Large Counter Anions Research Articles

Flexible Co(II)-and Ni(II)-Based Cationic 2D Metal–Organic Frameworks Based on a Charge-Neutral (O,O)-Donor Bridge

Two new metal–organic frameworks based on highly flexible 1,4-diazabicyclo[2.2.2]octane N,N′-dioxide (odabco) ligands were successfully synthesized and characterized. Their crystallographic formulae are [M(DMF)2(odabco)2](ClO4)2·dioxane, where M2+ = Co2+ (1) and Ni2+ (2), and DMF is N,N-dimethylformamide. The title compounds possess cationic 2D coordination networks filled with perchlorate anions and dioxane solvent molecules in the interlayer space, with 20% solvent accessible volume. Carbon dioxide adsorption measurements for desolvated samples 1a and 2a gave 511 m2/g and 377 m2/g specific surface areas, respectively, revealing the first example of gas adsorption properties in the structure based on a flexible odabco bridge, despite the presence of large counteranions within the positively charged network. Magnetization measurements for 1, 1a, 2 and 2a reveal their paramagnetic nature to be in a reasonable agreement with crystal structures, and almost no solvent dependence of the magnetization characteristics. A decrease in the effective magnetic moment observed at low temperatures is attributed mostly to zero-field level-splitting in the octahedral Ni2+ and Co2+ ions.

Phenanthroline-based Ni(II) coordination compounds involving unconventional discrete fumarate-water-nitrate clusters and energetically significant cooperative ternary π-stacked assemblies: Antiproliferative evaluation and theoretical studies

Two new Ni(II) coordination complexes involving fumarate and 1,10-phenathroline viz.; [Ni2(phen)2(µ-fum)(H2O)6](fum)·6H2O (1) and [Ni(phen)2(H2O)2](0.5 fum)(NO3)·4H2O (2) (fum = fumarate, phen = 1,10-phenanthroline) have been isolated in aqueous medium at room temperature. Crystal structure analyses of the compounds reveal the presence of cooperative (π–π)2/(π–π)1/(π–π)2 stacked ternary assemblies which provide stabilities to the layered architectures. The lattice water and the large counter anions in the lattice of the compounds are involved in the formation of unconventional discrete cyclic fumarate-water, fumarate-water-nitrate clusters and infinite nitrate-water 1D chains that are very scarcely reported in the literature. The energetically significant π-stacked dimers observed in the biologically relevant ternary assemblies of the crystal structures are further studied theoretically using DFT calculations and NCI plot index computational tools. DFT calculations reveal that the cooperative (π–π)2 binding mode of compound 1 is energetically more significant than (π–π)1 Moreover, the study also reveals that for the equivalent cooperative (π–π)1 stacking interactions in both the structures, the energy is unexpectedly higher for compound 2 than that observed for compound 1. Both the compounds induce significant cytotoxicity in Dalton's lymphoma (DL) cancer cells by inducing apoptotic cell death with negligible cytotoxicity in normal cells. Decrease in the mitochondrial membrane potential (MMP) of DL cells after treatment with the compounds also corroborates the apoptotic cell death. The molecular docking and pharmacophore features reveal that the compounds interact and accommodated well with the active sites of anti-apoptotic proteins.

Polypyrrole-coated carbon fibre electrodes for paracetamol and clozapine drug sensing

Polypyrrole (PPy) fibre electrodes were studied to determine their ability to sense paracetamol (as a model drug) in the presence of the interferents dopamine and ascorbic acid. PPy was electropolymerised onto carbon fibres using cyclic voltammetry in the presence of two different counter anions: sodium dodecyl sulfate (SDS) and potassium nitrate (KNO3). The surface of the PPy.SDS and PPy.KNO3 fibre electrodes was characterised using Raman spectroscopy and scanning electron microscopy. The PPy.SDS-coated carbon fibre had a 14-fold larger electrochemical surface area compared to a bare carbon fibre (calculated using the Randles-Sevcik equation). The use of a large counter anion as dopant (dodecyl sulfate) produced fibres with a greater drug sensing response (cf. the use of smaller nitrate anion). The use of the PPy.SDS fibre electrode in differential pulse voltammetry (DPV) allowed sensing of paracetamol with a detection limit (3σ S/N) of 34 µM. For the anodic peak current (0.5 V vs. Ag/AgCl), a linear response range was observed for 50–500 µM. At a paracetamol concentration of 100 µM, the DPV anodic peak current (at 0.5 V vs. Ag/AgCl) was unaffected by the addition of interferents: 100 µM dopamine and 100 µM ascorbic acid. A real-world application of drug sensing was trialled with the anti-psychotic medication clozapine; where the PPy.SDS carbon fibre could sense clozapine with a detection limit of (3σ S/N) of 6 µM and a sensitivity of 15 μA cm−2 μmol−1 L.

Anion-mediated encapsulation-induced emission enhancement of an IrIII complex within a resorcin[4]arene hexameric capsule.

Understanding of encapsulation processes in confined inner spaces of self-assembled hosts is important for the rational creation of supramolecular systems showing unusual reactivities and physical properties through molecular recognition. Herein we report the formation of luminescent supramolecular host-guest complexes consisting of a hydrogen-bonded resorcin[4]arene hexameric capsule and a variety of emissive Ir complex salts. The Ir complexes, accompanied by small counter anions (Cl-, Br-, NO2-, I- and NO3-), are trapped effectively to show large encapsulation-induced emission enhancement (EIEE) behavior, while Ir complexes having large counter anions (ClO4-, PF6- and OTf-) are not stabilized within the capsule, suggesting that the Ir complex cation is trapped together with its counter anion to form an ion-pair in the capsule. Hydrogen-bonding capabilities of the counter anions also contribute to stabilize host-guest association, because the counter anions trapped within the capsule were in contact with the hydrophilic surfaces of the capsule.

Construction and anion exchange of silver(I) complexes bearing 1,2,3-tris(isonicotinoyloxy)benzene

A new potentially tridentate ligand 1,2,3-tris(isonicotinoyloxy)benzene (L) was prepared, and its coordination chemistry with various silver(I) salts AgX (X− = BF4−, ClO4−, PF6−, and CF3SO3−) was investigated in order to elucidate the effects of counteranion size. Self-assembly of silver(I) salts with L afforded four complexes with 1:1 stoichiometries. The molecular structures with small counteranions (BF4−, ClO4−, and PF6−) showed 2-D networks whereas those with large counteranions (CF3SO3−) showed a 1-D network. These silver(I) compounds were fully characterized by infrared spectroscopy, elemental and thermal analyses, and single crystal X-ray diffraction. The role of the present counteranions in determining the structural motifs is discussed in these pages.

Synthesis of Phosphaphenalenium Salts via P–C Reductive Elimination at a Ru(II) Center and Their Fluorescence Properties

Abstract Rare examples of P–C reductive elimination at a Ru(II) center to form phosphonium salts have been developed. A five-membered phospharuthenacycle derived from P(1-Naph)Ph2 and [(η6-C6Me6)RuCl2]2 is converted to η4-phosphaphenalenium complexes [(η6-C6Me6)Ru(η4-phosphaphenalenium)][BArF4] via alkyne insertion followed by P–C reductive elimination. This reaction sequence including P–C reductive elimination is applicable to various dialkyl and diarylalkynes, although the η4-phosphaphenalenium complexes with electron-rich aryl groups are not stable enough to be isolated. The reaction of the η4-phosphaphenalenium complexes with I2, CO or CuCl2 resulted in the liberation of the phosphaphenalenium salts. In contrast to the highly distorted phosphacycle in the Ru complex, the phosphaphenalenium cations have nearly planar π-conjugated structure, and their BArF4 salts display green to yellow and blue to green fluorescence in solution and in the solid state, respectively, depending on the substituents on the phenalene skeleton. Because of the cationic character of the phosphacycle as well as their large counteranion, π–π stacking of the phosphacycles in the crystalline state is effectively suppressed, leading to emission with shorter wavelength in the solid state than in solution. Electronic structures of phosphaphenalenium ions as well as effects of substituents were investigated by TD-DFT calculations.

The effect of the counteranion on the loss of hydrogen from cationic ruthenium dihydrogen complexes in the solid state

The loss of the dihydrogen ligand from trans-[Ru(H2)H(dppe)2]+ cations (dppe = PPh2CH2CH2PPh2) in the solid state was investigated using 31P CP/MAS NMR spectroscopy and single crystal X-ray diffraction. While facile dihydrogen loss was observed at room temperature from crystalline samples with the large counteranions BPh4− and B(ArF)4−, ArF = 3,5-C6H3(CF3)2, it only occurred upon heating from complexes with the smaller anions BF4− and PF6−, resulting in the loss of crystallinity. Single crystal X-ray diffraction studies of the new complexes [RuH(dppe)2]BPh4 and trans-[Ru(H2)H(dppe)2]BArF4 are reported. A comparison of the crystal structures of square pyramidal [RuH(dppe)2]BPh4 and octahedral [Ru(H2)H(dppe)2]BPh4 shows that only minor structural changes occur upon loss of H2 from the crystal.

Polypyrrole doped with dodecyl benzene sulfonate electrodeposited on carbon fibers for flexible capacitors with high-performance

Polypyrrole (PPy) doped with large counter anion of dodecyl benzene sulfonate (DBS) has been electrodeposited on carbon fibers to obtain the composite of PPy/DBS/CF, and the preparation conditions for the flexible composites have also been optimized. The microstructures of PPy/DBS/CF composites are observed by scanning electron microscope, and the electrochemical properties of the composites are investigated by using electrochemical techniques. The flexible wire-shaped electrochemical capacitors can be fabricated conveniently by using the composites of PPy/DBS/CF as electrodes, and the performances of the flexible capacitors are evaluated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy methods in different polyvinyl alcohol (PVA)-based gel electrolytes. The results show that the electrolytes have significant influence on the capacitors’ performances. The specific capacitance of PPy/DBS/CF can reach to about 29.0mFcm−1 when LiClO4/PVA and LiCl/PVA are used as electrolytes. The energy density and power density of the capacitors based on LiCl/PVA electrolyte can get 1.20mWhcm−3 and 0.59Wcm−3 at discharge current density of 1.50Acm−3. Furthermore, the flexible capacitors based on LiCl/PVA electrolyte have excellent cyclic stability, which can retain 90.5 % of the initial capacitance after 5000 cycles, while the capacitors based on LiClO4/PVA only retains about 80.1 % of their initial capacitance.

Corrosion of conductive polypyrrole: Effects of environmental factors, electrochemical stimulation, and doping anions

The effects of environmental factors, electrochemical stimulation, and doping anions on the corrosion behaviour of conductive polypyrrole (PPy) films in alkaline aqueous media were studied with cyclic voltammetry, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. High concentrations of electrolyte, low dissolved oxygen and low temperatures enhance the stability of PPy. Polarising PPy at a negative potential inhibits its corrosion obviously. PPy doped with large counter anions shows better corrosion resistance than PPy doped with small counter ions. The possible mechanism involved in PPy corrosion process is discussed.

Vapochromic and Mechanochromic Tetrahedral Gold(I) Complexes Based on the 1,2‐Bis(diphenylphosphino)benzene Ligand

Tetrahedral gold(I) complexes containing the diphosphane ligand (dppb=1,2-bis(diphenylphosphino)benzene), [Au(dppb)(2)]X [X=Cl (1), Br (2), I (3), NO(3) (4), BF(4) (5), PF(6) (6), B(C(6)H(4)F-4)(4) (7)], and the ethanol and methanol adducts of complex 4, 8, and 9, were prepared to analyze their unique photophysical properties. These complexes are classified into two categories on the basis of their crystal structures. In Category I, the complexes (1-5) have relatively-small counter anions and two dppb ligands are symmetrically coordinated to the central Au(I) atom, and display an intense blue phosphorescence. Alternatively, the complexes (6-9) in Category II have large counter anions and two dppb ligands asymmetrically coordinated to Au(I) atom, and display a yellow or yellow orange phosphorescence. The difference in the phosphorescence color of the complexes between the Category I and II is ascribed to the change in the structure of the cationic moiety in the complex. According to DFT calculations, the symmetry reduction caused by the large counter anion of the complex in Category II gives the destabilization of HOMO (σ*) levels, leading to the red-shift of the emission peak. We have demonstrated that the symmetry reductions are responsible for the phosphorescence color alteration caused by external stimuli (volatile organic compounds and mechanical grinding).

Exchange of counter anions in electropolymerized polyaniline films

Mobile counter anion exchange of electropolymerized polyaniline (PANI) films with the anions in acid solutions has been investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy, Raman, UV–vis, and fluorescence spectra. The studied acids include camphorsulfonic acid, p-toluene sulfonic acid, HCl, HClO4, H2SO4 and H3PO4. In two cases of small and large counter ions of PANI films, CV tests have been performed alternately three times in each of two electrolytes containing organic or inorganic acid. The investigation of electrochemical and spectrophotometric measurements reveals that large counter anions can be easily replaced by the small anions; and the reverse exchange also occurs, but shows very low efficiency. This indicates that the achieved anion exchange in both cases leads to the remarkable alteration in electrochemical behavior and electrical conductance of PANI films. This implies counter anions, whatever the original or redoping ones, play an important role in the electrical, electrochemical, even optical properties of PANI. However, the polymer morphology does not be changed after exchange tests. This allows us to point out a ‘morphology-memory’ effect which is very significant for the development and application of PANI films with the same morphology and different properties.

EC-AFM investigation of reversible volume changes with electrode potential in polyaniline

The volume changes in electrochemically deposited polyaniline (PANI) on highly oriented pyrolytic graphite (HOPG) in S O 4 2 - and Cl − medium along with PANI microtubules and nanowires in S O 4 2 - medium were investigated by electrochemical atomic force microscopy (EC-AFM). Volume expansion was observed in the oxidized state with contraction in the reduced state due to the movement of solvated anions inside the polymer matrix during the oxidation process and its expulsion during the reduction process. Reversible volume changes with changing electrochemical potential were observed in case of microtubules and nanowires. To observe the effect of large counter anion, EC-AFM studies of volume changes with electrode potential in polyaniline modified with poly(styrene sulfonate) (PANI–PSS) nanowires were performed in S O 4 2 - medium. The changes were found to be more than 33% and in the reverse direction in this case due to presence of larger immobile PSS anion in the polymer matrix with volume changes predominantly due to movement of solvated H + ions inside the polymer matrix during the reduction process. To further support our observations we performed the in situ electrochemical synthesis of PANI nanoparticles on HOPG inside AFM electrochemical cell and monitored its volume changes with electrode potential using EC-AFM. The volume changes in these nanoparticles could be clearly observed with variation in percentage changes between 17.5% and 89.8%.

Supramolecular Assemblies Obtained by Large Counteranion Incorporation in a Well-Oriented Polycationic Copolymer

The anodic oxidation of a two bipyridiniums meso-substituted octaethylporphyrin leads to the coating of the working electrode by a cationic polymeric film. Description of the formation and morphological properties of this conducting film are presented along with the electrochemical synthesis of the initial porphyrinic subunit used as monomer for the electropolymerization. We investigated the effects of the counteranion on the morphology of the copolymer 2-poly-Zn where the initial regular arrangement of swollen coils aggregated in the form of "peanuts" all oriented in the same direction was strongly modified in the gain of a new still well oriented supramolecular structure.

Layer‐by‐Layer Deposition of Rhenium‐Containing Hyperbranched Polymers and Fabrication of Photovoltaic Cells

Multilayer thin films were prepared by the layer-by-layer (LBL) deposition method using a rhenium-containing hyperbranched polymer and poly[2-(3-thienyl)ethoxy-4-butylsulfonate] (PTEBS). The radii of gyration of the hyperbranched polymer in solutions with different salt concentrations were measured by laser light scattering. A significant decrease in molecular size was observed when sodium trifluoromethanesulfonate was used as the electrolyte. The conditions of preparing the multilayer thin films by LBL deposition were studied. The growth of the multilayer films was monitored by absorption spectroscopy and spectroscopic ellipsometry, and the surface morphologies of the resulting films were studied by atomic force microscopy. When the pH of a PTEBS solution was kept at 6 and in the presence of salt, polymer films with maximum thickness were obtained. The multilayer films were also fabricated into photovoltaic cells and their photocurrent responses were measured upon irradiation with simulated air mass (AM) 1.5 solar light. The open-circuit voltage, short-circuit current, fill factor, and power conversion efficiency of the devices were 1.2 V, 27.1 mu A cm(-2), 0.19, and 6.1x10(-3) %, respectively. The high open-circuit voltage was attributed to the difference in the HOMO level of the PTEBS donor and the LUMO level of the hyperbranched polymer acceptor. A plot of incident photon-to-electron conversion efficiency versus wavelength also suggests that the PTEBS/hyperbranched polymer junction is involved in the photosensitization process, in which a maximum was observed at approximately 420 nm. The relatively high capacitance, determined from the measured photocurrent rise and decay profiles, can be attributed to the presence of large counter anions in the polymer film.

Surface-functionalized nanoparticles with liquid-like behavior: The role of the constituent components

Ionically modified silica nanoparticles with large counter anions (sulfonate, isostearate) at two silica volume fractions (13 and 27%) form a viscous fluid and a glass but not crystalline solids. Dielectric spectroscopy, Brillouin scattering and shear rheometry were employed to investigate these new nanoparticle-based fluids. The glass transition temperature and hence the local dynamics are governed by the large counter anions, whereas the flow properties can be controlled by the spatial correlation between the nanoparticles, e.g. by tuning the volume fraction of hard cores and local interactions between segments in the soft corona. Liquid-like ordering of the cores was revealed by X-ray scattering and found to influence significantly the macroscopic flow properties of these salts.

S2 N3+ : An Aromatic SN Cation with an N3 Unit.

Surprisingly stable is the first example of a binary six π electron aromatic SN cation with an N3 unit, S2 N3+ . It can be isolated on a macroscopic scale when a large counter anion is present. The structure determined by X-ray investigations is in good agreement with theoretical data. The unequivocal identification was supported by Raman and infrared studies. The structure and bonding are discussed on the basis of MO (molecular orbital) and AIM (atoms-in-molecules) analysis.

Very Large Counteranion Modulation of Cationic Metallocene Polymerization Activity and Stereoregulation by a Sterically Congested (Perfluoroaryl)fluoroaluminate

We communicate here the unusual structural and cocatalytic features of a new, stable (perfluoroaryl)aluminate anion, tris(2,2`,2``-nonafluorobiphenyl)flouroaluminate (PBA{sup -}). Noteworthy features include very large ion pairing/metallocenium ancillary ligand structural effects on olefin polymerization activity and stereoselectivity. These results considerably expand what is known about the consequences of strong cation-anion interactions for group 4-mediated olefin polymerization. For anions that coordinatively `intrude` into the cation coordination sphere, the effects can be dramatic. 15 refs., 1 tab.