Halide Counterions Research Articles

Composites of quaternized poly(pyridylacetylene) and silver nanoparticles: Nanocomposite preparation, conductivity and photoinduced patterning

Suspensions containing quaternized poly(pyridylacetylene) (PPyA) and AgX (X = Br and I) were obtained by simply mixing PPyA with water soluble silver salts. The suspensions were stable in the dark at room temperature, and could be cast into uniform films. After exposure to UV-light for sufficient time, Ag nanoparticles were in situ generated in the polymer matrix via photochemical reaction. By adjusting the Ag+ contents and the halide counterions, the size of Ag particles, the conductivity of the composite films, and the surface morphology of the composites were tuned. The quaternized PPyA absorbed UV-light efficiently and the photogenerated halogen caused fast degradation of the polymers. Thus the photo-chemical process concomitantly resulted in the formation of Ag nanoparticles and highly porous films. These properties offer the composite materials potential in the construction of UV-eroding conductive patterns, embedded metal nanostructures, and porous films for loading metal particles as catalyst.

Anion/Cation Layers at Electrified Interfaces: A Comprehensive STM, XRD and XPS Case Study

Charged organic adsorbates play an important role in a number of electrochemical reactions, e.g. as additives for metal plating relevant for device fabrication in the semiconductor industry. Fundamental investigations are mandatory in order to acquire profound knowledge of the structural and electronic properties of these layers parallel and perpendicular to the surface, and to finally achieve a deeper mechanistic understanding of the kinetics of involved charge transfer reactions taking place at these complex metal/organic/electrolyte interfaces. A key structural motif of these interfaces consists in 'paired' (inorganic)anion/(organic)cation layers that can have an enormous stability even during an ongoing charge transfer reaction. In this contribution we present and discuss a selected case study on the co-adsorption of halide anions and cationic organic molecules that exhibit a pronounced redox activity. It will be demonstrated that their phase behavior at the interface crucially depends on both their particular redox-state and the surface concentration of the halide counter ions. The subtle balance between adsorbate–adsorbate and adsorbate–substrate interaction of the poly-cationic organic layer can be carefully controlled by potential dependent anion adsorption and desorption processes through the organic layer. This process can be followed by in situ high-resolution scanning tunnelling microscopy, while additional information about the structural and chemical state of the respective phase is obtained from in situ X-ray diffraction and ex situ photoelectron spectroscopy.

Cationic Conjugated Polyelectrolyte Electron Injection Layers: Effect of Halide Counterions

We examine the influence of halide counteranions on the efficiencies of solution-processed multilayer polymer light-emitting diodes (PLEDs) containing cationic conjugated polyelectrolyte (CPE) electron injection layers (EILs). The parent CPE used in these studies is poly[9,9-bis[6′-(N,N,N-trimethylammonium)hexyl]fluorene-alt-co-1,4-phenylene] bromide. Dialysis was used for exchanging counteranions, while X-ray photoelectron spectroscopy (XPS) provides a convenient technique for evaluating the final polymer composition. The luminous efficiencies of PLEDs with a poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) emissive layer decrease in the order F− > Cl− > Br− > I−. Oxidation of the halide counteranions is likely to occur at the MEH-PPV/CPE interface when the oxidation potential of the counteranion is aligned with the highest occupied molecular orbital of MEH-PPV, that is, Br− and I−. For these heavier halide counteranions, we find that pulsed bias measurements reduce ion migration to t...

Competing reactions of hypercoordinate silicon dichelates

AbstractNeutral hexacoordinate silicon complexes derived from hydrazide chelating ligands with imino‐donor groups, and their pentacoordinate ionic dissociation products, undergo facile intramolecular aldol‐type condensation catalyzed by their chloride counterion leading to formation of a third chelate ring. In analogous silacyclobutane dichelates, in the absence of halide counterion, a similar uncatalyzed rearrangement takes place, accompanied by opening of the four‐membered ring. In the absence of α‐protons necessary for the condensation, the four‐membered ring residue adds directly to one of the imino‐carbon atoms forming a new CC bond and closing a different chelate ring. This latter addition to the imino carbon is the preferred reaction pathway, even in the presence of 12 α‐protons, when cyanide ion replaces the chloride counterion and acts as nucleophile. The cyanide reactivity is rationalized in terms of the HSAB concept. An unusual intramolecular rearrangement involving the migration of a t‐butyl group from silicon to carbon, while enabling the unprecedented attachment of a third hydrazide chelating agent, leading to a hexacoordinate trichelate complex, is presented. Copyright © 2008 John Wiley & Sons, Ltd.

Effect of the Halide Counterion in the ROMP of exo‐Benzyl‐[2‐(3,5‐dioxo‐10‐oxa‐4‐aza‐tricyclo[5.2.1.02,6]dec‐8‐en‐4‐yl)ethyl]dimethyl ammonium Bromide/Chloride

AbstractWe describe results relating to the effect of halide counterion in the ROMP of a permanently cationic exo‐7‐oxanorbornene derivative. Statistical copolymerizations of exo‐benzyl‐[2‐(3,5‐dioxo‐10‐oxa‐4‐aza‐tricyclo[5.2.1.02,6]dec‐8‐en‐4‐yl)ethyl]dimethyl ammonium bromide/chloride were conducted at different molar ratios and the polymerizations evaluated with respect to their kinetic features, as well as their molecular mass profiles, as a function of conversion, and the ability to produce materials with narrow molecular mass distributions. The polymerization characteristics are rationalized in terms of the in situ formation of the mixed Grubbs' derivative RuClBr(PCy3)2CHPh and/or the dibromo analog RuBr2(PCy3)2CHPh.magnified image

Synthesis, Structures, and Stability of N‐Donor‐Stabilized N‐Silylphosphoranimine Cations

A series of DMAP-stabilized (DMAP=4-dimethylaminopyridine) N-silylphosphoranimine cations [DMAPPR(2)==NSiMe(3)](+), bearing R=Cl ([8](+)), Me ([10 a](+)), Me/Ph ([10 b](+)), Ph ([10 c](+)), and OCH(2)CF(3) ([10 d](+)) substituents, have been synthesized from the reactions of the parent phosphoranimines Cl(3)P==NSiMe(3) (3) and XR(2)P==NSiMe(3) (X=Cl (9), Br (11); R=Me (9 a and 11 a), Me/Ph (9 b and 11 b), Ph (9 c and 11 c), and OCH(2)CF(3) (9 d and 11 d)) with DMAP and silver salts as halide abstractors. Reactions in the absence of silver salts yield the corresponding cations, with halide counterions. The stability of the salts is highly dependent on the phosphoranimine substituent and the nature of the counteranion, such that electron-withdrawing substituents and non-coordinating anions yield the most stable salts. X-ray structural determination of the cations reveal extremely short phosphoranimine P--N bond lengths for the cations [8](+) and [10 d](+) (1.47-1.49 A) in which electron-withdrawing substituents are present and a longer phosphoranimine P--N length for the cation [10 a](+) (1.53 A) in which electron-donating substituents are present. Very wide bond angles at nitrogen are observed for the salts containing the cation [10 d](+) (158-166 degrees ) and indicate significant sp hybridization at the nitrogen centre.

Silicon rehybridization and molecular rearrangements in hypercoordinate silicon dichelates

AbstractHydrazide-based hypercoordinate silicon dichelates are remarkably flexible in terms of geometry and reactivity: this paper demonstrates how rather subtle constitutional changes result in dramatic geometrical and reactivity changes. A change of ligand-donor group from NMe2to N=CMe2changes the solid-state geometry from bicapped tetrahedral to octahedral. These two geometries are shown to coexist in solution in dynamic equilibrium. Hexacoordinate complexes are shown to dissociate to pentacoordinate compounds in two distinct ways: ionic or neutral, depending on substitution. Hexacoordinate dichelates with imino-donor groups undergo a skeletal rearrangement (intramolecular aldol-type condensation of imines), catalyzed by their dissociated halide counterions. However, even in the absence of counterions, silacyclobutane dichelates undergo a similar rearrangement.

Do Amphiphile Aggregate Morphologies and Interfacial Compositions Depend Primarily on Interfacial Hydration and Ion-Specific Interactions? The Evidence from Chemical Trapping

Surface-active amphiphiles aggregate spontaneously in water to form association colloids such as micelles, microemulsions, and vesicles. The hydrophobic effect drives aggregation, but the opposing forces that provide balance and determine equilibrium morphologies are not understood, in particular, how specific ion effects, which often follow a Hofmeister series, affect the properties of association colloids. We have harnessed the competitive trapping of arenediazonium ions by weakly basic nucleophiles such as halide counterions, anionic headgroups, alcohols, urea, and water, to estimate their concentrations in the interfacial regions of association colloids from reaction product yields. In the chemical trapping method, product yields are proportional to the concentrations of water and other nucleophiles within the interfacial region, not their stoichiometric concentrations in solution. Changes in the balance of forces controlling aggregate structure are reflected in changes in interfacial concentrations of water and other components in association colloids as reported by the chemical trapping method. Significant changes in interfacial water and counterion concentrations are observed during structural transitions. Specific ion effects on sphere-to-rod transitions of cationic amphiphiles are interpreted in terms of the strengths of headgroup and counterion pairing and ion hydration interactions. Trapping results also provide important information on interfacial compositions of microemulsions, vesicles, nonionic micelles and macroemulsions, reverse micelles, micelles in aqueous urea, and anionic polyelectrolytes. Identifying relationships between aggregate morphology and interfacial composition by chemical trapping has just begun.

Synthesis, Spectroscopic, and Structural Investigation of the Cyclic [N(PR2E)2]+ Cations (E = Se, Te; R = iPr, Ph): the Effect of Anion and R-Group Exchange

Two-electron oxidation of the [N(PiPr2E)2]- anion with iodine produces the cyclic [N(PiPr2E)2]+ (E =Se, Te) cations, which exhibit long E-E bonds in the iodide salts [N(PiPr2Se)2]I (4) and [N(PiPr2Te)2]I (5). The iodide salts 4 and 5 are converted to the ion-separated salts [N(PiPr2Se)2]SbF6 (6) and [N(PiPr2Te)2]SbF6 (7) upon treatment with AgSbF6. Compounds 4-7 were characterized in solution by multinuclear NMR, vibrational, and UV-visible spectroscopy supported by DFT calculations. A structural comparison of salts 4-7 and [N(PiPr2Te)2]Cl (8) confirms that the long E-E bonds in 4, 5, and 8 can be attributed primarily to the donation of electron density from a lone pair of the halide counterion into the E-E sigma* orbital (LUMO) of the cation. The phenyl derivative [N(PPh2Te)2]I (9) was prepared in a similar manner. However, the attempted synthesis of the selenium analogue, [N(PPh2Se)2]I, produced a 1:1 mixture of [N(PPh2Se)2(mu-Se)][I] (10) and [SeP(Ph2)N(Ph2)PI] (11). DFT calculations of the formation energies of 10 and 11 support the observed decomposition. Compound 10 is a centrosymmetric dimer in which two six-membered NP2Se3 rings are bridged by two I- anions. Compound 11 produces the nine-atom chain {[N(PPh2)2Se]2(mu-O)} (12) upon hydrolysis during crystallization. The reaction between [(TMEDA)NaN(PiPr2Se)2] and SeCl2 in a 1:1 molar ratio yields the related acyclic species [SeP(iPr2)N(iPr2)PCl] (13), which was characterized by multinuclear NMR spectroscopy and an X-ray structural determination.

Interaction of cationic surfactants with carboxymethylcellulose in aqueous media

We have examined the polymer–surfactant interaction in mixed solutions of the cationic surfactants, i.e., dodecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, tetradecyltriphenylphosphonium bromide, and tetradecylpyridinium bromide and a semiflexible anionic polyelectrolyte carboxymethylcellulose in water and aqueous salt solutions by various techniques: tensiometry, viscosimetry or ion-selective electrode method, and dynamic light scattering. We have investigated the effect of varying surfactant chain length, head group size, counterion, and ionic strength on the critical aggregation concentration (CAC) of mixed polymer surfactant systems and the collapse of the polymer molecule under different solution conditions. The CAC decreases with increasing alkyl chain length. Above a certain surfactant concentration, mixed aggregates start growing until their macroscopic phase separation. The growth is more rapid with greater surfactant tail length and with increasing head group size. This is attributed in both cases to the increasing hydrophobic interaction between polymer and surfactant. Among surfactants with monovalent halide counterions, iodide induces the strongest binding, reflected by the onset of growth of the mixed aggregates at low surfactant concentration. This is perhaps related to the decreasing hydration of the counterion from chloride to iodide. The surfactant concentration at which the viscosity of the solution starts to decrease sharply is smaller than the CAC, and probably reflects polymer chain shrinkage due to noncooperative binding.

Application of molten salts in hydroalkoxycarbonylation of styrene

Hydroalkoxycarbonylation of styrene using palladium-based catalyst was studied in quaternary ammonium salts as reaction media. Under the reaction conditions applied, the catalyst-containing phase can be reused several times without a significant decrease in activity and selectivity as a function of the precursor and the halide counter ion used.

Bulky Monodentate Phosphoramidites in Palladium‐Catalyzed Allylic Alkylation Reactions: Aspects of Regioselectivity and Enantioselectivity

A series of bulky monodentate phosphoramidite ligands, based on biphenol, BINOL and TADDOL backbones, have been employed in the Pd-catalysed allylic alkylation reaction. Reaction of disodium diethyl 2-methyl malonate with monosubstituted allylic substrates in the presence of palladium complexes of the phosphoramidite ligands proceeds smoothly at room temperature. The regioselectivities observed depend strongly on the leaving group and the geometry of the allylic starting compounds. Mono-coordination occurs when these ligands are ligated in [Pd(allyl)(X)] complexes (allyl=C3H5, 1-CH3C3H4, 1-C6H5C3H4, 1,3-(C6H5)2C3H3; X=Cl, OAc). The solid-state structure determined by X-ray diffraction of [Pd(C3H5)(1)(Cl)] reveals a non-symmetric coordination of the allyl moiety, caused by the stronger trans influence of the phosphoramidite ligand relative to X-. In all of these complexes, the syn,trans isomer is the major species present in solution. Because of fast isomerisation and high reactivity of the syn,cis complex, the major product formed upon alkylation is the linear product, especially for monosubstituted phenylallyl substrates in the presence of halide counterions. In the case of biphenol- and BINOL-based phosphoramidites, however, a strong memory effect is observed when 1-phenyl-2-propenyl acetate is employed as the substrate. In this case, nucleophilic attack competes effectively with the isomerisation of the transient cinnamylpalladium complexes. The asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate afforded the chiral product in up to 93 % ee. Substrates with smaller substituents gave lower enantioselectivities. The observed stereoselectivity is explained in terms of a preferential rotation mechanism, in which the product is formed by attack on one of the isomers of the intermediate [Pd[1,3-(C6H5)2C3H3](L)(OAc)] complex.

Preparation and crystal structure of (2,2 ′-bibenzimidazole)dihalobis(triphenylphospine)rhenium(III) halides

The reaction of ReOX 3(PPh 3) 2 (where X=Cl, Br) with 2,2 ′-bibenzimidazole (bibzimH 2) in the presence of excess PPh 3 yields the rhenium(III) cationic complexes [ReX 2(PPh 3) 2(bibzimH 2)]X, in which the phosphines are trans to one another, whereas the plane perpendicular to this direction includes the chelating bidentate bibzimH 2 and two cis halogen ligands. The third halogen is a halide counter-ion, attached to the complex cation via a pair of N–H⋯X − hydrogen bonds involving the two N–H groups of bibzimH 2. Crystallographic work on the chloro compound indicates that the departure from octahedral geometry is controlled by the bite of the bibzimH 2 ligand and that the presence of the phenylene groups does not introduce substantial steric hindrance. Despite the fact that the species is paramagnetic, the 1H NMR spectra were fully assigned.

Counter-Ion Effects and Interfacial Properties of Aqueous Tetrabutylammonium Halide Solutions

Aqueous solvation of tetrabutylammonium fluoride and iodide was investigated by means of molecular dynamics simulations in extended slab geometry. The varying propensities of the individual ions for the air/water interface were quantified and analyzed in terms of hydrophobic, polarization, and ion–ion interactions. While the cations behave as standard ionic surfactants, the surface behaviour of the halide counter ions strongly depends on the ionic size and polarizability—iodide is surface active, while fluoride is repelled from the interface. The counter-ion effects at different concentrations on the density and charge profiles across the aqueous slab are discussed in detail.

Bicarbonate surfoxidants: micellar oxidations of aryl sulfides with bicarbonate-activated hydrogen peroxide.

The mechanism and kinetics of bicarbonate-catalyzed oxidations of sulfides by H(2)O(2) at the aqueous /cationic micellar interface have been investigated. The general term surfoxidant is introduced to describe the combination of an ionic surfactant with a reactive counterion that is itself an oxidant or activates an oxidant from the bulk solution to form an oxidant counterion. It is shown that the new catalytic cationic surfoxidant CTAHCO(3) (cetyltrimethylammonium bicarbonate) significantly enhances the overall oxidation rates as compared to the addition of bicarbonate salts to CTACl and CTABr, for which the halide counterions must undergo equilibrium displacement by the oxidant anion (peroxymonocarbonate, HCO(4)(-)). General equations based on the classic pseudophase model have been derived to account for the preequilibrium reaction in the aqueous and micellar phases, and the resulting model can be used to describe any micellar reaction with associated preequilibria. Rate constants and relevant equilibrium constants for HCO(4)(-) oxidations of aryl sulfides at micellar surfaces have been estimated for CTAHCO(3), CTACl, and CTABr. The second-order rate constants in the Stern layer (k(2)(m)) for sulfide oxidations by HCO(4)(-) are estimated to be approximately 50-fold (PhSEtOH) and approximately 180-fold (PhSEt) greater than the background rate constant k(m)(0) for oxidation by H(2)O(2) at the micellar surface. The estimated values of k(2)(m) are lower than the corresponding values in water by a factor of 20-70 depending on the substrate, but the high local concentration of the bicarbonate activator in the surfoxidant and the local accumulation of substrate as a result of strong binding to the micelle lead to a net increase in the observed reaction rates. Comparisons of CTAHCO(3)-activated peroxide to other highly reactive oxidants such as peroxymonosulfate (HSO(5)(-)) in aqueous surfactant media suggest a wide variety of potential applications for this green oxidant.

ミセル系におけるキノリン誘導体の蛍光消光（原標題は英語）

The halide-sensitive fluorescence probe, 6-methoxy-N-alkylquinolinium, was prepared to investigate the behavior of counterion dissociation in micellar aqueous solution. Fluorescence was quenched by halide ions based on linear Stern-Volmer plots. The plots indicated a distinct break at cmc of cationic surfactants containing halide counterions. The slope of Stern-Volmer for 6-methoxy-N-ethylquinolinium (MEQ) decreased beyond cmc owing to micellar counterion binding. The quenching efficiency of 6-methoxy-N-dodecylquinolinium (C12MQ) increased significantly beyond cmc with surfactant concentration. The fluorescence of micellar solubilized C12MQ would thus appear to be quenched effectively by halide ions at the micellar surface. These ions were found to function effectively as a quencher in cationic micelle systems, but to have no effect on amphiphilic probe fluorescence in the presence of anionic micelles. Repulsive electrostatic interactions are thus shown to occur between halide ions and anionic micelles containing probes.

Novel heterometallic Cd/Cu complexes prepared using zerovalent copper: control of the nuclearity and structural diversity by halide counterions

Three kinds of CdII/CuII compounds of different nuclearity: tetranuclear [Cd2Cu2I4L4(dmso)2] 1, pentanuclear [Cd2Cu3Br6L4(dmso)2] 2 and hexanuclear [Cd4Cu2Cl6L6(H2O)2] 3, have been synthesised by the reaction of zerovalent copper and cadmium halides with non-aqueous (dmso, CH3CN) solutions of 2-dimethylaminoethanol (HL) in air. The choice of counteranion in the initial cadmium salt provides a useful method of altering the nuclearity and structure of the heterometallic Cd/Cu complexes. Crystallographic investigations reveal that 1 has a centrosymmetric tetranuclear structure with a zig-zag Cd–Cu–Cu–Cd skeleton. The molecular structure of 2 consists of a pentanuclear centrosymmetric core in which four metal atoms are linked together by bridging oxygen atoms of L groups and bromide anions to form a parallelogram Cu–Cd–Cu–Cd centred on the fifth Cu. The hexanuclear complex 3 is made up of two symmetry-related units with triangular CuCd2 cores linked by amino alkoxo bridges, involving cadmium centres of both units.

Density Functional Theory Calculations of Vibrational Circular Dichroism in Transition Metal Complexes: Identification of Solution Conformations and Mode of Chloride Ion Association for (+)-Tris(ethylenediaminato)cobalt(III)

Density functional theory calculations of the vibrational circular dichroism (VCD) spectra of a transition metal complex, (+)-tris(ethylenediaminato)cobalt(III) as a free ion and with associated chloride ions, are reported. By comparison with experimental data obtained in our laboratory in 1986 (Young et al. J. Am. Chem. Soc. 1986, 108, 7255) and new measurements, this study identifies, for the first time, the geometry and absolute configuration of the association complex as Λ-δδδ-Co(en)3Cl2+, in which two chloride ions each associate with three NH bonds along the C3-axis of a D3-symmetry complex. The DFT calculations, carried out with both the LanL2DZ and 6-31G(d)[C, H, N]/Stuttgart ECP [Co] basis sets, predict the energy order of ethylenediamine ring conformations as λλλ < λλδ < λδδ < δδδ for the free (gas phase) Λ-Co(en)33+ ion, an order opposite to that deduced from solution studies. The VCD studies identify the δ-conformation as the most prevalent in solution for halide and sulfate counterions, sugge...

Inhibition of corrosion of steel in produced water of Western Desert crude oil

The corrosion inhibition of steel in water from Western Desert (Egypt) crude oil by nine S-alkyl isothioronium halides was studied using open-circuit potential (OCP) measurements and potentiodynamic polarization tests. The objectives were to determine (a) the effect of chain length of the alkyl groups on the inhibition efficiency, (b) the effect of halide counter ion on the performance of the inhibitor, and (c) to apply a recent developed kinetic-thermodynamic model on the data and compare it with common adsorption isotherms. The number of active sites, binding constant and change of free energy of adsorption were computed for all inhibitors studied. The inhibition efficiency was correlated with the molecular structure of the inhibitors. It was found that each organic molecule replaces more than one adsorbed water molecule from the steel surface. Potentiodynamic polarization curves indicated that the compounds acted as mixed-type inhibitors. The OCP measurements showed that adsorption of S-alkyl isothioronium compounds at the steel surface is through two adsorbed layers.

Neutral and cationic biimidazoledihalogenobis(trimethylphosphine)rhenium(iii) complexes: ion-pairing, acid–base and redox propertiesElectronic supplementary information (ESI) available: details of the structure determination and refinement for compounds 4, 5, 7 and 9·OPPh3. See http://www.rsc.org/suppdata/dt/b1/b103719f/

Cationic Re(III) complexes [ReX2(PMe3)2(biimH2)]X (where biimH2 = 2,2′-biimidazole; X = Cl, Br, I) are prepared by phosphine displacement in the corresponding PPh3 complexes in the presence of excess PMe3. The N–H protons of co-ordinated biimidazole are moderately acidic and the monodeprotonated form [ReX2(PMe3)2(biimH)] is isolated after addition of one equivalent of NaOCH3. Crystal structures determined for two compounds of each series reveal that strong hydrogen bonding takes place between the N–H groups and the halide counter-ion in the cationic complexes, whereas the neutral molecules crystallise as dimeric units tightly associated via two complementary N–H⋯N interactions. The acidities of the two N–H groups of [ReCl2(PMe3)2(biimH2)]+ in CH2Cl2 are estimated from UV-visible spectra and found to correspond approximately to those of formic acid and 3-chlorophenol, respectively. Electrochemical data on the series of PPh3 and PMe3 complexes with the three halides indicate that the redox potentials of both the metal and the counter-ion are affected by ion pairing in solution.