Halogen Bonds of Halotetrafluoropyridines in Crystals and Co-crystals with Benzene and Pyridine

The structures of the three para-substituted halotetrafluoropyridines with chlorine, bromine, and iodine have been determined in the solid state (X-ray diffraction). The structures of these compounds and that of pentafluoropyridine were also determined in the gas phase (electron diffraction). Structures in the solid state of the bromine and iodine derivatives exhibit halogen bonding as a structure-determining motif. On the way to an investigation of halogen bond formation of halotetrafluoropyridines in the solid state with the stronger Lewis base pyridine, co-crystals of benzene adducts were investigated to gain an understanding of the influence of aryl–aryl interactions. These co-crystals showed halogen bonding only for the two heavier halotetrafluoropyridines. In the pyridine co-crystals halogen bonding was observed for all three para-halotetrafluoropyridines. The formation of homodimers and heterodimers with pyridine is also supported by quantum-chemical calculations of electron density topologies and natural bond orbitals.     

Comparison of non-covalent interactions and spectral properties in 1-methyl-3-methylthio-5-phenyl-1,2,4-triazinium mono- and tetraiodide crystals

The reaction of 1-methyl-3-methylthio-5-phenyl-1,2,4-triazinium (MTPT) iodide with diiodine in a solution leads to monoiodide crystal structure that in excess of iodine gives the unusual tetraiodide anion with two central iodine atoms in disorder. The bonding within the anion has been characterized as I^–…I₂…I^–; the existence of the bound iodine molecule inside has been proven by the characteristic band in experimental and calculated Raman spectra. Non-covalent interactions of MTPT in considered crystal structures are different. Monoiodide anion as a strong electron donor allows the formation of the S…I chalcogen bonds that are absent in tetraiodide structure. The features of halogen bonds within the I₄^2– anion are also performed.

     

Secondary Bonding,C═H…O Hydrogen Bonding Assisted Supramolecular Associations and Charge Transfer (CT) Complexes of Organotelluriums and their Nonlinear Optical Properties

Abstract

A library of supramolecular assemblies of acyclic- and cyclic organotelluriums assisted by intermolecular Te… X (X = Cl, Br, I, O, S) secondary bonds has been synthesized and X-ray characterized. In each case the immediate coordination geometry around the central Te atom is pseudotrigonal bipyramidal in which two methylene carbon atoms (attached to Te) in cyclic organotelluriums and methyl carbon atoms in acyclic organotelluriums and the stereochemically active electron lone pair occupy equatorial positions whereas the axial positions are occupied by halogen, oxygen or sulphur. They exists either as (a) ordered oligomers (trimeric, tetrameric, octameric aggregates) (b) cross linked chains, (c) zig-zag ?2 dimensional ribbons and stairs, and (d) 3-dimensional supramolecular networks. It is observed that the supramolecular associations assisted by Te…O and Te…S secondary bonds are modified whereas those assisted by Te…halogen remain more or less the same vis-à-vis the supramolecular associations present in their precursors in the solid state. The first detection of C─H…O hydrogen bonds in organotellurium compounds has been done and their use in the synthesis of tellurium essential and ligand essential supramolecular assemblies is demonstrated. Tetraorganotelluroxanes obtained by easy and efficient routes represent the examples of cooperative participation of intermolecular and intramolecular Te…O secondary bonds and C─H…O hydrogen bonds. Hypervalent Te─I (formed through n → σ* orbital interactions) bonds in cyclic telluranes act as potential synthons for the formation of CT complexes possessing unusual structures. The utility of organotelluriums in the serendipitous synthesis of the first triphenyl methyl phosphonium salts of [C₄H₈TeI₄]^2? and [TeI₆]^2? anions is shown. The second harmonic generation (SHG) efficiency of some of these new supramolecular assemblies of organotelluriums indicates that the presence of C─H…O hydrogen bonds enhances their non linear optical (NLO) properties.     

Single‐electron halogen bond: Ab initio study

Ab initio calculations have been performed on single‐electron halogen bonds between methyl radical and bromine‐containing molecules to gain a deeper insight into the nature of such noncovalent interactions. Bader's atoms in molecules (AIM) theory have also been applied to the analysis of the linking of the single‐electron halogen bond. Various characteristics of the R? Br…CH₃ interaction, i.e., binding energies, geometrical parameters and topological properties of the electron density have been determined. The presence of the bond critical points (BCPs) between the bromine atom and methyl radical and the values of electron density and Laplacian of electron density at these BCPs indicate the closed‐shell interactions in the complexes. The single‐electron halogen bonds, which are significantly weaker than the normal halogen bonds, exhibit equally bond strength as compared to the single‐electron hydrogen bond. It has been also found that plotting of the binding energies versus topological properties of the electron density at the BCPs gives two straight lines. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Triangular halogen trimers. A DFT study of the structure, cooperativity, and vibrational properties

Triangular halogen trimers (RX)3, where X = Br, I and R represents H, H3C, H2FC, HF2C, F3C, CH2=CH, CH[triple bond]C, and Ph, have been investigated using the density functional theory in the Perdew, Burke, and Ernzerhof method. We report herein the optimized geometries of the stable structures, their vibrational frequencies, and binding energies with the two- and three-body terms. All trimer structures possess a cyclic array of halogen atoms in the type II approach by virtue of the nonspherical atomic charge distribution around the halogens. The Br...Br interactions in trimers are very weak, whereas the I...I interactions in trimers are relatively stronger. While all bromine trimers and most of iodine trimers are predicted to be noncooperative, three of iodine trimers show weak cooperativity. The analysis of vibration modes reveals that all halogen trimers exhibit no especially remarkable frequency shifts. It is also shown that the electrostatic contribution plays a major role in the halogen...halogen interactions in halogen trimers. In contrast to bromine trimers, the relative contribution of charge-transfer component to the halogen...halogen interactions becomes more important for iodine trimers.     

The many flavours of halogen bonds – message from experimental electron density and Raman spectroscopy

Experimental electron‐density studies based on high‐resolution diffraction experiments allow halogen bonds between heavy halogens to be classified. The topological properties of the electron density in Cl…Cl contacts vary smoothly as a function of the interaction distance. The situation is less straightforward for halogen bonds between iodine and small electronegative nucleophiles, such as nitrogen or oxygen, where the electron density in the bond critical point does not simply increase for shorter distances. The number of successful charge–density studies involving iodine is small, but at least individual examples for three cases have been observed. (a) Very short halogen bonds between electron‐rich nucleophiles and heavy halogen atoms resemble three‐centre–four‐electron bonds, with a rather symmetric heavy halogen and without an appreciable σ hole. (b) For a narrow intermediate range of halogen bonds, the asymmetric electronic situation for the heavy halogen with a pronounced σ hole leads to rather low electron density in the (3,?1) critical point of the halogen bond; the properties of this bond critical point cannot fully describe the nature of the associated interaction. (c) For longer and presumably weaker contacts, the electron density in the halogen bond critical point is only to a minor extent reduced by the presence of the σ hole and hence may be higher than in the aforementioned case. In addition to the electron density and its derived properties, the halogen–carbon bond distance opposite to the σ hole and the Raman frequency for the associated vibration emerge as alternative criteria to gauge the halogen‐bond strength. We find exceptionally long C—I distances for tetrafluorodiiodobenzene molecules in cocrystals with short halogen bonds and a significant red shift for their Raman vibrations.     

Supramolecule-regulated photophysics of oligo(p-phenyleneethynylene)-based rod-coil block copolymers: effect of molecular architecture

Three new topology-varied rod-coil block copolymers, comprising the same oligo(p-phenyleneethynylene) (OPE) rod components and the same coil components, were synthesized by atom-transfer radical polymerization. Their photophysical properties were systematically studied and compared in consideration of their solid-state structures and self-assembly abilities. These copolymers have similar intrinsic photophysical properties to the OPE rods, as reflected in dilute solution. However, their photophysical properties in the solid state are manipulated to be dissimilar by supramolecular organization. Wide-angle X-ray diffraction (WAXD) and atomic force microscopy (AFM) data demonstrate that these copolymers possess different self-assembly abilities due to the molecular-architecture-dependent pi-pi interactions of the rods. Hence, the aggregates in the solid state are formed with a different mechanism for these copolymers, bringing about the discrepancy in the solid-state luminescent properties.     

Stereochemical features of bromine- and iodine-containing compounds of lanthanides

The Voronoi-Dirichlet (VD) polyhedra and the intersecting spheres method have been used to analyze the features of the environment of lanthanide (Ln) atoms consisting of bromine and iodine atoms in the structures of 94 compounds containing 96 LnBr _n complexes and 41 LnI _n complexes. The lanthanum CN with respect to halogen atoms varies from 6 to 9. The volume of the VD polyhedra of Ln atoms depends only on the oxidation state of the metal atom and the nature of the surrounding atoms.     

Spectrophotometric study of the reaction of iodine and bromine with two new macrocycle diamides and di-ortho methoxybenzoyl thiourea in chloroform solution

The complex formation reactions of iodine and bromine with two new macrocycle diamides (1 and 2) and di-ortho methoxybenzoyl thiourea (DOMBT) (3) have been studied spectrophotometrically at various temperatures in chloroform solution. In all cases the resulting 1:2 (macrocycle to halogen) or (DOMBT to halogen) molecular complexes were formulated as (macrocycle...X(+))X(3)(-) or (DOMBT.... X(+))X(3)(-). The formation constants of the resulting molecular complexes were evaluated from computer fitting of the absorbance-mole ratio data. For iodine complexes we found that the values of K(f) vary in the order of 1 approximately 2>3. In the case of bromine complexes the values of K(f) are larger (>10(8)) and vary in the order of 1>2>3. The enthalpy and entropy of complexation reactions of iodine with 1, 2 and 3 were determined from the temperature dependence of the formation constants. In all cases it was found that the complexation reactions are enthalpy stabilized, but entropy destabilized.     

Comparative Study of Halogen‐ and Hydrogen‐Bond Interactions between Benzene Derivatives and Dimethyl Sulfoxide

The halogen bond, similar to the hydrogen bond, is an important noncovalent interaction and plays important roles in diverse chemistry‐related fields. Herein, bromine‐ and iodine‐based halogen‐bonding interactions between two benzene derivatives (C₆F₅Br and C₆F₅I) and dimethyl sulfoxide (DMSO) are investigated by using IR and NMR spectroscopy and ab initio calculations. The results are compared with those of interactions between C₆F₅Cl/C₆F₅H and DMSO. First, the interaction energy of the hydrogen bond is stronger than those of bromine‐ and chlorine‐based halogen bonds, but weaker than iodine‐based halogen bond. Second, attractive energies depend on 1/rⁿ, in which n is between three and four for both hydrogen and halogen bonds, whereas all repulsive energies are found to depend on 1/r^8.5. Third, the directionality of halogen bonds is greater than that of the hydrogen bond. The bromine‐ and iodine‐based halogen bonds are strict in this regard and the chlorine‐based halogen bond only slightly deviates from 180°. The directional order is iodine‐based halogen bond>bromine‐based halogen bond>chlorine‐based halogen bond>hydrogen bond. Fourth, upon the formation of hydrogen and halogen bonds, charge transfers from DMSO to the hydrogen‐ and halogen‐bond donors. The CH₃ group contributes positively to stabilization of the complexes.     

Nontypical iodine–halogen bonds in the crystal structure of (3E)‐8‐chloro‐3‐iodomethylidene‐2,3‐dihydro‐1,4‐oxazino[2,3,4‐ij]quinolin‐4‐ium triiodide

Two kinds of iodine–iodine halogen bonds are the focus of our attention in the crystal structure of the title salt, C₁₂H₈ClINO⁺·I₃⁻, described by X‐ray diffraction. The first kind is a halogen bond, reinforced by charges, between the I atom of the heterocyclic cation and the triiodide anion. The second kind is the rare case of a halogen bond between the terminal atoms of neighbouring triiodide anions. The influence of relatively weakly bound iodine inside an asymmetric triiodide anion on the thermal and Raman spectroscopic properties has been demonstrated.     

Symmetric halogen bonding is preferred in solution

Halogen bonding is a recently rediscovered secondary interaction that shows potential to become a complementary molecular tool to hydrogen bonding in rational drug design and in material sciences. Whereas hydrogen bond symmetry has been the subject of systematic studies for decades, the understanding of the analogous three-center halogen bonds is yet in its infancy. The isotopic perturbation of equilibrium (IPE) technique with (13)C NMR detection was applied to regioselectively deuterated pyridine complexes to investigate the symmetry of [N-I-N](+) and [N-Br-N](+) halogen bonding in solution. Preference for a symmetric arrangement was observed for both a freely adjustable and for a conformationally restricted [N-X-N](+) model system, as also confirmed by computation on the DFT level. A closely attached counterion is shown to be compatible with the preferred symmetric arrangement. The experimental observations and computational predictions reveal a high energetic gain upon formation of symmetric, three-center four-electron halogen bonding. Whereas hydrogen bonds are generally asymmetric in solution and symmetric in the crystalline state, the analogous bromine and iodine centered halogen bonds prefer symmetric arrangement in solution.     

过渡金属M (M=Cu,Ag, Au)对X…Cl (X = F,Cl, Br)卤键相互作用强度的影响

采用量子化学方法,通过MCH2X…ClF(M=Cu,Ag,Au;X=F,Cl,Br)和CH3X…ClF两类复合物的对比,探讨了过渡金属对卤键相互作用强度的影响.CH3X…ClF复合物只有卤键相互作用,而优化MCH2X…ClF复合物除了得到一种只含有卤键相互作用的构型外,还得到一种含有过渡金属和Cl原子相互作用的稳定构型.含有过渡金属的复合物稳定性明显增加,Ag取代的复合物稳定性增加最为明显,Cu次之,Au最不明显.X原子最负分子表面静电势(MEP)减小是复合物稳定性增加的根本原因.利用自然键轨道(NBO)及分子中原子(AIM)分析进一步对体系的分子间相互作用进行了探讨.二阶稳定化能与键鞍点处拓扑性质的计算结果与相互作用能符合得很好.     

Molecular Packing and Solid-State Photophysical Properties of 1,3,6,8-Tetraalkylpyrenes

The relationship between the photophysical properties and molecular orientation of 1,3,6,8-tetraalkylpyrenes in the solid state is described herein. The introduction of alkyl groups with different chain structures (in terms of length and branching) did not affect the photophysical properties in solution, but significantly shifted the emission wavelengths and fluorescence quantum yields in the solid state for some samples. Pyrenes bearing ethyl, isobutyl, or neopentyl groups at the 1-, 3-, 6-, and 8-positions showed similar emission profiles in both the solution and solid states. In contrast, pyrenes bearing other alkyl groups exhibited an excimer emission in the solid state, similar to that of the parent pyrene. On studying the photophysical properties in the solid state with respect to the obtained crystal structures, the observed solid-state photophysical properties were found to depend on the relative position of the pyrene chromophores. The solid-state photophysical properties can be controlled by the alkyl groups, which provide changing crystal packing. Among the pyrenes tested, 1,3,6,8-tetraethylpyrene showed the highest fluorescence quantum yield of 0.88 in the solid state.     

Halogenation of Graphene with Chlorine,Bromine, or Iodine by Exfoliation in a Halogen Atmosphere

Nanoarchitectonics on graphene implicates a specific and exact anchoring of molecules or nanoparticles onto the surface of graphene. One such example of an effective anchoring group that is highly reactive is the halogen moiety. Herein we describe a simple and scalable method for the introduction of halogen (chlorine, bromine, and iodine) moieties onto the surface of graphene by thermal exfoliation/reduction of graphite oxide in the corresponding gaseous halogen atmosphere. We characterized the halogenated graphene by using various techniques, including scanning and transmission electron microscopy, Raman spectroscopy, high‐resolution X‐ray photoelectron spectroscopy, and electrochemistry. The halogen atoms that have successfully been attached to the graphene surfaces will serve as basic building blocks for further graphene nanoarchitectonics.     

Photochemical cleavage reaction of 8-quinolinyl sulfonates that are halogenated and nitrated at the 7-position

Photochemical bond-cleavage reactions are potentially useful in chemistry, bioorganic chemistry and medicinal chemistry. We previously reported on a photochemical cleavage reaction of 8-quinolinyl sulfonate (8-QS) derivatives in aqueous solution at neutral pH, which we proposed to proceed via an excited triplet state. In this report, we report on the synthesis of some new photocleavable 8-QS derivatives, in which halogen atoms or a nitro group was introduced at the 7-position, in an attempt to improve photoreactive properties and to produce a red-shift in the irradiation wavelength. The introduction of bromine and iodine resulted in an acceleration in the photoreaction by about 1.5 times, possibly due to a heavy atom effect. It was also found that 7-nitro-8-QS absorbs at >360 nm, and, as a result, the S-O bond of this compound can be cleaved by photoirradiation with a fluorescent lamp in aqueous solution and on silicon surface.     

萘氧乙酸及咪唑构筑的锌(Ⅱ)和铜(Ⅱ)配合物的水热合成、晶体结构及荧光性质

通过水热的方法合成得到2个由萘氧乙酸及咪唑配体构筑的配合物Zn(2-naph)₂(imi)₂ (1)和2Cu(2-naph)₂(imi)₂(H₂O)·Cu(2-naph)₂(imi)₂(H₂O) (2)(2-naph=2-naphthoxyacetate,imi=imidazole),它们的结构通过X射线晶体衍射、红外光谱和元素分析得到确定。在配合物1中,锌原子与来自不同2-萘氧乙酸配体中的2个羧酸氧原子和不同的咪唑分子中的2个氮原子形成了变形的四面体的几何构型。单个分子通过N-H…O氢键连接形成了一维链,然后在C-H…π弱作用下形成了三维结构。配合物2有2个独立的铜中心,它们有几乎相同的配位环境。每个铜中心都是变形的四方锥的配位构型。来自不同的2-萘氧乙酸配体中的2个羧酸氧原子和不同的咪唑分子中的2个氮原子形成了一个相对规则的四方锥赤道平面,配位水分子位于平面上方。配合物2的分子通过N-H…O和O-H…O氢键连接形成了二维结构。2个配合物的热稳定和固体荧光性质在本文中也得到了研究和讨论。     

Self‐Assembly of Iodine in Superfluid Helium Droplets: Halogen Bonds and Nanocrystals

We present evidence of halogen bond in iodine clusters formed in superfluid helium droplets based on results from electron diffraction. Iodine crystals are known to form layered structures with intralayer halogen bonds, with interatomic distances shorter than the sum of the van der Waals radii of the two neighboring atoms. The diffraction profile of dimer dominated clusters embedded in helium droplets reveals an interatomic distance of 3.65 Å, much closer to the value of 3.5 Å in iodine crystals than to the van der Waals distance of 4.3 Å. The profile from larger iodine clusters deviates from a single layer structure; instead, a bi‐layer structure qualitatively fits the experimental data. This work highlights the possibility of small halogen bonded iodine clusters, albeit in a perhaps limited environment of superfluid helium droplets. The role of superfluid helium in guiding the trapped molecules into local potential minima awaits further investigation.     

Structures and electronic properties of Al7x0,- and Al13 X1,2,12- clusters with X=F, Cl, and Br

The structures, binding energies, and electronic properties for Al7X, Al7X-, Al13X-, Al13X2-, and Al13X12- (X = F, Cl, Br) were studied at the B3LYP/6-311+G(2d,p) level. Among the systems studied, Al7 and Al13 clusters in Al7X and Al13X- reveal alkali-like and halogen-like superatom characters, respectively. Al7 can bind with one halogen atom to form a salt-like compound as Al7+delta-X-delta. Al13- can combine with one halogen atom to form a diatomic halogen anion Al13X-. However, when adding more halogens, the superatom structure would be destroyed, resulting in low-symmetry compounds with the center Al atom moving toward the cluster surface. The structures of Al13X1,2,12- (X = F, Cl, Br) are similar to those of X = I; however, their binding energies and electron structures are much different. In addition, the analyses of the calculated NBO charges show that Cl and Br have similar properties, but much different from F, when interacting with the Al clusters. The Al-Cl and Al-Br bonds have more covalent character in Al7X and Al13X2,12-, in contrast to the corresponding Al-F bond, which has prominent ionic character.