Halogen Bonding or Hydrogen Bonding between 2,2,6,6-Tetramethyl- piperidine-noxyl Radical and Trihalomethanes CHX3 （X=CI, Br, I）

The halogen and hydrogen bonding complexes and trihalomethanes （CHX3, X=C1, Br, I） are between 2,2,6,6-tetramethylpiperidine-noxyl simulated by computational quantum chem- istry. The molecular electrostatic potentials, geometrical parameters and interaction energy of halogen and hydrogen bonding complexes combined with natural bond orbital analysis are obtained. The results indicate that both halogen and hydrogen bonding interactions obey the order CI〈Br〈I, and hydrogen bonding is stronger than the corresponding halogen bond- ing. So, hydrogen bonding complexes should be dominant in trihalomethanes. However, it is possible that halogen bonding complex is competitive, even preponderant, in triiodomethane due to the similar interaction energy. This work might provide useful information on specific solvent effects as well as for understanding the mechanism of nitroxide radicals as a bioprobe to interact with the halogenated compounds in biological and biochemical fields.

Molecular Dynamics Simulation Study of CIF in Water： Halogen Bonding Interaction in Liquid

Does the halogen bonding interaction co-exist in liquid when it competes with the hydrogen bonding interaction？ The classical molecular dynamics simulations for the solvation properties of CLF molecule in water are performed with the Lennard-Jones plus Coulomb electrostatic potential parameters that are optimized with ab initio interaction energy calculations for the pre-reactive H2O-CLF complex. We find that the halogen bonding interactions occur between O and CL atoms and have the comparable strength and population with respect to the hydrogen bonding interactions of C1...H.

E2/S_(N)2 Selectivity Driven by Reaction Dynamics. Insight into Halogen Bonding

Ubiquitous competition of stereospecific E2 elimination versus SN2 substitution is of central importance in chemical synthesis.Herein,we uncover how the nature of the leaving group affects the intrinsic competing dynamics that remains largely unknown as opposed to its role in reactivity.Results are presented for a prototype case of fluoride anion reacting with ethyl chloride,compared to reacting with ethyl iodide.Chemical dynamics simulations reproduce scattering signatures observed in experiments and reveal that the direct stripping/rebound mechanisms characterize the E2/S_(N)2 reactions,in line with their dynamic fingerprints identified.Quite similar structures and energetics are found for the Cl^(−)and I^(−)leaving halides,whereas the competing dynamics show markedly distinct features.A halogen-bonding attraction is found to be crucial that modifies the interaction potential in the entrance channel and essentially tunes the underlying atomistic behaviors causing a mechanistic shift.This work highlights the dynamical effects induced by a leaving group on the proceedings of baseinduced elimination and nucleophilic substitution,providing a unique insight into the reaction selectivity for complex chemical networks and environments.

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.

AIM and ELF Analyses of Halogen Bonding in NCS ： BrCl Complexes

The nature of halogen bonding in five complexes formed between the thiocyanate （NCS） radical and a BrC1 molecule was analyzed by quantum theory of atoms in molecules （QTAIM） and electron-localization function （ELF） in this paper. The calculated results show that the geometry of the halogen atom bonded at the N-atom is stable than those bonded at S- or C-atom. The molecular electrostatic potentials determine the geometries and stabilities of the complexes. The valence basin of the S- or N-atom in the electron-donating NCS radical is compressed and its population decreases during the process of formation of the halogen-bonded complexes.

CO_2 capture through halogen bonding: A theoretical perspective

Halogen bonding interactions between several halogenated ion pairs and CO2 molecules have been investigated by means of density functional theory calculations. To account for the influence of solvent environment, the implicit polarized continuum model was also employed. The bromide and iodide cations of ionic liquids (ILs) under study can interact with CO2 molecules via X O interactions, which become much stronger in strength than those in the complexes of iodo-perfluorobenzenes, very effective halogen bond donors, with CO2 molecules. Such interactions, albeit somewhat weaker in strength, are also observed between halogenated ion pairs and CO2 molecules. Thus, the solubility of CO2 may be improved when using halogenated ILs, as a result of the formation of X O halogen bonds. Under solvent effects, the strength of the interactions tends to be weakened to some degree, with a concomitant elongation of intermolecular distances. The results presented here would be very useful in the design and synthesis of novel and potent ILs for CO2 physical absorption.

Co-existing Intermolecular Halogen Bonding and Hydrogen Bonding in the Compound Trans-5,10-bis(1-bromodifluoro- acetyl-1-ethoxycarbonyl-methylidene)thianthrene

Trans-5,10-bis(1-bromodifluoroacetyl-1-ethoxycarbonyl-methylidene)thianthrene (1b) was prepared from the reaction of BrCF2COC(N2)CO2Et with thianthrene. X-ray single crystal diffraction analysis showed that the inter-molecular halogen bonding and hydrogen bonding coexisted in this compound. The bromine atom acted as an elec-tron acceptor in the halogen bond and an electron donor in the hydrogen bond. It is the first example that the bro-mine atom acted as such a dual role in the hydrogen and halogen bond.

The role of halogen bonding in improving OFET performance of a naphthalenediimide derivative

Controlling microstructure and thin film morphology of organic semiconductors by supramolecular arrangement is critical to improving their device performance. To realize well-controlling supramolecular assembly, a core-expanded naphthalene diimides derivative （1） was designed and synthesized as an n-type organic semiconductor and also as a halogen bonding （XB） donor that could form complementary XBs with 2,2-dipyridine or 2,2-bipyrimidine acceptor. The XB interactions in the solid state of 1/2,2- dipyridine and 1/2,2-bipyrimidine were confirmed by a series of characterization methods, such as thermal gravimetric analysis （TGA）, X-ray photoelectron spectroscopy （XPS）, nuclear magnetic resonance （NMR） involving 13F NMR and solid-state 13C NMR. Organic field-effect transistors （OFETs） based on XB complexes 1/2,2-dipyridine or 1/2,2-bipyrimidine showed better device performance than that of devices based on pure 1, with the average electron mobility increased more than doubled （from 0.027cm2V-1 s-1 to 0.070cm2V-1 s-1）.

Inverse Halogen Bonds Interactions Involving Br Atom in the Electronic Deficiency Systems of CH3＋… Br-Y （Y--H, CCH, CN, NC）

Inverse halogen bonds interactions involving Br in the electronic deficiency systems of CH3＋...Br-Y （Y=H, CCH, CN, NC） have been investigated by B3LYP/6- 311＋＋G（d, p） and MP2/6-311＋＋G（d, p） methods. The calculated interaction energies with basis set super-position error correction of the four IXBs complexes are 218.87, 219.48, 159.18, and 143.05kJ/mol （MP2/6-311＋＋G（d, p））, respectively. The relative stabilities of the four complexes increased in the order： CH3＋ … BrCN〈CH3＋…- BrNC〈CH3＋… BrH≈CH3＋ …BrCCH. Natural bond orbital theory analysis and the chemical shifts calculation of the related atoms revealed that the charges flow from Br-Y to CH3e. Here, the Br of Br-Y acts as both a halogen bond donor and an electron donor. Therefore, compared with conventional halogen bonds, the IXBs complexes formed between Br-Y and CH3＋. Atoms-in-molecules theory has been used to investigate the topological properties of the critical points of the four IXBs structures which have more covalent content.

Triangular Halogen Bond and Hydrogen Bond Supramolecular Complex Consisting of Carbon Tetrabromide, Halide, and Solvent Molecule： A Theoretical and Spectroscopic Study

The theoretical calculation and spectroscopic experiments indicate a kind of triangular three bonding supramolecular complexes CBr4…X^-…-H-C, which consist of carbon tetrabromide, halide, and protic solvent molecule （referring to dichloromethane, chloroform and acetonitrile）, can be formed in solution. The strength of halogen and hydrogen bonds in the triangular complexes using halide as common acceptor obeys the order of iodide〉bromide〉chloride. The halogen and hydrogen bonds work weak-cooperatively. Charge transfer bands of halogen bonding complexes between CBra and halide are observed in UV-Vis absorption spectroscopy in three solvents, and then the stoichiometry of 1：1, formation constants K and molar extinction coefficients ε of the halogen bonding complexes are obtained by Benesi-Hildebrand method. The K and ε show a dependence on the solvent dielectric constant and, on the whole, obey an order of iodide〉bromide〉chloride in the same solvents. Furthermore, the C-H vibrational frequencies of solvent molecules vary obviously with the addition of halide, which indicates the C-H…X- interaction. The experimental data indicate that the halogen bond and hydrogen bond coexist by sharing a common halide acceptor as predicted by calculation.

Ab Initio Calculations on Halogen Bond Between N—Br and Electron-donating Groups

Ab initio calculations of complexes formed between N-bromosuccinimide and a series of electron-donating groups were performed at the level of MP2/Lanl2DZ^＊ to gain a deeper insight into the nature of the N--Br halogen bonding. For the small complexes, H3 C--Br… NH3 and H2 N--Br…NH3 , the primary calculation has demonstrated that the N--Br in H2 N--Br… NH3 can form a much stronger halogen-bonding complex than the C--Br. A comparison of neutral hydrogen bond complex series reveals that the electron-donating capacities of the atoms decrease in the order, N 〉 O 〉 S; 0 （ sp^3 ） 〉 0 （ sp^2 ）, which is adequate for the C--Br halogen bonding. Interaction energies, in conjunction with the geometrical parameters show that the affinitive capacity of trihalide anions X^-3 with N-bromosuccinimide are markedly lower than that of the corresponding X^- with N-bromosuccinimide, even lower than those of neutral molecules with N-bromosueeinimide. AIM analyses further eorffirmed the above results.

Theoretical Study of the Iodine-catalyzed Nucleophilic Addition by Halogen Bond

The iodine-catalyzed nucleophilic addition of pyrrole to acetone has been studied by density functional theory at the level of Lanl2DZ＊. It has been shown that the first iodine molecule appears to have a remarkable catalytic effect on this reaction by halogen bond between carbonyl oxygen and iodine molecule, but the second one does not improve the reaction largely. In general, the nucleophilic addition at the C（2） site of pyrrole is more favorable than that at the C（3） site; however, this trend is not prominent or even changed in acetronitrile solvent for the indole system, which is consistent with the experimental result by Bandgar.

Investigation of Intermolecular C-H···Halogen Hydrogen Bonded Supramolecular Assemblies in Three Copper(Ⅰ) Complexes Formed by 3,3'-Dimethoxy-6,6'-dimethyl-2,2'-bipyridine Ligand

Three new crystalline compounds 1-3 were successfully obtained by the reactions of 3,3＇-dimethoxy-6,6＇-dimethyl-2,2＇-bipyridine ligand（dmbp） with the corresponding Cu（Ⅰ） salts.Crystal data for 1：orthorhombic Pbca,a = 18.5858（12）,b = 8.1821（5）,c = 20.6066（13） ,V = 3133.7（3） 3,Z = 8,Dc = 1.843 g/cm3,F（000） = 1696,μ = 3.366 mm-1,the final R = 0.0223 and wR = 0.0542.Crystal data for 2：Orthorhombic Pbca,a = 18.7883（16）,b = 8.3249（7）,c = 19.0294（17） ,V = 2976.4（4） 3,Z = 8,Dc = 1.731 g/cm3,F（000） = 1552,μ = 4.154 mm-1,the final R = 0.0279 and wR = 0.0680.Crystal data for 3：monoclinic P21/c,a = 13.812（10）,b = 9.910（7）,c = 23.444（17） ,β = 104.3350（10）°,V = 3090（4） 3,Z = 4,Dc = 1.476 g/cm3,F（000） = 1408,μ = 1.588 mm-1,the final R = 0.0479 and wR = 0.1081.The results of X-ray crystallographic analysis revealed that C14H16ICuN2O2（1） and C14H16BrCuN2O2（2） are isostructural compounds with the dimers connected by C-H···halogen hydrogen bonds to generate a three-dimensional（3D） supramolecular network in 1 and a two-dimensional（2D） sheet structure in 2,respectively,while the mononuclear complex C28H32Cl2Cu2N4O4（3） is ionic.In 3,the [Cu（dmbp）2]＋ cations and [ClCuCl]-anions are connected by C-H···Cl hydrogen bonds to form a one-dimensional（1D） chain along the a axis.Therefore,in the three complexes,the C-H···halogen hydrogen bonds dominate their crystal structures.Additionally,The UV luminescent properties of complexes 1-3 were investigated.

Investigation of the Substituent Effects on π-Type Pnicogen Bond Interaction

Intermolecular interactions between PH2Cl and Ar–R（R = H,OH,NH2,CH3,Br,Cl,F,CN,NO2） were calculated by using MP2/aug-cc-p VDZ quantum chemical method.It has been shown from our calculations that the aromatic rings with electron-withdrawing groups represent much weaker binding affinities than those with electron-donating groups.The charge-transfer interaction between PH2Cl and Ar–R plays an important role in the formation of pnicogen bond complexes,as revealed by NBO analysis.Nevertheless,AIM analysis shows that the nature of the interactions between PH2Cl and Ar–R is electrostatic,and the interaction energies of the complexes are correlated positively with the electron densities in the bond critical points（BCPs）.RDG/ELF graphical analyses were performed to visualize the positions and strengths of the pnicogen bonding,as well as the spatial change of the electron localization upon the formation of complexes.The π-type halogen bond was also calculated,and it has been revealed that the π-type pnicogen bond systems are more stable than the halogen bond ones.

Theoretical Studies on the Iodine-catalyzed Nucleophilic Addition of Acetone with Five-membered Heterocycles

The iodine-catalyzed nucleophilic addition reactions of pyrrole, furan, or thiophene with acetone were studied in gas and solvent by the density functional theory at the level of Lanl2DZ^＊. It was seen that the halogen bond between iodine and carbonyl oxygen appeared to have an important catalytic effect on such reactions, and the first iodine molecule maximally diminished the barrier height by 41 kJ/mol, while the second iodine molecule could not improve such reactions largely. It was concluded that the C2-addition was generally more favorable than the C3-addition for the three heterocycles; however, iodine considerably more effectively catalyzed the C3-addition than the C2-addition for pyrrole. It was also revealed by PCM calculation that the iodine-catalyzed nucleophilic additions occurred more easily in solvent than in gas, which explained the experiment performed by Bandgar et al..

Electrophilic Halogen Reagents-mediated Halogenation: Synthesis of Halogenated Dihydro-1,3-oxazine Derivatives

Halogenation of N-cinnamylbenzamides and N-[(2H-chromen-3-yl)methyl]benzamides using electrophilic halogen source was reported.Various halogenated dihydro-1,3-oxazine derivatives(45 examples)were synthesized in high to excellent yields(up to 98%yields),as well as halogenated dihydrochromeno-1,3-oxazine derivatives(56 examples,up to 96%yields).The properties of mild conditions,metal-free and high efficiency of the reaction made it a promising strategy in future applications for the construction of carbon-halogen(fluorine,F;chlorine,Cl;bromine,Br;iodine,I)bond and 1,3-oxazine derivatives.

Chiral supramolecular 2D halogen-bonded organic frameworks constructed by post-synthetic modified cross-linking strategy

The development of preparation methods for XOFs,as a new class of organic frameworks,plays a crucial role in shaping their structures,functions,and potential applications.In this study,we presented the construction of chiral supramolecular 2D halogen-bonded organic frameworks(XOFs)through a post-synthetic modification strategy.A linear halogen-bonded organic polymer(XOP),XOP-DPBA,decorated with aldehyde groups,was initially prepared to validate the feasibility of post-synthetic modification for XOF construction and functionalization.XOP-DPBA exhibited excellent reactivity with amines,forming imine bonds.By utilizing this reactivity,a series of cross-linked 2D XOFs were efficiently prepared through post-synthetic modified cross-linking reactions.Furthermore,we successfully introduced chiralα/β-cyclodextrins(α/β-CD)into the XOF skeletons via host-guest interactions,resulting in the fabrication of chiral supramolecular 2D XOFs.These chiral XOFs displayed the induced circular dichroism(ICD)signals and assembled them into helical fibers.The post-synthetic modification strategy demonstrated its versatility and simplicity for the construction and functionalization of XOFs.

Achieving tunable long persistent luminescence in metal organic halides based on pyridine solvent

The research of long persistent luminescence(LPL)materials has yield brilliant results in many fields.However,the efforts are still needed for the regulation of the LPL performance.In this work,a series of LPL metal organic halides with rich halogen-bond interactions,Py-CdX_(2)(X=Cl,Br,I)were synthesized through self-assembly by Cd X_(2)and pyridine solvent.The steady-state emission redshifted and phosphorescence lifetime declined as the halogen atoms are aggravated.Three halides exhibit adjustable emission from blue to green and multiple phosphorescence from green to yellow at room temperature by changing the excitation wavelengths.Surprisingly,Py-CdX_(2)can emit the visible color-tunable LPL from green to yellow after removing different excitation sources at ambient conditions.Combing the results of theoretical calculation and experimental analysis,it is found that heavy atom effect and the rich intermolecular halogen bond help realize LPL and multiple triplet states originated from the pyridine ring and the halogens.

Halogen-bonded Cocrystal Based on Tetrathiafulvalene Derivatives

In this paper, two cocrystals 1 and 2 with the same chemical composition [L1.L2 ](L1 = bis(4’-pyridyl)-TTF, L2 = 4,4’-diiodophenyl) were synthesized by slow diffusion with different solvent systems. Cocrystals 1 and 2 were characterized by single-crystal X-ray and the purity of these two cocrystals was confirmed by PXRD data. The photocurrent responses of these two cocrystals were also tested. Only cocrystal 1 could generate photocurrent signal when exposed to light. From the crystal structure analysis, the possible reason may come from the different biphenyl conformations in L2.

Halogen Bond Catalysis on Carbonyl-Olefin Ring-Closing Metathesis Reaction:Comparison with Lewis Acid Catalysis

The carbonyl-olefin ring-closing metathesis reactions have become a powerful tool for carbon-carbon bond formation.In this work,the halogen bond catalysis and classical Lewis acid catalysis on the carbonyl-olefin ring-closing metathesis reaction were investigated by density function theory.For both the halogen bond catalysis and classical Lewis acid catalysis,the carbonyl-olefin ring-closing me-tathesis reaction occurs by[2+2]-cycloaddition process and[2+2]-cycloreversion process,the reaction energy barriers are low,there-fore,it can be performed easily at room temperature.The essential difference of the two kinds of catalysts is that the catalytic mecha-nism of halogen bond catalysis is mainly contribution of electrostatic interaction,while that of classical Lewis acid catalysis is mainly catalyzed by orbital interaction.The halogen bond donor catalysts(ICI_(3),IF_(3))are expected to be efficient catalysts for the reaction and further promote the chemical synthesis of carbonyl-olefin ring-closing metathesis reaction.