,4-dioxane previously obtained from the neat compound by cooling. Spectacular kinetic crystallization of ICF2CF2I : C4H8O2 in the form of hexagonal snowflakes has been observed in the diamond-anvil cell.

Halogen-Bonded Supramolecular Assemblies Based on Phenylethynyl Pyridine Derivatives: Driving Crystal Packing through Systematic Chemical Modifications

A series of phenylethynyl pyridine derivatives 1−4 possessing both perfluorocarbon (PFC) and hydrocarbon (HC) moieties have been synthesized and used for the formation of halogen bonding (XB)-based networks. X-ray crystal structure analyses indicate the dominance of XB synthons, which represent the one-dimensional (1D) structure directing interaction, leading to the formation of supramolecular chains. The influence of structural/electronic factors (e.g., electron donor/acceptor strength, sterically demanding substituents) on XB formation of compounds 1−4 have been compared with structurally related stilbazole systems (I, II). The XB-bonded networks are formed in collaboration with other noncovalent interactions such as π−π stacking, hydrogen bonding, C−H···F and F···F. Molecular electrostatic potentials and atomic polar tensor (APT) charges of the donor and acceptor sites have been determined by density functional theory (DFT) calculations.

Comparison of disinfection byproduct formation from chlorine and alternative disinfectants

Seven diverse natural waters were collected and treated in the laboratory under five oxidation scenarios (chlorine, chloramine, both with and without preozonation, and chlorine dioxide). The impact of these disinfectants on the formation of disinfection byproducts was investigated. Results showed that preozonation decreased the formation of trihalomethanes (THMs), haloacetic acids (HAAs) and total organic halogen (TOX) for most waters during postchlorination. A net increase in THMs, HAAs and TOX was observed for a water of low humic content. Either decreases or increases were observed in dihaloacetic acids and unknown TOX (UTOX) as a result of preozonation when used with chloramination. Chloramines and chlorine dioxide produced a higher percentage of UTOX than free chlorine. They also formed more iodoform and total organic iodine (TOI) than free chlorine in the presence of iodide. Free chlorine produced a much higher level of total organic chlorine (TOCl) and bromine (TOBr) than chloramines and chlorine dioxide in the presence of bromide.

Processing Aryllithium and Hetaryllithium Intermediates: Formation of Halogen and Chalcogen Derivatives.

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