Interplay between halogen bonds and hydrogen bonds in OH/SH···HOX···HY (X = Cl, Br; Y = F, Cl, Br) complexes

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 _S,min) and the most positive electrostatic potentials (V _S,max) on the electron density contours of the individual species. The greater the V _S,max 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 _S,max 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.

Theoretical investigations of the H···π and X (X = F,Cl, Br,I)···π complexes between hypohalous acids and benzene

The H···π and X (X = F, Cl, Br, I)···π interactions between hypohalous acids and benzene are investigated at the MP2/6-311++G(2d,2p) level. Four hydrogen-bonded and three halogen-bonded complexes were obtained. Ab initio calculations indicate that the X···π interaction between HOX and C₆H₆ is mainly electrostatically driven, and there is nearly an equal contribution from both electrostatic and dispersive energies in the case of XOH–C₆H₆ complexes. Natural bond orbital (NBO) analysis reveals that there exists charge transfer from benzene to hypohalous acids. Atom in molecules (AIM) analysis locates bond critical points (BCP) linking the hydrogen or halogen atom and carbon atom in benzene.     

The cooperativity between hydrogen and halogen bond in the XY···HNC···XY (X,Y = F,Cl, Br) complexes

The cooperativity between hydrogen and halogen bonds in XY···HNC···XY (X, Y = F, Cl, Br) complexes was studied at the MP2/aug-cc-pVTZ level. Two hydrogen-bonded dimers, five hydrogen-bonded dimers, and ten trimers were obtained. The hydrogen- and halogen-bonded interaction energies in the trimers were larger than those in the dimers, indicating that both the hydrogen bonding interaction and the halogen bonding interaction are enhanced. The binary halogen bonding interaction plays the most important role in the ternary system. The hydrogen donor molecule influences the magnitude of the halogen bonding interaction much more than the hydrogen bonding interaction in the trimers with respect to the dimers. Our calculations are consistent with the conclusion that the stronger noncovalent interaction has a bigger effect on the weaker one. The variation in the vibrational frequency in the HNC molecule was considered. The NH antisymmetry vibration frequency has a blue shift, whereas the symmetry vibration frequency has a red shift. A dipole moment enhancement is observed upon formation of the trimers. The variation in topological properties at bond critical points was obtained using the atoms in molecules method, and was consistent with the results of the interaction energy analysis.     

The competition of C-X⋯O=P halogen bond and π-hole⋯O=P bond between halopentafluorobenzenes C6F5X (X=F, Cl, Br, I) and triethylphosphine oxide

Calculation predicted the interacting forms of halopentafluorobenzene C₆F₅X (X=F, Cl, Br, I) with triethylphosphine oxide which is biologically interested and easily detected by ³¹P NMR. The interaction energy and geometric parameters of resultant halogen or π-hole bonding complexes were estimated and compared. Moreover, the bonding constants were determined by ³¹P NMR. Both theory and experiments indicated the C₆F₆ and C₆F₅Cl interact with triethylphosphine oxide by π-hole bonding pattern, while C₆F₅I by halogen/σ-hole bonding form. For C₆F₅Br, two interactions are comparative and should coexist competitively. The calculated interaction energies of σ-hole bonding complexes, ?5.07 kcal mol^?1 for C₆F₅Br?O=P and ?8.25 kcal mol^?1 for C₆F₅I?O=P, and π-hole bonding complexes, ?7.29 kcal mol^?1 for C₆F₆?O=P and ?7.24 kcal mol^?1 for C₆F₅Cl?O=P, are consistent with the changing tendency of bonding constants measured by ³¹P NMR, 4.37, 19.7, 2.42 and 2.23 M^?1, respectively.

Theoretical potential scans and vibrational spectra of vinyl selenonyl halides CH2=CH–SeO2X (X is F, Cl and Br)

The structure and conformational stability of vinyl selenonyl fluoride, chloride and bromide CH₂=CH–SeO₂X (X is F, Cl and Br) were investigated using density functional B3LYP/6-311+G** and ab initio MP2/6-311+G** calculations. From the calculations the molecules were predicted to exist only in the non-planar gauche conformation with the vinyl C=C group almost eclipsing one of the selenonyl Se=O bonds as a result of conjugation between the two moieties. Single-minimum potential scans were calculated at the DFT level for the molecules. The vibrational frequencies were computed using B3LYP/6-311+G**. Normal coordinate calculations were then carried out and potential energy distributions were calculated for the three molecules in the gauche conformation.Figure Potential function for the asymmetric torsion in vinyl selenonyl fluoride (dotted line), chloride (dashed line) and bromide (solid line) as determined at the DFT-B3LYP/6-311+G** level     

Natural bond orbital, nuclear magnetic resonance analysis and hybrid-density functional theory study of σ-aromaticity in Al2F6, Al2Cl6, Al2Br6 and Al2I6

Natural bond orbital (NBO), nuclear magnetic resonance (NMR) analysis and hybrid-density functional theory based method (B3LYP/Def2-TZVPP) were used to investigate the correlation between the nucleus-independent chemical shifts [NICS, as an aromaticity criterion], σ _Al(1)-X2(b) → σ*_Al(3)-X4(b) electron delocalizations and the dissociation energies of Al₂F₆, Al₂Cl₆, Al₂Br₆ and Al₂I₆ to 2AlX₃ (X?=?F, Cl, Br, I). The results obtained showed that the dissociation energies of Al₂F₆, Al₂Cl₆, Al₂Br₆ and Al₂I₆ decrease from Al₂F₆ to Al₂I₆. Like aromatic molecules, these compounds have relatively significant negative NICS_iso(0) values. Clearly, based on magnetic criteria, they exhibit aromatic character and make it possible to consider them as σ-delocalized aromatic species, such as Möbius σ-aromatic species. The σ-aromatic character which is demonstrated by their NICS_iso(0) values decreases from Al₂F₆ to Al₂I₆. The NICS_iso values are dominated by the in-plane σ₂₂ (i.e., σ_yy, the plane containing halogen atoms bridged) chemical shift components. The increase of the NICS_iso values explains significantly the decrease of the corresponding dissociation energies of Al₂F₆, Al₂Cl₆, Al₂Br₆ and Al₂I₆. Importantly, the NBO results suggest that in these compounds the dissociation energies are controlled by the stabilization energies associated with σ _Al(1)-X2(b) →σ*_Al(3)-X4(b) electron delocalizations. The decrease of the stabilization energies associated with σ _Al(1)-X2(b) →σ*_Al(3)-X4(b) electron delocalizations is in accordance with the variation of the calculated NICS_iso values. The correlations between the dissociation energies of Al₂F₆, Al₂Cl₆, Al₂Br₆ and Al₂I₆, σ _Al(1)-X2(b) →σ*_Al(3)-X4(b) electron delocalizations, natural atomic orbitals (NAOs) and NICS_iso values have been investigated.     

Conformational stability and normal coordinate analyses for 1-halovinyl azides CH<Subscript>2</Subscript>=CX–NNN (X is F,Cl and Br)

The conformational behavior of 1-halovinyl azides CH2=CX-NNN (X=F, Cl and Br) were investigated by DFT-B3LYP and ab initio MP2 calculations with the 6-311++G** basis set. The molecules were predicted to exist predominantly in the trans (the vinyl CH2=CH- and the azide -NNN groups are trans to each other) conformation. The relative energy between cis and trans were calculated to decrease in order: bromide>chloride>fluoride. Full optimization was performed at the ground and transition states in the molecule at both MP2 and B3LYP levels. The barrier to internal rotation around the C-N single bond in the three molecules was calculated to be about 4-5 kcal mol(-1). The vibrational frequencies were computed at the DFT-B3LYP level and the calculated infrared and Raman spectra of the cis- trans mixture of the three molecules were plotted. Complete vibrational assignments were made on the basis of normal coordinate calculations for both stable conformers of the three molecules.     

Theoretical study on cooperative effects between X⋯N and X⋯Carbene halogen bonds (X = F,Cl,Br and I)

Quantum chemical calculations are performed to study the interplay between halogen?nitrogen and halogen?carbene interactions in NCX?NCX?CH₂ complexes, where X?=?F, Cl, Br and I. Molecular geometries and interaction energies of dyads and triads are investigated at the MP2/aug-cc-pVTZ level of theory. It is found that the X?N and X?C_carbene interaction energies in the triads are larger than those in the dyads, indicating that both the halogen bonding interactions are enhanced. The estimated values of cooperative energy E _coop are all negative with much larger E _coop in absolute value for the systems including iodine. The nature of halogen bond interactions of the complexes is analyzed using parameters derived from the quantum theory atoms in molecules methodology and energy decomposition analysis.

Theoretical study of noncovalent interactions in XCN···YO<Subscript>2</Subscript>H (X = F,Cl, Br,I; Y = P,As, Sb) complexes

Noncovalent interactions in XCN···YO₂H (X = F, Cl, Br, I; Y = P, As, Sb) complexes were investigated using ab initio calculations at the MP2/aug-cc-pVDZ level of theory. There are four different configurations of these complexes, and the complexes are formed via hydrogen bonds, halogen bonds, π-hole interactions, or dual interactions. An examination of binding distances and interaction energies suggested that π-hole bonds are more stable than the other interactions. Molecular electrostatic potentials, electron densities, second-order stabilization energies, and electron density differences were computed to study the character of these interactions.     

The reactivity of bromoform with [Au(CH2)2PPh2]2. The completion of the halomethane series CHyX4−y (y=3,2,1,0; X=Cl,Br, I) and reactivity with [Au(CH2)2PPh2]2

The reaction of [Au(CH₂)₂PPh₂]₂ with excess CHBr₃ in benzene initially gives [Au(CH₂)₂PPh₂]₂₋ (CHBr₂)Br. This observation establishes that halomethanes, CH_yX_4−y (y=3,2,1,0; X=Cl, Br, I), react with [Au(CH₂)₂PPh₂]₂ to initially give Au(II) adducts of the general form [Au(CH₂)₂PPh₂]₂₋(CH_yX_3−y)X (y=3,2,1,0) via oxidative addition across the carbon-halogen bond. The order of reactivity inversely follows the order of carbon-halogen bond dissociation energies of haloalkanes. Methyl chloride is the only halomethane of the series that does not give a Au(II) adduct under similar reaction conditions.     

Reactions of VCl3, VCl4 and TiX4 (XCl,Br) with benzofuroxan and its 5-methyl-, 5-chloro- and 5-methoxi-derivatives. I.

By means of the reaction between VCl₃ and benzofuroxan the compound VCl₃·2C₆H₄N₂O₂ was obtained, while in reaction with TiX₄ (XCl, Br) the compounds with stoichiometry TiX₄·C₆H₄N₂O₂ (X Cl, Br) were obtained.Furthermore, with some benzofuroxan derivatives (5-methyl, 5-chloro and 5-methoxi) the complexes MCl₄·2YC₆H₃N₂O₂ (MTi, V; YCH₃O, Cl, CH₃), TiCl₄·YC₆H₃N₂O₂ (YCH₃O, CH₃) and TiBr₄·YC₆H₃N₂O₂ (YCH₃O, Cl, CH₃) have been isolated.The compounds were characterized by elementary analysis, cryoscopic molecular weight determination in nitrobenzene, magnetic measurements and IR, Vis and EPR spectroscopy.     

Synthesis, structure, and formation mechanism of the halogen-bridged tricobalt clusters, [Co3Cp3(μ3-CPh)2(μ-X)] (X=Cl, Br, and I)

Reactions of a benzylidyne-capped tricobalt cluster, [Co₃Cp₃(μ₃-CPh)₂] (1), with halogens (X₂ = Cl₂, Br₂, and I₂) in CH₂Cl₂ afforded halogen-adducts of 1. The structure of four isolated salts [Co₃Cp₃(μ₃-CPh)₂(μ-Cl)]PF₆ · MeCN (2PF₆ · MeCN), [Co₃Cp₃(μ₃-CPh)₂(μ-Br)]SbF₆ (3SbF₆), [Co₃Cp₃(μ₃-CPh)₂(μ-I)]SbF₆ · CH₂Cl₂ (4SbF₆ · CH₂Cl₂), and [Co₃Cp₃(μ₃-CPh)₂(μ-I)]I₃ (4I₃) determined by X-ray diffraction can be regarded formally as halide-adducts of 1²⁺. The halogen atom in each structure lies in the Co₃ plane. The halogen-bridged Co-Co edge was elongated (in 2PF₆ · MeCN = 2.6072(4), in 3SbF₆ = 2.6106(7), in 4SbF₆ · CH₂Cl₂ = 2.622(2), and in 4I₃=2.6718(9) Å), and the Co-Co distances that had no halogen-bridge remained unchanged from the Co-Co distance of 1 (2.382(8) Å), (in 2PF₆=2.4037(8) and 2.3948(7), in 3SbF₆=2.3888(6) and 2.4017(7), in 4SbF₆ · CH₂Cl₂ = 2.393(2) and 2.388(1), and in 4I₃ = 2.397(1) and 2.3868(9) Å). The UV-Vis absorption spectra of 2⁺, 3⁺, and 4⁺ had characteristic absorption peaks at 796, 819, and 844 nm, respectively. Cyclic voltammograms of 2PF₆ in CH₂Cl₂ with 0.1 M ⁿBu₄NPF₆ as the supporting electrolyte showed a chemically reversible oxidation (at a potential of 0.75 V versus Fc/Fc⁺), and an irreversible reduction wave at −0.57 V. The irreversible reduction resulted in the recovery of 1. The redox properties of 3⁺ and 4⁺ are very similar to that of 2⁺. Cyclic voltammetry of 1 in 0.1 M ⁿBu₄NCl/MeCN indicates that the formation of 2⁺ is a multi-step reaction. Initially, 1 is oxidized to 1⁺, and then, 1⁺ is coordinated by Cl⁻ followed by immediate oxidation to 2⁺.     

Stoichiometry and products of transmetalation of dimeric copper(I) complexes L2Cu2X2 (L is an N,N,N′,N′-tetraalkylethylenediamine; X = Cl or Br) by M(NS)2 reagents in aprotic solvents

Dimeric copper(I) complexes L₂Cu₂X₂ react with 1 and 2 mol of M(NS)₂ reagents in aprotic solvents to give quantitative yields of products LMX₂ and (NS)M(X,X)M(NS), respectively. Here, L = N,N,N′N′-tetraethylethylenediamine, X = Cl or Br, M = Co, Ni, Cu and Ns = S-methylisopropylidenehydrazinecarbodithioate. Dimers (NS)Cu(X,X)Cu(NS) are oxidatively unstable. LCoCl₂ crystallizes in the monoclinic space group P2₁/c (C_2h⁵): a = 7.345(1), b = 11.801(1), c = 17.478(2) Å, β = 104.98(1)°, Z = 4. The electronic spectra of LMX₂ and (NS)M(X,X)M(NS) complexes are discussed.     

Synthesis and characterization of triaminecobalt(III) complexes and acid hydrolysis kinetics of fac-[Codpt(H2O)nX3−n]n+ (X = Cl,Br; n = 0,1,2)

The complexes CodptX₃ and [Codpt(H₂O)X₂]ClO₄ (X = Cl, Br; dpt = dipropylenetriamine = NH(CH₂CH₂CH₂NH₂)₂) have been prepared and characterized. Rate constants (s⁻¹) for aqueous solution at 25 °C and μ = 0.5 M (NaClO₄), for the acid-independent sequential ractions.

have been measured spectrophotometrically. For X = Cl: k₁ ⋍ 2 × 10⁻², k₂ = 1.7 × 10⁻⁴ and k₃ = 4.8 × 10⁻⁶, and for X = Br: k₁ ⋍ 2 × 10⁻², k₂ = 5.25 × 10⁻⁴ and k₃ = 2.5 × 10⁻⁵ The primary equation was found to be acid independent, while the secondary and tertiary aquations were acid-inhibited reactions. For the second step, the rate of the reaction was given by the rate equation

where C_t is the complex concentration in the aqua-and hydroxodihalo species, k′₂ is the rate constant for the acid-dependent pathway and K_a is the equilibrium constant between the hydroxo and aqua complex ions. The activation parameters were evaluated, for X = Cl: ΔH^≠₂ = 106.3 ± 0.4 kJ mol⁻¹ and ΔS^≠₂ = 40.2 ± 1.7 J K⁻¹ mol⁻, and for X = Br: ΔH^≠₂ = 91.6 ± 0.4 kJ mol⁻¹ and ΔS^≠₂ = 0.4 ± 1.7 J K⁻¹ mol⁻¹. The results are discussed and detailed comparisons of the reactivities of these complexes with other haloaminecobalt(III) species are presented.     

Comparison of the directionality of the halogen,hydrogen, and lithium bonds between HOOOH and XF (X = Cl,Br, H,Li)

Detailed electrostatic potential (ESP) analyses were performed to compare the directionality of halogen bonds with those of hydrogen bonds and lithium bonds. To do this, the interactions of HOOOH with the molecules XF (X?=?Cl, Br, H, Li) were investigated. For each molecule, the percentage of the van der Waals (vdW) molecular surface that intersected with the ESP surface was used to roughly quantify the directionality of the halogen/hydrogen/lithium bond associated with the molecule. The size of the region of intersection was found to increase in the following order: ClF?<?BrF?<?HF?<?LiF. The maximum ESP in the region of intersection, V _{S, max}, was observed to become more positive according to the sequence ClF?<?BrF?<?HF?<?LiF. For ClF and BrF, the positive electrostatic potential was concentrated in a very small region of the vdW molecular surface. On the other hand, for HF and LiF, the positive electrostatic potential was more diffusely scattered across the vdW surface than for ClF and BrF. Also, the optimized geometries of the dipolymers HOOOH···?XF (X?=?Cl, Br, H, Li) indicated that halogen bonds are more directional than hydrogen bonds and lithium bonds, consistent with the results of ESP analyses.

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Graphical abstract Electrostatic potential (ESP) contour maps in the xz plane of ClF and BrF

     

Structures and aromaticity of X2Y 2 − (X = C, Si, Ge and Y = N, P, As) anions

The equilibrium geometries, total energies, and vibrational frequencies of anions X₂Y₂ ⁻ (X = C, Si, Ge and Y = N, P, As) are theoretically investigated with density functional theory (DFT) method. Our calculation shows that for C₂N₂ ⁻ species, the D _2h isomer is the most stable four-membered structure, and for other species the C _2v isomer in which two X atoms are contrapuntal is the most stable structure at the B3LYP/6-311 +G_* level. Wiberg bond index (WBI) and negative nucleus-independent chemical shift (NICS) value indicate the existence of delocalization in stable X₂Y₂ ⁻ structures. A detailed molecular orbital (MO) analysis further reveals that stable isomers of these species have strongly aromatic character, which strengthens the structural stability and makes them closely connected with the concept of aromaticity.     

Crystal structure and properties of [TTF]2.5[V(mnt)3 ]·0.5CH2ClCH2Cl[TTF = tetrathiafulvalene and mnt = 1,2-dicyanoethylene-1,2-dithiolate(2−)]

The title salt was obtained by a reaction of [TTF]₃ [BF₄]₂ (TTF = tetrathiafulvalene) with [NMe₄]₂ [V(mnt)₃] [mnt = 1,2-dicyanoethylene-1,2- dithiolate(2−)] in a mixture of 1,2-dichloroethane and acetonitrile (3:2 ν/ν). A single crystal X-ray analysis of it revealed a TTF columnar structure consisting of both TTF⁰ and the TTF^·+ radical cation and the distorted octahedral geometry of the [V(mnt)₃]²⁻ anion. The salt crystallizes in a monoclinic system, space group C2/c with unit cell constants a = 25.428(3), b = 12.434(2), c = 25.477(3) Å, β = 92.428(3)° and Z = 8. The structure was solved by the direct method and refined, on the basis of 3854 [|F_o| > 3σ(F)] observed data, to an R value of 0.078. The salt e`xhibits electrical conductivity of 1.7 x 10⁻⁴ S cm⁻¹ at 25°C for a compacted pellet.