Preparation and structure of chlorinated poly(vinyl flouride)

The low-temperature chlorination of poly(vinyl fluoride) (PVF) proceeds readily in CCl₄ suspension. The rate of chlorination is high initially, but the reaction slows down considerably when the chlorine content of the polymer reaches 40–50%. At long reaction times, polymers containing 62% chlorine (1.88 chlorine atoms per monomer unit) can be obtained. As the degree of chlorination increases, the solubility of PVF in organic solvents increases. Polymer crystallinity and polymer softening point decrease with chlorination. Polymers containing 40% chlorine appear to be completely amorphous by x-ray analysis. In this respect, PVF differs from poly(vinyl chloride) (PVC), where chlorination increases the softening point, and it resembles polyethylene where both crystallinity and softening point decrease with chlorination. ¹⁹F NMR analysis of the polymers indicates that up to a degree of chlorination of 1 chlorine atom per monomer unit, 50% of the substitution occurs on the α-carbon of the PVF molecule. This result is very different from the predominant β-chlorination of PVC reported by several workers. The chemical selectivity observed in the chlorination of PVF is in quantitative agreement with the results of free-radical chlorination of organic compounds and can be rationalized by considering the size and the electronic properties of the fluorine atom. The results of ¹H NMR analysis are also in support of a polymer structure where the chlorine atoms are distributed between α- and β-carbons. Based on a comparison of the ¹⁹F and ¹H NMR data, the average composition of chlorinated PVF at the 1 chlorine atom per monomer unit level can be represented as: C₂₀₀H₂₀₀F₁₀₀Cl₁₀₀ = (CH₂)₆₃(CHF)₅₀(CHCl)₂₄(CClF)₅₀-(CCl₂)₁₃.     

Gold(I)‐Catalyzed Haloalkynylation of Aryl Alkynes: Two Pathways,One Goal

Haloalkynylation reactions provide an efficient method for the simultaneous introduction of a halogen atom and an acetylenic unit. For the first time, we report a gold(I)‐catalyzed haloalkynylation of aryl alkynes that delivers exclusively the cis addition product. This method enables the simple synthesis of conjugated and halogenated enynes in yields of up to 90 %. Notably, quantum chemical calculations reveal an exceptional interplay between the place of the attack at the chloroacetylene: No matter which C?C bond is formed, the same enyne product is always formed. This is only possible through rearrangement of the corresponding skeleton. Hereby, one reaction pathway proceeds via a chloronium ion with a subsequent aryl shift; in the second case the corresponding vinyl cation is stabilized by a 1,3‐chlorine shift. ¹³C‐labeling experiments confirmed that the reaction proceeds through both reaction pathways.     

Influence of Backbone Chlorination on the Electronic Properties of Diketopyrrolopyrrole (DPP)‐Based Dimers

Chlorination of π‐conjugated backbones is garnering great interest because of fine‐tuning electronic properties of conjugated materials for organic devices. Herein we report a synthesis of thiophene‐based diketopyrrolopyrrole (DPP) dimers and their chlorinated counterparts by introducing a chlorine atom in the outer thiophene ring to investigate the influence of the chlorination on charge transport. The backbone chlorination lowers both the HOMO and the LUMO of the dimers and leads to a blue‐shift of maximum absorption in compared to unsubstituted counterparts. X‐ray analysis reveals that the chlorine atom prompts the outer thiophene ring out of the planarity of the backbone with a relatively large torsional angle. The chlorinated dimers exhibit slipped one‐dimensional packing decorated with multiple intermolecular interactions, because of a combination of a negative inductive effect and a positive mesomeric effect of the halogen atom, which might facilitate charge transport within the oligomeric backbones. The mobility in the single‐crystal OFET devices of the chlorinated dimers is up to 1.5 cm² V^?1 s^?1, which is two times higher than that of the non‐chlorinated DPP dimers. Our results indicate that the chlorine atom plays a key role in directing non‐covalent interactions to lock the slipped stacks, enabling electronic coupling between adjacent molecules for efficient charge transport. In addition, our results also demonstrate that these DPP dimers with straight n‐octyl chains exhibit higher mobilities than the dimers with branched 2‐ethylhexyl chains.     

Comparison of Hydrogen and Gold Bonding in [XHX]−, [XAuX]−, and Isoelectronic [NgHNg]+, [NgAuNg]+ (X=Halogen,Ng=Noble Gas)

Quantum chemical calculations at the MP2/aug‐cc‐pVTZ and CCSD(T)/aug‐cc‐pVTZ levels have been carried out for the title compounds. The electronic structures were analyzed with a variety of charge and energy partitioning methods. All molecules possess linear equilibrium structures with D_∞h symmetry. The total bond dissociation energies (BDEs) of the strongly bonded halogen anions [XHX]^? and [XAuX]^? decrease from [FHF]^? to [IHI]^? and from [FAuF]^? to [IAuI]^?. The BDEs of the noble gas compounds [NgHNg]⁺ and [NgAuNg]⁺ become larger for the heavier atoms. The central hydrogen and gold atoms carry partial positive charges in the cations and even in the anions, except for [IAuI]^?, in which case the gold atom has a small negative charge of ?0.03 e. The molecular electrostatic potentials reveal that the regions of the most positive or negative charges may not agree with the partial charges of the atoms, because the spatial distribution of the electronic charge needs to be considered. The bonding analysis with the QTAIM method suggests a significant covalent character for the hydrogen bonds to the noble gas atoms in [NgHNg]⁺ and to the halogen atoms in [XHX]^?. The covalent character of the bonding in the gold systems [NgAuNg]⁺ and [XAuX]^? is smaller than in the hydrogen compound. The energy decomposition analysis suggests that the lighter hydrogen systems possess dative bonds X^?→H⁺←X^? or Ng→H⁺←Ng while the heavier homologues exhibit electron sharing through two‐electron, three‐center bonds. Dative bonds X^?→Au⁺←X^? and Ng→Au⁺←Ng are also diagnosed for the lighter gold systems, but the heavier compounds possess electron‐shared bonds.     

Halogenation of trifluoromethoxy and bis(trifluoromethoxy)benzene

Controlled chlorination of trifluoromethoxybenzene produced the mono-, di-, tri-, and tetrachloro derivatives. Two isomers were detected at each level of substitution. Exhaustive chlorination and bromination of 1,3- and 1,4-bis(trifluoromethoxy)-benzene yielded isomeric mixtures of only the disubstituted bis(trifluoromethoxy)benzenes. No hydrolysis of the -OCF₃ group was detected in any halogenations. The configuration of all the products was determined by ¹H and ¹⁹F nmr. A through-space hydrogen-fluorine coupling of 0.7 – 1.3Hz between the -OCF₃ substituent and the ortho proton was observed in all the halogenated products. The polychlorinated derivatives all exhibited good thermal stability at 200°–250°.     

Endohedral and Exohedral Metalloborospherenes: M@B40 (M=Ca,Sr) and M&B40 (M=Be,Mg)

The recent discovery of the all‐boron fullerenes or borospherenes, D_2d B₄₀^−/0, paves the way for borospherene chemistry. Here we report a density functional theory study on the viability of metalloborospherenes: endohedral M@B₄₀ (M=Ca, Sr) and exohedral M&B₄₀ (M=Be, Mg). Extensive global structural searches indicate that Ca@B₄₀ ( 1 , C_2v, ¹A₁) and Sr@B₄₀ ( 3 , D_2d, ¹A₁) possess almost perfect endohedral borospherene structures with a metal atom at the center, while Be&B₄₀ ( 5 , C_s, ¹A′) and Mg&B₄₀ ( 7 , C_s, ¹A′) favor exohedral borospherene geometries with a η⁷‐M atom face‐capping a heptagon on the waist. Metalloborospherenes provide indirect evidence for the robustness of the borospherene structural motif. The metalloborospherenes are characterized as charge‐transfer complexes (M²⁺B₄₀²⁻), where an alkaline earth metal atom donates two electrons to the B₄₀ cage. The high stability of endohedral Ca@B₄₀ ( 1 ) and Sr@B₄₀ ( 3 ) is due to the match in size between the host cage and the dopant. Bonding analyses indicate that all 122 valence electrons in the systems are delocalized as σ or π bonds, being distributed evenly on the cage surface, akin to the D_2d B₄₀ borospherene.     

Endohedral and Exohedral Metalloborospherenes: M@B40 (M=Ca,Sr) and M&B40 (M=Be,Mg)

The recent discovery of the all‐boron fullerenes or borospherenes, D_2d B₄₀^?/0, paves the way for borospherene chemistry. Here we report a density functional theory study on the viability of metalloborospherenes: endohedral M@B₄₀ (M=Ca, Sr) and exohedral M&B₄₀ (M=Be, Mg). Extensive global structural searches indicate that Ca@B₄₀ ( 1 , C_2v, ¹A₁) and Sr@B₄₀ ( 3 , D_2d, ¹A₁) possess almost perfect endohedral borospherene structures with a metal atom at the center, while Be&B₄₀ ( 5 , C_s, ¹A′) and Mg&B₄₀ ( 7 , C_s, ¹A′) favor exohedral borospherene geometries with a η⁷‐M atom face‐capping a heptagon on the waist. Metalloborospherenes provide indirect evidence for the robustness of the borospherene structural motif. The metalloborospherenes are characterized as charge‐transfer complexes (M²⁺B₄₀^2?), where an alkaline earth metal atom donates two electrons to the B₄₀ cage. The high stability of endohedral Ca@B₄₀ ( 1 ) and Sr@B₄₀ ( 3 ) is due to the match in size between the host cage and the dopant. Bonding analyses indicate that all 122 valence electrons in the systems are delocalized as σ or π bonds, being distributed evenly on the cage surface, akin to the D_2d B₄₀ borospherene.     

Haloaza‐closo‐dodecaboranes

The bromo‐ and iodoaza‐closo‐dodecaboranes HNB₁₁H₁₀Hal (Hal = Br, I), MeNB₁₁H₉Br₂, and MeNB₁₁H₈Br₃ are formed from [NB₁₁H₁₁]^– and MeNB₁₁H₁₁, respectively, by electrophilic halogenation with elementary halogen in the presence of acidic catalysts. Hydrogen in para‐ or in para‐ and meta‐position with respect to the cluster‐N atom is substituted by halogen. With iodine chloride as halogenation agent, all the 11 boron bound H atoms of MeNB₁₁H₁₁ are substituted to give HNB₁₁Cl₅I₆ with iodine in the para‐ and meta‐ and chlorine in the ortho‐positions, presumably via electrophilic (I) and nucleophilic substitution (Cl). The products are characterized by their NMR spectra, the product HNB₁₁Cl₅I₆ also by crystal structure analysis.     

Properties of halogen atoms for representing intermolecular electrostatic interactions related to halogen bonding and their substituent effects

The electrostatic properties of halogen atoms are studied theoretically in relation to their ability of halogen bonding, which is an attractive intermolecular interaction of a covalently bonded halogen atom with a negatively charged atom of a neighboring molecule. The electric quadrupole (of electronic origin) with a positive zz component Θ_zz of a covalently bonded halogen atom, where the z axis is taken along the covalent bond involving the halogen atom, is mainly responsible for the attractive electrostatic interaction with a negatively charged atom. This positive Θ_zz is an intrinsic property of halogen atoms with the p_x²p_y²p_z configuration of the valence electronic shell, as shown by ab initio molecular orbital calculations for isolated halogen atoms with this electronic configuration, and increases in the order of F < Cl < Br < I, in parallel with the known general sequence of the strength of halogen bonding. For halogen‐containing aromatic compounds, the substituent effects on the electrostatic properties are also studied. It is shown that the magnitude of Θ_zz and the electric field originating from it are rather insensitive to the substituent effect, whereas the electric field originating from atomic partial charges has a large substituent effect. The latter electric field tends to partially cancel the former. The extent of this partial cancellation is reduced in the order of Cl < Br < I and is also reducible by proper substitution on or within the six‐membered ring of halobenzene. Perspectives on the development of potential function parameters applicable to halogen‐bonding systems are also briefly discussed. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010     

Rate constants of reactions of chlorine atoms with aliphatic hydrocarbons and halogen derivatives in the liquid phase

The kinetics of liquid phase chlorination of methane in a difluorodichloromethane medium has been studied in a temperature interval of 293–150 K. The value of activation energy found for the hydrogen abstraction stage by a chlorine atom (E₁) equals 14.2 ± 2.5 kJ/mol, with the processes of chlorine atoms recombination and the cage effect being taken into account. The method of competitive reactions has been employed to assess the constants of reaction of chlorine atoms (k₁) with ethane, propane, hexane, ethylene, allyl bromide, allyl chloride, ethyl chloride, and cyclohexane in nonpolar solvents, viz. difluorodichloromethane and 1,2-dibromotetrafluoroethane. The values (k₁) obtained in the liquid phaseare two to four orders lower than those in the gas phase, while the activation energy is 2–6 kJ/mol higher.     

Investigation of interaction in C60 embedded complexes (X@C60) (X = alkali or halogen) at a series of radial positions by Buckingham potential function

Two typical series of C₆₀ embedded complexes (X@C₆₀) (X = Li, Na, K, Rb, Cs; F, Cl, Br, I) have been chosen to study as prototypes, in which the Buckingham potential (exp-6-1) function was applied to calculating the interactions of the atom pairs. The potential parameters are obtained from related crystals by the simulations using molecular mechanics methods. To utilize the symmetry of the potential field in C₆₀, the calculation is carried out along five typical radial directions. The computational results show that the interaction between the embedded atom and the C₆₀ cage is not purely electrostatic. The repulsive energy, E_rep, accounts for from 0.2% to 6.6% (for the alkali series), and from 1.5% to 58% (for the halogen series); the dispersive energy E_dis accounts for from 1.2% to 6.5% (for the alkali series), and from 2.2% to 42% (for the halogen series); and the electrostatic energy, E_es, accounts for 99% to 87% (for the alkali series) and from 96% to 0% (for the halogen series) when the embedded atom is put at the center of the cage. E_rep reaches up to 8% ∼ 35% (alkali), and 16% ∼ 704% (halogen); E_dis up to 4% ∼ 16% (alkali) and 7% ∼ 26% (halogen); and E_es falls down to about 88% ∼ 49% (alkali), and 96% ∼ 0% (halogen), when the embedded atom deviates 1.8 A from the cage center. The total interactions, E_inter, are all attractive for X (X = Li, Na, K, Rb, Cs; F. Cl, Br), but repulsive for the I atom. It is shown that the potential field in the C₆₀ cage has nearly spherical symmetry in an area with a radius of 1.8 Å around the cage center. The same kinds of interactions for the atoms in the two individual series are compared, and some variation rules are obtained. For (Li@C₆₀), the minimum energy equilibrium point deviates from the center by about 0.5 Å. © 1996 by John Wiley & Sons, Inc.     

Coordination polyhedra PbX<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (X = F,Cl, Br,I) in crystal structures

The Voronoi-Dirichlet polyhedra (VDP) and the intersecting sphere method were used to analyze the coordination of Pb(II) and Pb(IV) atoms by halogen atoms in the crystal structures of 158 compounds. A decrease in the steric effect of the Pb(II) lone electron pair with a decrease in the electronegativity of the surrounding atoms was established. The influence of the nature of the central atom on the steric effect of the lone pair in the structure of the AX _n ^z? complexes, where X is halogen or oxygen, A = Tl(I), Sn(II), Pb(II), As(III),Sb(III), Bi(III), S(IV), Se(IV), Te(IV), or Cl(V) was considered.     

Encapsulation Chalcogen Anions in Perfluorinated Silicon Fullerene: X2−@Si20F20 (X=O,S, Se)

The structures and stabilities of cage Si₂₀F₂₀ and its endohedral complexes X²⁻@Si₂₀F₂₀ (X=O, S, Se) were determined at the B3LYP/6‐31G(d) levels of density functional theory (DFT). It is found that the adiabatic electron affinity (EA_ad) of host cage Si₂₀F₂₀ (I_h) is higher than that of isolated O atom (4.24 vs. 1.46 eV). This suggests the Si₂₀F₂₀ cage can selectively trap and stabilize the capsulated spherical anions. The calculations predict that X=S and Se are nearly located at the center of the cage, and O dramatically deviates from the center in C_3v symmetry. Moreover, the corresponding X²⁻@Si₂₀F₂₀ complexes have more negative inclusion energies (ΔE_inc) and thermodynamic parameters (ΔZ) than X²⁻@C₂₀F₂₀. The amount of charge that is being transferred from the encapsulated anions to the cage increases with the atomic radius, i.e., from O²⁻ (ca. 45%), S²⁻ (ca. 51%) to Se²⁻ (ca. 59%), and such a novel model of cage may have practical uses as potential and electrical building units of nanoscale materials.     

Theoretical study on the smallest endohedral metallofullerenes: TM@C20 (TM = Ce and Gd)

The structure, electronic property, and infrared spectroscopy of endohedral metallofullerenes TM@C₂₀ (TM = Ce and Gd) have been systematically investigated with the aid of the hybrid DFT‐B3LYP functional. It is found that in the endohedral metallofullerenes the average C? C bond lengths are obvious longer than those of empty cage. The frontier orbital analyses show that the endohedral metallofullerene Gd@C₂₀ has the high‐thermodynamic stability. Natural population analysis also tells us that only in the Ce@C₂₀, the Ce atom acts as an electron acceptor with the negative charges, and the 4f orbitals of Ce and Gd atoms have a significant contribution in the formation of chemical bonding. Additionally, the analyses of harmonic vibrational frequencies reveal that when the TM atoms are encapsulated into the C₂₀ cage, the strongest absorption peaks are characterized by a mixture of TM?C bending and C? C stretching vibrations. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Synthesis and properties of polyamides derived from systematically halogenated terephthalic acids with fluorine,chlorine, or bromine atoms

Aromatic polyamides were prepared from systematically halogenated terephthalic acids with hexamethylene diamine, piperazine, 4,4′-diaminodiphenylether and p-phenylene diamine by interfacial or low temperature solution polycondensation. The halogenated terephthalic acids used have mono-, di-, or tetra-substituted fluorine, chlorine, or bromine atoms on the benzene ring. The nonhalogenated terephthalic acid was also used for the comparison. The effects of halogen substitution on the benzene ring on the synthesis and some properties of polymers were examined. Reduced specific viscosity decreased in the order F > Cl > Br by halogen substitution. The incorporation of halogen substituents on the ring led to a decrease of crystallinity and fluoro-substituents hindered the crystallization more strongly. The melting point (T_m) decreased in the order F > Cl > Br by mono-substitution, and Br > Cl > F by di-and tetra-substitution. The change of T_m caused by the difference of the number of halogen substituents differed depending on the rigidity of polymer chains. The flame-retardancy estimated by thermogravimetry, self-ignition, and flash-ignition test increased with increasing halogen content of the polymers. Solubility increased remarkably by halogen substitution. The peak temperature of tan δ decreased by halogen substitution. Some discussion was made on these effects of halogen substitution.     

Novel Copper(I) Clusters with 2‐(Diphenylphosphanyl)anilide Ligands. Synthesis and Crystal Structures of [Cu6X2(NHR)4] (X = Cl,Br, I; R = C6H4‐2‐PPh2)

Treatment of copper(I) halides CuX (X = Cl, Br, I) with lithium 2‐(diphenylphosphanyl)anilide [Li(HL)] in THF led to the formation of hexanuclear copper(I) complexes [Cu₆X₂(HL)₄] [X = Cl ( 1 ), Br ( 2 ), I ( 3 )]. In compounds 1 – 3 , the copper atoms are in a distorted octahedral arrangement and the amide ligands adopt a μ₃‐κP,κ²N bridging mode. Additionally there are two μ₂‐bridging halide ligands. Each of the [Cu₆X₂(HL)₄] clusters comprises two copper atoms, which are surrounded by two amide nitrogen atoms in an almost linear coordination [Cu–N: 186.2(3)–188.0(3) pm] and four copper atoms, which are connected to an amide N atom, a P atom, and a halogen atom in a distorted trigonal planar fashion [Cu–N: 199.6(3)–202.3(3) pm)].     

Borane Derivatives: A New Class of Super‐ and Hyperhalogens

Super‐ and hyperhalogens are a class of highly electronegative species whose electron affinities far exceed those of halogen atoms and are important to the chemical industry as oxidizing agents, biocatalysts, and building blocks of salts. Using the well‐known Wade–Mingos rule for describing the stability of closo‐boranes B_nH_n^2? and state‐of‐the‐art theoretical methods, we show that a new class of super‐ and hyperhalogens, guided by this rule, can be formed by tailoring the size and composition of borane derivatives. Unlike conventional superhalogens, in which a central metal atom is surrounded by halogen atoms, the superhalogens formed according to the Wade–Mingos rule do not have to have either halogen or metal atoms. We demonstrate this by using B₁₂H₁₃ and its isoelectronic cluster CB₁₁H₁₂ as examples. We also show that while conventional superhalogens containing alkali atoms require at least two halogen atoms, a single borane‐like moiety is sufficient to give M(B₁₂H₁₂) clusters (M=Li, Na, K, Rb, Cs) superhalogen properties. In addition, hyperhalogens can be formed by using the above superhalogens as building blocks. Examples include M(B₁₂H₁₃)₂ and M(CB₁₁H₁₂)₂ (M=Li–Cs). This finding opens the door to an untapped source of superhalogens and weakly coordinating anions with potential applications.     

Iodine(III)/AlX3-mediated electrophilic chlorination and bromination of arenes. Dual role of AlX3 (X = Cl,Br) for (PhIO)n depolymerization and as the halogen source

An efficient chlorination and bromination of arenes mediated by in situ-formed PhI(X)OAlX₂ (X = -Cl, -Br), which is proposed as a plausible halogenating species, is described. The proposed dual role displayed by AlX₃, enables the Iodosylbenzene [(PhIO)_n] depolymerization while also acting as the halogen source by transferring the chlorine or bromine atoms to the iodine(III) center. This process allowed the chlorination and bromination of different arenes and heteroarenes under mild and open flask conditions. To the best of our knowledge, this is the first report describing a dual role of aluminum salts applied to the direct C-H chlorination and bromination of arenes.     

Finding all‐nonmetal transition‐metal‐like superatom and its magnetic building block

In novel superatom chemistry, it is very attractive that all‐metal clusters can mimic the behaviors of nonmetal atoms and simple nonmetal molecules. Wizardly all‐metal halogen‐like superatom Al₁₃ with 2P⁵ sub shell (corresponding to the 3p⁵ of chlorine) is the most typical example. In contrast, how to mimic the behaviors of magnetic transition‐metal atom using all‐nonmetal cluster is an intriguing challenge for superatom chemistry. In response to this based on human intuition, using quantum chemistry methods and extending jellium model from metal cluster to all‐nonmetal cluster, we have found out that all‐nonmetal octahedral B₆ cluster with characteristic jellium electron configuration 1S²1P⁶2S²1D⁸ in the triplet ground state can mimic the behaviors of transition‐metal Ni atom with electron configuration 3s²3p⁶4s²3d⁸ in electronic configuration, physics and chemistry. Interestingly, the characteristic order of 1S1P2S1D for the B₆ nonmetal cluster with short B‐B lengths is different from that of the traditional jellium model—1S1P1D2S for metal clusters with long M‐M lengths, which exhibits a novel size effect of nonmetal cluster on jellium orbital ordering. Based on the jellium electron configuration, the B₆ with the spin moment value of 2μ_B is a new all‐nonmetal transition‐metal nickel‐like superatom exhibiting a new kind of all‐nonmetal magnetic superatom. Finding the application of the all‐nonmetal magnetic superatom, we encapsulate the magnetic superatom B₆ inside fully hydrogenated fullerene forming a clathrate B₆@C₆₀H₆₀ with the spin moment value of 2μ_B. As the C₆₀H₆₀ cage as a polymerization unit can conserve the spin moment of endohedral B₆, the clathrate B₆@C₆₀H₆₀ is a new all‐nonmetal magnetic superatom building block. Naturally, magnetic superatom structures of the B₆ and B₆@C₆₀H₆₀ may be metastable.