Theoretical calculations focusing on the cleavage of the C–X bond in methyl halides (CH3X; X?=?Cl, Br, I) as mediated by CoI-based systems have been carried out using the hybrid functional ωB97-XD together with the basis set 6–311++G(2d,2p). A total of seven CoI-based compounds were evaluated: cob[I]alamin (CoICbl) in its base-on form and cobaloxime (CoICbx) with either no ligand or different ligands (either pyridine (PYR), tributylphosphine (TBP), dimethyl sulfide (DMS), cyclohexylisocyanide (CI), or 5,6-dimethylbenzimidazole (DMB)) at the lower axial position. For the large CoICbl system, an ONIOM scheme was employed, where the high layer was described at the DFT level and the low layer was computed using the semi-empirical method PM6. A full DFT model was employed for the CoICbx cases. An SN2-like mechanism was evaluated in all cases. The intrinsic reaction coordinate profiles suggested early transition states with activation energies of ≈ 12 kcal/mol, ≈ 10 kcal/mol, and ≈ 5 kcal/mol for C–Cl, C–Br, and C–I cleavage, respectively, which is consistent with the leaving group abilities of these halides. The evolutions of the atomic charges in and the bond orders of Co–C and C–X were computed, and the results confirmed the existence of early transition states (δBav≈ 40%), where the polarization Cδ+–Xδ? (%Ev?≈?43%) is the determining factor in the reaction process. Finally, a comparison of all the determined parameters showed that the reaction in the DMB–CoICbx system resembles the process that occurs in the larger CoICbl, suggesting that the former system could be a reliable model for the study of reductive dehalogenation mediated by vitamin B12, which is key to the anaerobic microbiological treatment of halocarbon contaminants. 相似文献
This paper presents a theoretical study of the effects of substituents (F, Cl, Br, CH3, and CN) on the aromaticity of borazine (B3N3H6), using density functional theory (DFT) and the Hartree-Fock (HF) method. The calculations to optimize the geometries, structural properties, and vibrational frequencies were performed using the same 6–311G(d,p) and 6–311++G(d,p) basis sets, comparing the methods with experimental results. In the analysis of the NICSZZ values, it was found that that replacing the hydrogen atoms by halogen atoms (F, Cl, and Br) and CH3 reduced the aromaticity of the borazine molecule, while use of the CN group resulted in NICSZZ values (0.9–2.0 Å) very close to those of borazine, presenting the following order of increasing aromaticity: B3N3H3-(Br)3?<?B3N3H3-(Cl)3?<?B3N3H3-(F)3?<?B3N3H3-(CH3)3?<?B3N3H6 ~ B3N3H3-(CN)3. All the spectra of the compounds showed only the presence of transition peaks distant from the UV region, reflecting the large energy difference between the HOMO and LUMO orbitals. After the substitution of the borazine ring, all the compounds presented an intensification of the spectrum, with a shift of the maximum absorbance toward red, indicative of a bathochromic effect. There was a direct inverse relation between the energy gap and the maximum wavelength of the compounds. 相似文献
Adsorption of three alkaline earth cations inside and outside of a B12N12 nano-cage in aqueous medium was investigated using density functional theory. The results obtained are discussed in terms of thermodynamic, geometric, and electronic properties. Based on the calculation of enthalpy changes at 298 K and 1 atm, the adsorption of the considered cations was found to be exothermic outside the cluster while it is endothermic inside. It was also found that the exohedral adsorption favorability of the cluster increases in the series: Ca2+?<?Mg2+?<<?Be2+ with Gibbs free energy changes in the range of ?0.08 to ?1.53 eV at B3LYP/6-31G (d) level of theory. Overall, interaction of the cations with the cluster influences the electronic properties of the cluster through stabilizing the HOMO and LUMO as well as reducing the energy gap between them. However, the electronic properties changed much more in the case of endohedral adsorption in comparison with the exohedral adsorption. 相似文献
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?Ccarbene 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 Ecoop are all negative with much larger Ecoop 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.
Figure
The structure of NCX?NCX?CH2 complexes (X?=?F, Cl, Br and I) 相似文献
The structural, optical and magnetic properties of Cu, Ag, Au-doped Si7 Clusters have been systematically investigated using density functional theory calculations. The global optimized structures of Cu, Ag, Au-doped Si clusters are predicted to have a lower HOMO–LUMO gap and higher magnetic moment. M-doping (M?=?Cu, Ag, Au) in Si cluster widens a range of adsorption wavelength, especially Au-doping. The characteristics in electronic density of states (DOSs) show that C5v-Si6Cu has a big asymmetrical spin-up and spin-down. The average atomic moment is 0.428 mμB per atom for the Si6Cu cluster with C5v symmetry, while the average paramagnetic moment is 0.143 mμB per atom for other M-doped (M?=?Cu, Ag, Au) Si7 clusters. 相似文献
Halogen-bonding, a noncovalent interaction between a halogen atom X in one molecule and a negative site in another, plays critical roles in fields as diverse as molecular biology, drug design and material engineering. In this work, we have examined the strength and origin of halogen bonds between carbene CH2 and XCCY molecules, where X?=?Cl, Br, I, and Y?=?H, F, COF, COOH, CF3, NO2, CN, NH2, CH3, OH. These calculations have been carried out using M06-2X, MP2 and CCSD(T) methods, through analyses of surface electrostatic potentials VS(r) and intermolecular interaction energies. Not surprisingly, the strength of the halogen bonds in the CH2···XCCY complexes depend on the polarizability of the halogen X and the electron-withdrawing power of the Y group. It is revealed that for a given carbene···X interaction, the electrostatic term is slightly larger (i.e., more negative) than the dispersion term. Comparing the data for the chlorine, bromine and iodine substituted CH2···XCCY systems, it can be seen that both the polarization and dispersion components of the interaction energy increase with increasing halogen size. One can see that increasing the size and positive nature of a halogen’s σ-hole markedly enhances the electrostatic contribution of the halogen-bonding interaction.
Graphical abstract
Halogen bonding interactions between carbene and X-CC-Y molecules (X?=?Cl, Br, and I; Y?=?H, F, COF, COOH, CF3, NO2, CN, OH, NH2, CH3) 相似文献
Quantum chemical calculations have been performed for the complexes Li3OCCX–Y (X?=?Cl, Br, H; Y?=?NH3, H2O, H2S) and Li3OCN–X′Y′ (X′Y′?=?ClF, BrCl, BrF, HF) to study the role of superalkalis in hydrogen and halogen bonds. The results show that the presence of an Li3O cluster in a Lewis acid weakens its acidity, while its presence in a Lewis base enhances its basicity. Furthermore, the latter effect is more prominent than the former one, and the presence of an Na3O cluster causes an even greater effect than Li3O. The strengths of hydrogen and halogen bonds were analyzed using molecular electrostatic potentials. The contributions of superalkalis to the strength of hydrogen and halogen bonds were elucidated by analyzing differences in electron density. 相似文献
A combined density functional and ab initio quantum chemical study of the insertion reactions of the germylenoid H2GeLiF with SiH3X (X?=?F, Cl, Br) was carried out. The geometries of all the stationary points of the reactions were optimized using the DFT B3LYP method and then the QCISD method was used to calculate the single-point energies. The theoretical calculations indicated that along the potential energy surface, there were one precursor complex (Q), one transition state (TS), and one intermediate (IM) which connected the reactants and the products. The calculated barrier heights relative to the respective precursors are 102.26 (X?=?F), 95.28 (X?=?Cl), and 84.42 (X?=?Br) kJ mol-1 for the three different insertion reactions, respectively, indicating the insertion reactions should occur easily according to the following order: SiH3-Br?>?SiH3-Cl?>?SiH3-F under the same situation. The solvent effects on the insertion reactions were also calculated and it was found that the larger the dielectric constant, the easier the insertion reactions. The elucidations of the mechanism of these insertion reactions provided a new reaction model of germanium-silicon bond formation. 相似文献
The character of the bridged hydrogen atom (Hb) of B2H6 has become a hot issue in recent years. In this work, the complexes B2H6?·?·?·?NH3, B2H2X4?·?·?·?nNH3 (n?=?1, 2) and 2HF?·?·?·?B2H2X4?·?·?·?2NH3 (X?=?Cl, Br, I) were constructed and studied based on the M06-2X calculations to investigate how to enhance the Hb?·?·?·?N hydrogen-bonded interaction. When the terminal hydrogen atoms (Ht) of B2H6 were replaced by X (X?=?Cl, Br, I) atoms, the Hb?·?·?·?N hydrogen bond were strengthened. According to the electrostatic potentials in B2H2X4, two HF molecules were added to the interspace of the B-H-B-H four-membered ring of the B2H2X4?·?·?·?2NH3 complexes, and H?·?·?·?X hydrogen bond formed, resulting in further enhancing effect of Hb?·?·?·?N hydrogen bond. As a result, the positive cooperative effect of Hb?·?·?·?N hydrogen bond and H?·?·?·?X hydrogen bond do enhance the interactions of each other. The two measures not only enhance the strength of Hb?·?·?·?N hydrogen bond, but also achieve the goal to make the Hb?·?·?·?N hydrogen bond perpendicular to B?·?·?·?B direction.
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.
Figure
The competitive σ-hole···O=P and π-hole···O=P bonds between C6F5X (X=F, Cl, Br, I) and O=PEt3相似文献
Chemical functionalization of a single-walled carbon nanotube (CNT) with different carboxylic derivatives including –COOX (X?=?H, CH3, CH2NH2, CH3Ph, CH2NO2, and CH2CN) has been theoretically investigated in terms of geometric, energetic, and electronic properties. Reaction energies have been calculated to be in the range of ?0.23 to ?7.07 eV. The results reveal that the reaction energy is increased by increasing the electron withdrawing character of the functional groups so that the relative magnitude order is ?CH2NO2?>?CH2CN?>?H?>?CH2Ph?>?CH3?>?CH2NH2. The chemical functionalization leads to an increase in HOMO/LUMO energy gap of CNT by about 0.32 to 0.35 eV (except for ?H). LUMO, HOMO, and Fermi level of the CNT are shifted to lower energies especially in the case of ?CH2NO2 and ?CH2CN functional groups. Therefore, it leads to an increment in work function of the tube, impeding the field electron emission. 相似文献
We present a systematic investigation of the nature and strength of the hydrogen bonding in HX···HX and CH3X…HX (X = Br, Cl and F) dimers using ab initio MP2/aug-cc-pVTZ calculations in the framework of the quantum theory of atoms in molecules (QTAIM) and electron localisation functions (ELFs) methods. The electron density of the complexes has been characterised, and the hydrogen bonding energy, as well as the QTAIM and ELF parameters, is consistent, providing deep insight into the origin of the hydrogen bonding in these complexes. It was found that in both linear and angular HX…HX and CH3X…HX dimers, F atoms form stronger HB than Br and Cl, but they need short (~2 Å) X…HX contacts. 相似文献
A series of monomeric tetrahedral complexes of stoichiometry, [MX(HL)(Ph3P)2] (In case of M = Cu, H1L, X = I, 1; Br, 2; Cl, 3; H3L, X = I, 4; Br, 5; Cl, 6; H4L, X = I, 7; Br, 8; Cl, 9 and in case of M = Ag, H1L, X = Cl, 13; Br, 14; H2L, X = Cl, 15, Br 16; H3L, X = Cl, 17, Br, 18) were synthesized by the reaction of copper (I) or silver (I) halides with indole-3-thiosemicarbazone (H1L) or 5-methoxy indole-3-thiosemicarbazone (H2L) or 5-methoxy indole-N1-methyl-3-thiosemicarbazone (H3L), whereas dimers of stoichiometry, [Cu2(μ-X)2(η1-S-H2L)2(Ph3P)2] (X = I, 10; Br, 11; Cl, 12) were obtained by the reaction of copper (I) halides with indole-N1-methyl-3-thiosemicarbazone (HIntsc-N1-Me, H2L). The synthesized complexes were characterized using NMR (1H and 13C) and single crystal X-ray diffraction (H2L, 3, 7, 8, 10, 11 and 13) as well as elemental analysis. Anti- M. tuberculosis activity of ligands (H1L-H4L) and their metal complexes (1–18) were evaluated against M. tuberculosis H37RV strain ATCC 27294. It has been observed that there is unusual enhancement in anti TB activity of these ligands on complexation with copper (I) and silver (I). Molecular modelling studies in the active binding site are also giving complementary theoretical support for the experimental biological data acquired. 相似文献
The structures of solvated methylmercury(II) halides in pyridine solution were determined by a large angle X-ray scattering technique. Near-linear CH3HgX (X = Cl, Br and I) species solvated by two weakly-coordinated pyridine molecules are indirectly interpreted. Additional mercury-pyridine interactions, through van der Waals forces, are found at the sum of the van der Waals radii. The HgX bond distances in the methylmercury(II) halides are found to be 2.325(8), 2.480(3) and 2.649(3) Å for chloride, bromide and iodide, respectively. The HgC bond distances are assumed to be ∼2.08 Å. This interaction is indicated in the radial distribution functions. The bond distance between mercury and the two solvating pyridine molecules is ∼2.8 Å, e.g., 2.84(2) Å in methylmercury(II) bromide. The additional mercury interactions with roughly two pyridine molecules at the sum of van der Waals radii are revealed at around 3.15 Å. Comparison between Raman stretching vibrations and the solvated structures of methylmercury(II) complexes found in various solvents indicates a lower limit in solvent donor property for the formation of solvate bonds to mercury for the methylmercury(II) halides. 相似文献
Treatment of [(iPrNH2)B8H11NHiPr] with elemental halogen affords the 8-exo-halogen-substituted derivatives [(iPrNH2)B8H10XNHiPr] (X=Cl, Br, I). The structures of all three compounds are confirmed by NMR spectroscopy and mass spectrometry, and (for X=Br) by an X-ray diffraction study. The bromoazanonaborane undergoes hydrolytic decomposition to the new five-vertex compound [B5H10(μ-NHiPr)] of hypho-type structure. 相似文献
The substitution reactions of H2GeLiF (G) with SiH3X (X = F, Cl, Br) were investigated using calculations performed at the QCISD/6-311++G (d, p)//B3LYP/6-311+G (d, p) level of theory. The results led to the following conclusions. (i) The substitutions are nucleophilic reactions. There are two substitution paths, I and II, which both lead to the germane H2GeFSiH3. The enantiomers of this germane are obtained via these two paths if an H in SiH3X is replaced with a different group or atom. (ii) Both substitution pathways show the same order of barrier heights (SiH3F > SiH3Cl > SiH3Br). The difference between the bond energies of Li–X and Si–X may explain the precedence among the substitution reactions of G with SiH3X. Path I has a lower activation barrier than path II, indicating that path I is more favorable. (iii) Comparison between the relevant insertion and substitution reactions shows that substitutions are more favorable and that the substitution product H2GeFSiH3 predominates over the insertion product. (iv) The substitution reactions of H2GeLiF with SiH3X are exothermic. 相似文献
Quantum chemical calculations were performed for LiNH2–HMgX (X?=?H, F, Cl, Br, CH3, OH, and NH2) complexes to propose a new interaction mechanism between them. This theoretical survey showed that the complexes are stabilized through the combinative interaction of magnesium and lithium bonds. The binding energies are in the range of 63.2–66.5 kcal mol?1, i.e., much larger than that of the lithium bond. Upon complexation, both Mg–H and Li–N bonds are lengthened. Substituents increase Mg-H bond elongation and at the same time decrease Li-N bond elongation. These cyclic complexes were characterized with the presence of a ring critical point and natural population analysis charges.
Figure
A new interaction mechanism has been suggested for the LiNH2-HMgH complex. It was found that the combinative interaction of magnesium and lithium bonds is responsible for the stability of the complex. The effect of subsitutents on its stability has also been investigated 相似文献
A series of compounds [(COD)(Me2Im)RhX] (Me2Im=1,3-dimethylimidazolin-2-ylidine, X=Cl, Br, I, N3, NCO, SCN, SeCN) have been prepared and examined using X-ray diffraction and NMR spectroscopy. The synthesis and structure of [(COD)(Me2Bm)RhCl] (Me2Bm=1,3-dimethylbenzimidazolin-2-ylidine) are also reported. 相似文献
Addition compounds of Hg(CF3)2 with [Ph4P]X and [Ph4As]X in the 1:1 ratio for X = Cl, Br, I as well as in the 1:2 ratio for X = SCN, were isolated from aquaeous solution and identified by elemental analysis and infrared spectroscopy. Molar conductance of the thiocyanate compounds in nitrobenzene solution points to its complex-salt nature defined as [Ph4P]2[Hg(CF3)2(SCN)2] and [Ph4As]2[Hg(CF3)2-(SCN)2], but not for the halide compounds. However, in the monoclinic crystals of the chloride ccompound, as shown by X-ray diffractometry, pairs of [Hg(CF3)2 molecules are bridged over by two chlorides in a centro-symmetrical dimer with the CHgC bond angle of 160.5(8)° and the Hg…Cl bond length of 2.823(3) and 2.837(4) Å. The structure was refined to the R factor of 0.053. When X = CN no addition compounds were obtained, the reaction products were HCF3 and the complex salts [Ph4P]2- [Hg(CN)]4 and [Ph4As]2[Hg(CN)]4, not described so far. 相似文献
Reactions of lithium halide (LiX, X = F, Cl, Br and I) and methyl halide (CH3X, X = F, Cl, Br and I) have been investigated at the B3LYP/6-31G(d) level of theory using the microhydration model. Beginning
with hydrated lithium ion, four or two water molecules have been conveniently introduced to these aqueous-phase halogen-exchange
SN2 reactions. These water molecules coordinated with the center metal lithium ion, and also interacted with entering and leaving
halogen anion via hydrogen bond in complexes and transition state, which to some extent compensated hydration of halogen anion. At 298 K the
reaction profiles all involve central barriers ΔEcent which are found to decrease in the order F > Cl > Br > I. The same trend is also found for the overall barriers (ΔEovr) of the title reaction. In the SN2 reaction of sodium iodide and methyl iodide, the activation energy agrees well with the aqueous conductometric investigation. 相似文献