Halogen Cations Research Articles

Effects of various halogen anions and cations of alkali metals on energetics of excess charge recombination in stilbene donor–acceptor capped DNA hairpins

DNA hairpin conjugates with a stilbenedicarboxamide (Sa) hole donor and a stilbenediether (Sd) hole acceptor are considered as model systems for studying charge recombination (CR) of excess charges in DNA. Using the method of thermodynamic integration, we estimated the relative free energies of this process in hairpins with three adenine:thymine pairs between Sa and Sd surrounded by 1 M aqueous solutions of ionic compounds M(+)Cl(-) (M = Li, Na, K) and Na(+)X(-) (X = F, Cl, Br, I). The values of this quantity were calculated with respect to the free energy for the same hairpin in the 1 M NaCl aqueous solution. Based on the results obtained, we conclude that halogen anions have no significant influence on the rate of the CR reaction. By contrast, cations of other alkali metals can considerably change the potential barrier of the process, thus affecting the reaction rate. Different results obtained for cations and anions were attributed to the fundamental distinction in the electrostatic interactions of M(+) and X(-) species with negatively charged phosphate groups of the hairpin. In addition, our results show that the relative free energy of CR is larger for cations that are able to be closer to Sd and Sa structural units. The latter correlation suggests that the replacement of Na(+) by cations of other alkali metals enables one to change the CR rate modifying it in either direction.

Solid-state synthesis of mixed trihalides via reversible absorption of dihalogens by non porous onium salts

1,6-Bis(trimethylammonium)hexane bis(trihalides) and mixed bis(trihalides) have been synthesized by treating the corresponding dihydrated halides with molecular dihalogens under gas–solid and solution conditions. Despite the starting halides being non-porous, the trihalide syntheses occur homogeneously, in quantitative yields, and reversibly. In all cases halogen bond prevails over hydrogen bond, dihalogens substitute for the hydration water of starting halide anions and trihalides are formed. The stability of the obtained trihalides is mainly due to cooperative halogen bond and cation templation effect. Hexamethonium halides are proven effective solids for the clathration and storage of molecular dihalogens. While the starting salts are not isostructural, all the formed trihalides and mixed trihalides are isostructural.

ChemInform Abstract: Electrophilic Bromination of Phenol Ethers in Superacid Solution Using Alkali Bromide.

Abstract Electrophilic aromatic bromination of phenol ethers in superacid medium can be achieved with sodium or potassium bromide. The yield and selectivity are lower than with bromine, the oxidation of the halide to the electrophilic halogen cation is obtained by concomitant reduction of antimony pentafluoride. Selectivity is observed only in methylanisole.

A Computational and Experimental Study of the Structures and Raman and 77Se NMR Spectra of SeX3+ and SeX2 (X = Cl, Br, I): FT-Raman Spectrum of (SeI3)[AsF6

The ability of MP2, B3PW91 and PBE0 methods to produce reliable predictions in structural and spectroscopic properties of small selenium-halogen molecules and cations has been demonstrated by using 6-311G(d) and cc-pVTZ basis sets. Optimized structures and vibrational frequencies agree closely with the experimental information, where available. Raman intensities are also well reproduced at all levels of theory. Calculated GIAO isotropic shielding tensors yield a reasonable linear correlation with the experimental chemical shift data at each level of theory. The largest deviations between calculated and experimental chemical shifts are found for selenium-iodine species. The agreement between observed and calculated chemical shifts for selenium-iodine species can be improved by inclusion of relativistic effects using the ZORA method. The best results are achieved by adding spin-orbit correction terms from ZORA calculations to nonrelativistic GIAO isotropic shielding tensors. The calculated isotropic shielding tensors can be utilized in the spectroscopic assignment of the 77Se chemical shifts of novel selenium-halogen molecules and cations. The experimental FT-Raman spectra of (SeI3)[AsF6] in the solid state and in SO2(l) solution are also reported.

Preparation of stable AsBr4+and I2As–PI3+salts. Why didn't we succeed to prepare AsI4+and As2X5+? A combined experimental and theoretical study

In analogy to our successful "PX2+" insertion reactions, an "AsX2+" insertion route was explored to obtain new arsenic halogen cations. Two new salts were prepared: AsBr4+[Al(OR)4]-, starting from AsBr3, Br2 and Ag[Al(OR)4], and I2As-PI3+[Al(OR)]4 from AsI3, PI3 and Ag[Al(OR)4](R=C(CF3)3). The first cation is formally a product of an "AsBr2+" insertion into the Br2 molecule and the latter clearly a "PI2+" insertion into the As-I bond of the AsI3 molecule. Both compounds were characterized by IR and NMR spectroscopy, the first also by its X-ray structure. Reactions of Ag[Al(OR)4] with AsI3 do not lead to ionization and AgI formation but rather lead to a marginally stable Ag(AsI3)2+[Al(OR)]4 salt. Despite many attempts we failed to prepare other PX-cation analogues such as AsI4+, As2X5+ and P4AsX2+(X=Br, I). To explain these negative results the thermodynamics of the formation of EX2+, EX4+ and E2X5+(E = As, P; X = Br, I) was carefully analyzed with MP2/TZVPP calculations and inclusion of entropy and solvation effects. We show that As2Br5+ is in very rapid equilibrium with AsBr2+ and AsBr3(DeltaGo((CH2Cl2))=+30 kJ mol(-1)). The extremely reactive AsBr2+ cation available in the equilibrium accounts for the observed decomposition of the [Al(OR)4]- anion. By contrast, the stability of AsI3 against Ag[Al(OR)4] appears to be kinetic and, if prepared by a suitable route, As2I5+ would be expected to have a stability intermediate between the known P2I5+ and P2Br5+.

Halogen Cation Induced Stereoselective Semipinacol‐Type Rearrangement of Allylic Alcohols: A Highly Efficient Approach to α‐Quaternary β‐Haloketo Compounds.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Halogen Cation Induced StereoselectiveSemipinacol-type Rearrangement of Allylic Alcohols: A Highly EfficientApproach to α-Quaternary β-Haloketo Compounds

Allylic alcohols were found to undergo a semipinacol-type rearrangement induced by halogen cation generated from the chloramine-T/ZnX2 combination, which provided a highly efficient and stereoselective method for the preparation of α-quaternary β-haloketo compounds. This reaction is valuable and versatile since a quaternary carbon could be constructed effectively and three kinds of β-haloketo compounds (X = Cl, Br, I) could be achieved readily.

The Carbonyl Chlorine(I) Cation [ClCO]+ .

The first carbonyl halogen cation in the condensed phase, the superelectrophilic [ClCO]+ ion, has been clearly and unambiguously established by its complete, fully assigned vibrational spectrum. The cation is obtained by the reaction of COCl2 with SbF5 at room temperature in the form of a suspension, in which it is stabilized by oligomeric fluoroantimonate ions.

Multiplication of electronic excitations and formation of radiation defects in alkali halides

The spectrum of F center creation has been measured for KBr:Tl using synchrotron radiation (12–32 eV). The creation efficiency of a stable F center is especially high at 15–17 and 28–30 eV where the absorption of one photon leads to the formation either both of an electron-hole pair and an exciton or two electron-hole pairs and an exciton. In these cases there are favourable conditions for stabilization of mobile radiation defects due to the association of interstitial halogen atoms, holes and cation vacancies.

Creation of stable Frenkel defects by vacuum uv radiation in KBr crystals under conditions of multiplication of electronic excitations.

The spectrum of F-center creation has been measured for KBr:Tl by means of synchrotron radiation (12--24 eV). Analysis of the spectrum reveals the decay of cation excitons (19.7--20.3 eV) with the formation of a double amount of electron-hole pairs. The creation efficiency of a stable F center is especially high at 15--17 eV where the absorption of one photon leads to the formation both of an electron-hole pair and an exciton. In this case there are favorable conditions for stabilization of mobile radiation defects due to the association of interstitial halogen atoms, holes, and cation vacancies.

Preparation and structure of Te4N2Cl8(AsF6)2·2SO2containing Te4N2Cl82+, the first tellurium–nitrogen–halogen cation

The reaction Of TeCl4 and N(SiMe3)3, followed by the addition of AsF5 gives Te4N2Cl8(AsF6)2·2SO2, shown by its X-ray crystal structure to contain Te4N2Cl82+([(Cl3Te)[graphic omitted]Te(Cl)]2+), the first tellurium–nitrogen–halogen cation.

AB initio MO study of the halogen cation basicities of some organic bases

AbstractHartree—Fock calculations were performed to investigate the structure and relative stabilities of complexes between halogen cations and first‐ and second‐row bases. It is shown by means of both a qualitative perturbation molecular orbital treatment and a topological analysis of the electronic charge density that second‐row bases present enhanced halogen cation basicities compared with first‐row bases. In this respect the results predict that although the fluorine cation basicity of water is smaller than its proton affinity, the fluorine cation basicities of SH2, thioether, phosphine and trimethylphosphine are considerably higher than their proton basicities. Similarly, phosphine and trimethylphosphine should have chlorine cation basicities greater than their proton affinities, in contrast with ammonia and trimethylamine. The results also show that fluorine and chlorine cation basicities are more sensitive to methyl substitution than proton affinities.

ChemInform Abstract: Energies and Properties of Ions Involved in Electrophilic Halogenations: Singlet and Triplet States of Halogen Cations (X+, X+ 3, and X2+ 4) and Hydrohalonium Ions (HX+ 2 and H2X+)

ChemInform Abstract: Energies and Properties of Ions Involved in Electrophilic Halogenations: Singlet and Triplet States of Halogen Cations (X+, X+ 3, and X2+ 4) and Hydrohalonium Ions (HX+ 2 and H2X+)

Energies and properties of ions involved in electrophilic halogenations: singlet and triplet states of halogen cations (X+, X3+, and X42+) and hydrohalonium ions (HX2+ and H2X+)

Energies and properties of ions involved in electrophilic halogenations: singlet and triplet states of halogen cations (X+, X3+, and X42+) and hydrohalonium ions (HX2+ and H2X+)

Electrophilic bromination of phenol ethers in superacid solution using alkali bromide

Electrophilic aromatic bromination of phenol ethers in superacid medium can be achieved with sodium or potassium bromide. The yield and selectivity are lower than with bromine, the oxidation of the halide to the electrophilic halogen cation is obtained by concomitant reduction of antimony pentafluoride. Selectivity is observed only in methylanisole.

Oxidation of Indigo Carmine by N-Haloarenesulfonamidates: A Kinetic Study

Abstract Kinetics of oxidation of indigo carmine (IC) by sodium N-haloarenesulfonamidates (RNXNa, where R=CH3C6H4SO2− or C6H5SO2− and X=Cl or Br) chloramine T (CAT), bromamine T (BAT), chloramine B (CAB), and bromamine B (BAB) in alkaline buffer (pH 9–11) has been followed spectrophotometrically at λmax=610 nm. Rate law, –d[IC]/dt=k[OX]0[IC]0[OH−]x where x<1, is obeyed. The reaction products, benzenesulfonamide and toluenesulfonamide retard the rate. Sulfonated anthranilic acid formed was quantitatively determined. Variation of ionic strength or dielectric constant of medium and addition of halide ions have no effect on the reaction. A two pathway mechanism is proposed in which the hypohalous acid (HOX) and the anion of N-haloamine RNX− interact with the substrate in rate limiting steps. The rate increases in the order: BAT>BAB>CAT>CAB, which is attributed to the difference in electrophilicities of halogen cations Br+ and Cl+ involved in the oxidation process and the ease with which these species are formed in reactions.

Extension of AM1 to the halogens

AM1 parameters are reported for the halogens (F,Cl,Br,I). Results for a large number of halogen-containing organic molecules agree well with experiment, the agreement being generally better than for MNDO. The mean AM1 errors in heats of formation and other properties are now similar to those for compounds containing only the “organic” elements (C,H,O,N) and intermolecular interactions are now reproduced in a reasonable manner. While it is an improvement over MNDO, AM1 fails in the case of hypervalent compounds and it also underestimates the stabilities of π complexes derived from halogen cations.

The preparation of SeI3SbF6 and TeI3SbF6; the X-ray crystal structures of SBr3AsF6, SeI3AsF6, SeI3SbF6, and TeI3SbF6; some considerations of the energetics of the formation of SBr3AsF6 and SeI3AsF6

The crystal structures of the compounds SBr3AsF6 (1), SeI3AsF6 (2), SeI3SbF6 (3), and TeI3SbF6 (4) are reported and the quantitative preparation of the hitherto unknown 3 and 4 from SbF5 and the respective elements in SO2 are given. Crystal data are as follows: 1, monoclinic, space group P21/c, with a = 8.015(1) Å, b = 9.342(1) Å, c = 12.126(2), β = 97.81(1)°, and Z = 4; 2, monoclinic, space group P21/c, with a = 8.380(2) Å, b = 10.237(1) Å, c = 12.524(1) Å, β = 99.36(1)°, and Z = 4; 3, monoclinic, space group P21/c, with a = 8.548(2) Å, b = 10.297(6) Å, c = 12.877(8) Å, β = 98.70(3)°, and Z = 4; 4, monoclinic, space group P21/c, with a = 8.463(1) Å, b = 10.676(2) Å, c = 13.121(4) Å, β = 100.05(1), and Z = 4. Compounds 1, 2, 3, and 4 are isostructural and were refined to a final R values of 0.040, 0.051, 0.047, and 0.037, respectively. The structures of these salts consist of essentially discrete MX3+ cations and M′F6− anions (M = S, Se, Te; X = Br, I; M′ = As, Sb) with some cation–anion interactions. TheSeI3+ bond distances and angles were essentially identical in both AsF6− and SbF6− salts (average Se—I distance and I—Se—I angle for AsF6− salt; 2.508(2) Å, 102.4(1)° and for SbF6− salt; 2.512(1) Å, 102.3(1)°). Similarly the average Te—I bond distance and I—Te—I angle for TeI3SbF6 were 2.666(1) Å and 99.8(1)° which are essentially identical to those in the previously reported TeI3AsF6. The average S—Br distance and Br—S—Br angle were 2.142(6) Å and 103.4(2)° in SBr3AsF6. Estimates of the S—I bond distance and I—S—I bond angle in the as yet unknown SI3M′F6 are made from the extrapolation of MX3+ data. The bond distances observed in the simple MX3+ cations (M = S, Se, Te; X = Cl, Br, I) with anions of very low basicity are within 0.02 Å of the corresponding distances calculated by the Schomaker–Stevenson equation. The observed and estimated bond distances in SBr3+, SI3+, and SeI3+ are significantly longer than the corresponding S—Br, S—I, and Se—I distances in S7I+, S7Br+, and Se6I22+. This observation is used to support the thesis that the long intra-cationic halogen–chalcogen contacts in polychalcogen–halogen cations are weakly bonding, and responsible for the cluster-like nature of these cations. The heats of formation of 1 and 2 from their respective elements and AsF5 were estimated.

Collisional and unimolecular ionisation of monatomic halogen cations

Charge-stripping processes of monatomic halogen cations F +, Cl +, Br + and I + having keV translational energies were investigated, and found to closely resemble those of the isoelectronic dications of the noble gases. In the absence of collision gas, an ionisation process is still observed which cannot be attributed to charge-stripping collisions of very high cross-section with background gas molecules, nor to surface interactions, nor to field ionisation. The observed time-dependence of the yield from this collision-free process is, however, also difficult to reconcile with an interpretation in terms of autoionisation of some highly excited metastable state. In addition, the appearance energy of the states involved was found to lie within 1– eV of the ionisation onset. A mechanism was proposed which can account qualitatively for these observations. The crucial step in this proposal involves excitation of Rydberg states by ambient (300 K) black-body radiation, a phenomenon well established for neutral atoms.

Lifetimes of F 2+ and Cl 2+ in the A 2Π u state

The PIFCO technique,in which mass-selected photoion-fluorescence photon coincidences are counted, is used to determine the lifetime of the A 2Π u state of F 2 + and Cl 2 +. Values of 1.4 μs (F 2 +) and 0.54 μs (Cl 2 +) are measured, and they are compared with lifetime measurements by other methods. The F 2 + result is used to determine the electronic transition moment R e of the A 2Π u-X 2Π g transition to be 0.51 au, in excellent agreement with ab initio calculations. Oscillator strengths of the A-X transitions of all fluorescing halogen cations are evaluated, and the results discussed.