Quasi-reversible Process Research Articles

Determination of fast electrode kinetics facilitated by use of an internal reference.

The concept of using an internal reversible reference process as a calibration in the determination of fast electrode kinetics has been developed and applied with the technique of Fourier transformed large amplitude ac voltammetry to minimize the influence of errors arising from uncertainties in parameters such as electrode area (A), concentration (C), diffusion coefficient (D), and uncompensated resistance (Ru). Since kinetic parameters (electron transfer rate constant, k(0), and electron transfer coefficient, α) are irrelevant in the voltammetric characterization of a reversible reaction, parameters such as A, C, D, and Ru can be calibrated using the reversible process prior to quantification of the electrode kinetics associated with the fast quasi-reversible process. If required, new values of parameters derived from the calibration exercise can be used for the final determination of k(0) and α associated with the process of interest through theory-experimental comparison exercises. Reference to the reversible process is of greatest significance in diminishing the potentially large impact of systematic errors on the measurement of electrode kinetics near the reversible limit. Application of this method is demonstrated with respect to the oxidation of tetrathiafulvalene (TTF), where the TTF(0/•+) process is used as a reversible internal reference for the measurement of the quasi-reversible kinetics of the TTF(•+/2+) process. The more generalized concept is demonstrated by use of the Fc(0/+) (Fc = ferrocene) reversible process as an internal reference for measurement of the kinetics of the Cc(+/0) (Cc(+) = cobaltocenium) process. Via the internal reversible reference approach, a k(0) value of 0.55 cm s(-1) was obtained for the TTF(•+/2+) process at a glassy carbon electrode and 2.7 cm s(-1) for the Cc(+/0) one at a carbon fiber microelectrode in acetonitrile (0.1 M Bu4NPF6).

Electrochemistry of Pb(II)/Pb during preparation of lead wires from PbO in choline chloride—urea deep eutectic solvent

The electrochemistry of Pb(II)/Pb on a stainless steel electrode during the preparation of lead wires from PbO in choline chloride (ChCl)-urea deep eutectic solvent (DES) was investigated by means of cyclic voltammetry, cathodic polarization and chronoamperometry. The experimental results indicated that the reduction of Pb(II) to Pb is a quasi—reversible process controlled by diffusion at temperature varying from 323 to 343 K, and the corresponding apparent activation energy Ea is 52.37 kJ mol-1. The analysis of chronoamperometry measurements suggested that the initial stage of nucleation of lead on stainless steel electrode is a three-dimensional instantaneous nucleation under diffusion control. The effects of reaction time and temperature on the morphology of lead deposits are also examined. The lead wires obtained at 343 K for 120 min have a mean particle size of 30 µ.m in length and 2.5 µ.m in diameter. Based on experimental evidence, the deposition mechanism of sub-micrometer lead wires on stainless steel substrate is proposed by diffusion controlled growth mechanism.

Electrodeposition behavior of bright nickel in air and water-stable betaine·HCl–ethylene glycol ionic liquid

The electrodeposition behaviors of nickel on glassy carbon (GC) and carbon steel (CS) electrodes were investigated in the 14.3%–85.7% (mole fraction) betaine·HCl–ethylene glycol (EG) ionic liquid using cyclic voltammetry and chronoamperometry. The results indicated that the reduction of Ni(II) on CS electrode via a diffusion-controlled quasi-reversible process was much more facile and easier than that occurred on GC electrode, which followed a diffusion-controlled three-dimensional instantaneous nucleation and growth. Scanning electron microscopy was used to observe that the deposit was dense and contained fine crystallites with average size of (80±4) nm. Energy dispersive spectrometer analysis showed that the obtained deposit was metallic nickel. X-ray diffraction spectroscopy indicated that (111) plane was the most preferred crystal orientation. The nickel deposit was luminous and bright, and had good adhesion with the CS substrate.

New Hybrid Nanomaterial Based on Self-Assembly of Cyclodextrins and Cobalt Prussian Blue Analogue Nanocubes.

Supramolecular self-assembly has been demonstrated to be a useful approach to developing new functional nanomaterials. In this work, we used a cobalt Prussian blue analogue (PBA, Co3[Co(CN)6]2) compound and a β-cyclodextrin (CD) macrocycle to develop a novel host-guest PBA-CD nanomaterial. The preparation of the functional magnetic material involved the self-assembly of CD molecules onto a PBA surface by a co-precipitation method. According to transmission electronic microscopy results, PBA-CD exhibited a polydisperse structure composed of 3D nanocubes with a mean edge length of 85 nm, which became shorter after CD incorporation. The supramolecular arrangement and structural, crystalline and thermal properties of the hybrid material were studied in detail by vibrational and electronic spectroscopies and X-ray diffraction. The cyclic voltammogram of the hybrid material in a 0.1 mol·L−1 NaCl supporting electrolyte exhibited a quasi-reversible redox process, attributed to Co2+/Co3+ conversion, with an E1/2 value of 0.46 V (vs. SCE), with higher reversibility observed for the system in the presence of CD. The standard rate constants for PBA and PBA-CD were determined to be 0.07 and 0.13 s−1, respectively, which suggests that the interaction between the nanocubes and CD at the supramolecular level improves electron transfer. We expect that the properties observed for the hybrid material make it a potential candidate for (bio)sensing designs with a desirable capability for drug delivery.

Characterization of a Novel Dioxomolybdenum Complex by Cyclic Voltammetry

Metalloenzymes that carry a pterin-based molybdenum cofactor in their center catalyze numerous reactions in the human body and play a crucial role in its metabolism. Specifically, these enzymes promote redox reactions and oxygen transport in the body. Their absence may cause many problems leading to disability or even death in early childhood. Therefore, model compounds need to be synthesized and analyzed to investigate the reactivity, redox potential, and geometry of these cofactors. This study focused on electrode processes and determined the redox potentials of the new bis-(4-mercapto-5-(p-tolyl)-3H-1,2-dithiole-3-thione)-dioxomolybdenum complex by cyclic voltammetry. The 4-mercapto-5-(p-tolyl)-3H-1,2-dithiole-3-thione ligand underwent irreversible oxidation and reduction at thiol and thione functional groups. The new dioxomolybdenum complex showed a quasi-reversible two-stage electrode process.

Study the voltammetric behavior of 10-Hydroxycamptothecin and its sensitive determination at electrochemically reduced graphene oxide modified glassy carbon electrode

The electrochemical properties of 10-Hydroxycamptothecin were investigated systematically at a reduced graphene oxide modified glassy carbon electrode. A new pair of redox peaks of 10-Hydroxycamptothecin was reported for the first time with quasi-reversible process driven by adsorption. The dynamics parameters of electrode process were calculated using various electrochemical techniques. Owing to the large surface area, good conductivity of electrochemically reduced graphene oxide, the sensor exhibited sensitive activity for 10-Hydroxycamptothecin, displaying a wide linear response from 1.5×10−8molL−1 to 5.0×10−7molL−1 and 5.0×10−7molL−1 to 3.0×10−6molL−1 (Fig. 8). A simple, sensitive and new voltammetric method for the determination of 10-Hydroxycamptothecin was proposed with a determination limit of 1.5×10−8molL−1 and recoveries were determined in the range of 94.2–104%.

Influence of Electron-Withdrawing Substituents on the Electronic Structure of Oxidized Ni and Cu Salen Complexes.

Nickel (Ni(Sal(CF3))) and copper (Cu(Sal(CF3))) complexes of an electron-poor salen ligand were prepared, and their one-electron oxidized counterparts were studied using an array of spectroscopic and theoretical methods. The electrochemistry of both complexes exhibited quasi-reversible redox processes at higher potentials in comparison to the M(Sal(R)) (R = (t)Bu, OMe, NMe2) analogues, in line with the electron-withdrawing nature of the para-CF3 substituent. Chemical oxidation, monitored by ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy, afforded their corresponding one-electron oxidized products. Ligand-based oxidation was observed for [Ni(Sal(CF3))](+•), as evidenced by sharp NIR transitions in the UV-vis-NIR spectrum and a broad isotropic signal at g = 2.067 by solution electron paramagnetic resonance (EPR) spectroscopy. Such sharp NIR transitions observed for [Ni(Sal(CF3))](+•) are indicative of a delocalized electronic structure, which is in good agreement with electrochemical measurements and density functional theory (DFT) calculations. In addition, the increased Lewis acidity of [Ni(Sal(CF3))](+•), evident from the EPR g-value and DFT calculations, was further quantified by the binding affinity of axial ligands to [Ni(Sal(CF3))](+•). For [Cu(Sal(CF3))](+), an intense ligand-to-metal charge transfer band at 18 700 cm(-1) in the UV-vis-NIR spectrum was observed, which is diagnostic for the formation of a Cu(III) species [J. Am. Chem. Soc., 2008, 130, 15448-15459]. The Cu(III) character for [Cu(Sal(CF3))](+) is further confirmed by (19)F NMR analysis. Taken together, these results show that the electron-deficient salen ligand H2Sal(CF3) increases the Lewis acidity of the coordinating metal center.

Spin Crossover, Reversible Redox, and Supramolecular Interactions in 3d Complexes of 4-(4-Pyridyl)-2,5-dipyrazyl-pyridine.

A new terpyridine-inspired terdentate ligand, 4-(4-pyridyl)-2,5-dipyrazyl-pyridine (py-pzpypz), featuring three "spare" nitrogen donors "out the back", has been used to synthesize five bis-ligand complexes, [M(II)(py-pzpypz)2]X2, where M = Mn with X = ClO4, or M = Fe, Co, Ni, and Zn with X = BF4. In contrast, when M = Cu(II), regardless of the M:L ratio employed, 1:1 M:L products were obtained: for X = BF4 a 1D chain {[Cu(II)(py-pzpypz)(DMF)2](BF4)2}n, and for X = Cl a monometallic complex [Cu(py-pzpypz)Cl2]. All seven complexes were structurally characterized, confirming the expected N6 coordination of the M(II) centers in all cases except Cu(II). Notably, a Jahn-Teller elongation is observed in the Co(II) complex, consistent with it being low spin at 100 K. The Cu(II) 1D chain complex has an N4O2 coordination sphere as in this case the "spare" pyridine donor out the back of the py-pzpypz ligand bridges to the next Cu(II) center in the chain, hence providing both a terdentate site and a monodentate pyridine to the next Cu(II) center, and the coordination sphere is completed by weak axial coordination by two DMF solvent molecules. The Cu(II) center in the monometallic complex has an N3Cl2 square pyramidal coordination sphere. In all cases, the noncoordinating, "spare", pyrazine nitrogen atoms are involved in interesting intermolecular interactions, including NPz-π interactions and nonclassical C-H···NPz hydrogen bonding. The Fe(II) complex is low spin as expected. Two polymorphs of the Co(II) complex were obtained, both of which showed gradual spin crossover, with a room temperature T1/2. Two reversible redox processes are observed for [Co(II)(py-pzpypz)2](BF4)2, with Em(M(I)/M(II)) = -0.63 V and Em(M(II)/M(III)) = +0.37 V, and a quasireversible redox process for [Fe(II)(py-pzpypz)2](BF4)2, with Em(M(II)/M(III)) = +1.26 V, versus 0.01 M AgNO3/Ag in MeCN. These potentials are shifted to significantly higher potentials (by ∼0.45 V) than the literature values for the corresponding Fe(II) and Co(II) complexes of the equivalent all-pyridine ligand, consistent with replacement of the two pyridine rings by two pyrazine rings significantly stabilizing the lower oxidation states.

New core-substituted with electron-donating group 1,8-naphthalimides towards optoelectronic applications

New 1,8-naphthalimides with thiophene or bithiophene structure attached by an imine linkage to naphthalene core were synthesized. The structures of obtained compounds were characterized by FTIR, 1H NMR spectroscopy, elemental analysis and for elected compounds by HRMS (ESI) spectrometry. Thermal, optical and electrochemical properties of obtained 1,8-naphthalimides were investigated. Most of them exhibited glass-forming properties with glass transition temperatures in the range of 73–278°C. Optical properties of the prepared compounds were examined by UV–vis and photoluminescence (PL) measurements. They emitted light in chloroform solution with emission maximum at ca. 500nm with the highest quantum yield of fluorescence around 0.46 and green one in NMP solution. In blend with PMMA blue emission was observed with the highest quantum yield of fluorescence around 0.24. All compounds are electrochemically active, and undergo reversible reduction and irreversible or quasi-reversible oxidation process as was found in cyclic and differential pulse voltammetry (CV and DPV) studies. They showed electrochemical band gaps in the range 2.28–2.68eV. Additionally, the electronic properties, that is, orbital energies and resulting energy gap were calculated by density functional theory (DFT). Additionally, selected compounds were preliminary tested as electroluminescence materials in devices with structure ITO/PVK:NI blend/Al.

TTFs nonsymmetrically fused with alkylthiophenic moieties.

Two new dithiolene ligand precursors, containing fused TTF and alkyl thiophenic moieties 3,3'-{[2-(5-(tert-butyl)thieno[2,3-d][1,3]dithiol-2-ylidene)-1,3-dithiole-4,5-diyl]bis[sulfanediyl]}dipropanenitrile (α-tbtdt, 1), and 3,3'-{[2-(5-methylthieno[2,3-d][1,3]dithiol-2-ylidene)-1,3-dithiole-4,5-diyl]bis[sulfanediyl]}dipropanenitrile (α-mtdt, 2), were synthesized and characterized. The electrochemical properties of these electronic donors were studied by cyclic voltammetry (CV) in dichloromethane. Both compounds show two quasi-reversible oxidation processes, versus Ag/AgCl, typical of TTF donors at E11/2 = 279 V and E21/2 = 680 V for 1 and E11/2 = 304 V and E21/2 = 716 V in the case of 2. The single-crystal X-ray structure of 1 and of a charge transfer salt of 2, (α-mtdt)[Au(mnt)2] (3), are reported.

Ionic Liquid Electrolytes for Redox Flow Batteries

The development of efficient devices that store energy generated from intermittent resources (such as solar energy or wind energy) will play a crucial role for sustainable energy supply. Redox flow batteries (RFBs) are considered to be one of the most promising energy storage devices owing to their capacity for storing very large amounts of energy, low cost and high flexibility of design.1 RFBs store electrical energy by chemical changes to species dissolved in aqueous acidic media in two reaction compartments, which are separated by an ion-conducting membrane.1 However, the use of aqueous systems significantly limits the energy and power density of the RFBs due to the narrow potential window of water. A number of non-aqueous electrolytes based on ruthenium, vanadium, manganese and chromium have been reported in order to increase the cell voltage.2 Notably, a cell potential of 2.2 V was reported in a system that employed vanadium and acetonitrile electrolytes.3 The main problem of non-aqueous RFBs is the possibility that the organic solvents in the liquid electrolytes can evaporate during operation and result in poor long-term stability. Moreover, organic solvents are highly flammable, which may pose a serious hazard. In an effort to combat this problem, we propose room temperature ionic liquids (RTILs) as electrolytes in RFBs. RTILs are thermally stable, non-flammable, conductive and, crucially exhibit very wide electrochemical windows of up to 6.0 V.4 In this poster, the electrochemical behavior of several RFB redox mediators are examined at glassy carbon (GC) electrodes using a RTIL as the electrolyte. The RTIL was 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C2C1Im][Tf2N], see inset of Figure 1C), and this RTIL was chosen because it has a low viscosity and a large electrochemical window. Figure 1A shows the CVs recorded at GC in 10 mM V(acac)3 in ([C2C1Im][Tf2N], and this response is similar to the electrochemical behavior of V(acac)3 in acetonitrile.3 Three oxidation and reduction processes were observed which were attributed to the redox process of V3+/V2+ (A1/C1), V3+/V4+ (A2/C2) and V4+/V5+(A3/C3). Each process displayed an electrochemically quasi-reversible response. The potential difference between A1/C1 and A2/C2 is 2.0 V and can reach upto 2.3 V for (A1/C1)/A3/C3). Two redox processes were observed when Mn(acac)3 in ([C2C1Im][Tf2N] was studied (Figure 1B). The oxidation/reduction of Mn3+ to Mn2+ (A1/C1) is electrochemically irreversible and its peak-to-peak separation is about 0.55 V at 50 mV s-1, while the Mn3+/Mn4+(A2/C2) is quasi-reversible process with peak-to-peak separation of 0.1 V at 50 mV s-1. In the case of Cr electrochemistry in [C2C1Im][Tf2N], electrochemical analysis indicated that the electro generated Cr4+ (A3/C3) is unstable in this RTIL, suggesting the presence of an additional chemical step during electron transfer (see Figure 1C, A2/A2 was assigned to the redox process of Cr3+/Cr2+ and A1/C1 was to Cr2+/Cr1+). Notably, a similar electrochemical response was also observed when acetonitrile was used as the electrolyte.5 The diffusion coefficients of V, Cr and Mn in [C2C1Im][Tf2N] are 1.8 x 10-7 cm2 s-1, 1.6 x 10-7 cm2 s-1 and 1.5 x 10-7 cm2 s-1 respectively. Finally, the effect of ionic liquid composition (changing the anions) on the electrochemistry of each redox mediator will be presented.

CTAB functionalized graphene oxide/multiwalled carbon nanotube composite modified electrode for the simultaneous determination of sunset yellow and tartrazine

We have developed hexadecyl trimethyl ammonium bromide (CTAB) functionalized graphene oxide (GO)/multiwalled carbon nanotubes (MWNTs) modified glassy carbon electrode (CTAB-GO/MWNT/GCE) as a novel system for the simultaneous determination of two synthetic food colorants, sunset yellow (SY) and tartrazine (TZ). Cyclic voltammetric (CV) studies indicate that SY and TZ undergo reversible and quasi-reversible redox processes on CTAB-GO/MWNT/GCE, respectively, with substantially lowered peak potentials, suggesting the extraordinary electrocatalytic effect of CTAB-GO/MWNT/GCE. Further study revealed that the electrode reactions of both SY and TZ are predominantly adsorption-controlled process on the CTAB-GO/MWNT/GCE. At the same time, the oxidation peak potentials of SY and TZ were effectively separated on CTAB-GO/MWNT/GCE, and their simultaneous determination was possible. Operational parameters, such as the accumulation time, solution pH, and scan rate, which affect the analytical performance of determination, were optimized. The CTAB-GO/MWNT/GCE behaved linearly to SY and TZ in the concentration range of 1 × 10−7 to 2 × 10−5 M and 3 × 10−8 to 6 × 10−7 M with a detection limit of 1 × 10−8 M and 5 × 10−9 M, respectively. The proposed method was successfully utilized for simultaneous determination of SY and TZ in real food samples.

Synthesis, structural, electrochemical, and spectroscopic studies of some (diimine)ruthenium nitrile complexes

The syntheses of cationic ruthenium(II) complexes [Ru(Me2-bpy)(PPh3)2RRʹ][PF6]x {Me2-bpy = 4,4ʹ-dimethyl-2,2ʹ-bipyridine, (3) R = Cl, Rʹ = N≡CMe, x = 1, (4) R = Cl, Rʹ = N≡CPh, x = 1, (5) R = Rʹ = N≡CMe, x = 2} and [Ru(Me2-bpy)(κ2-dppf)RRʹ][PF6]x {dppf = 1,1ʹ-bis(diphenylphosphino)ferrocene, (6) R = Cl, Rʹ = N≡CMe, x = 1, (7) R = Cl, Rʹ = N≡CPh, x = 1, (8) R = Rʹ = N≡CMe, x = 2} are reported, together with their structural confirmation by NMR (31P, 1H) and IR spectroscopy and elemental analysis, and, in the case of trans-[Ru(Me2-bpy)(PPh3)2(N≡CCH3)Cl][PF6] (3), by X-ray crystallography. Electronic absorption and emission spectra of the complexes reveal that all complexes except 4 and 6 are emissive in the range 370–400 nm with 8 exhibiting an emission in the blue. Cyclic voltammetry studies of 3–8 show reversible or quasi-reversible redox processes at ca. 1 V, assigned to the Ru(II/III) couple.

Iron(III) and copper(II) complexes of trans-bis(ferrocenyl)porphyrin: Effect of metal ions on long-range electronic communication

A series of complex with a general formula of M(Fc2Ph2P) [Fc2Ph2P = 5,10-bisferrocenyl-15,20-bisphenylporphyrin (2 −); M = Fe(III)Cl Fe(III)(ClO4) and Cu(II)] have been synthesized and characterized. The single crystal X-ray structure of Cu II(Fc2Ph2P) has been reported in which two ferrocene moieties are in anti form with respect to each other. The ferrocenyl groups of Cu II(Fc2Ph2P) are more easily oxidized via a single two-electron quasi-reversible process compared to the free base ligand in which two 1e-oxidative response separated by 0.23 V are observed. Electrochemical study of FeIII(Fc2Ph2P)Cl revealed ferrocene-based two-electron quasi-reversible oxidation at 0.72 V indicating no observable coupling of the ferrocene moieties. The higher oxidation state of Fe(III) reduces the electron releasing tendency of the porphyrin ring and thus make the ferrocene oxidation difficult. The porphyrin, however, lack substituents at the β-pyrrolic positions, and the ferrocenyl moieties are therefore free to rotate. The observed electrochemical analyses thus demonstrate that the oxidation of the ferrocene subunit is strongly affected by porphyrin ring as well as the central metal through extended π-conjugation.

Kinetics of reduction of nitric acid by electrochemical method and validation of cell design for plant application

Employing electrochemical method, the concentration of nitric acid had been reduced from 4 to about 0.5M, under constant current/potential conditions in batch mode, for the purpose of optimizing the process parameters for the destruction of nitric acid in radioactive liquid waste, with good energy efficiency. Based on the rate constants determined from the batch process, a cell assembly in cylindrical configuration was designed for the electro-reduction of nitric acid in continuous mode, in radioactive environment. The steady state concentration of the acid at the outlet was compared with that concentration calculated using model equation and the agreement between the two sets of data was found to be reasonable. Cyclic voltammetric runs were recorded to understand the reduction behavior of nitric acid on platinum electrode. The results revealed the reduction of nitrate ion to be a quasi–reversible process and for the scan rate of 0.1Vs−1, values of 3.3×10−6cm2s−1 and 1.37×10−3cms−1 were computed for the diffusion coefficient and heterogeneous electron transfer rate constant, respectively.

Electrochemical behaviour of Cu(II)/Cu(I) redox couple in 1-hexyl-3-methylimidazolium chloride ionic liquid

The electrochemical behaviour of Cu(II)/Cu(I) redox couple in 1-hexyl-3-methylimidazolium chloride (C6mimCl) ionic liquid was studied using glassy carbon electrode at 375 K by cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy. In this electrochemical study, we have made an attempt to avoid the problem of water contamination in hygroscopic C6mimCl ionic liquid by setting the temperature at 375 K without glove box. This high temperature cyclic voltammetric study revealed two-step one electron reductions of Cu(II) to Cu(I) followed by Cu(I) to Cu metal. The reduction of Cu(II) to Cu(I) was found to be quasi-reversible at 375 K. The diffusion coefficients of Cu(II) and Cu(I), and the charge transfer rate constant of Cu(II) in C6mimCl were estimated by Randles-Ševčik equation and Nicholson’s method, respectively, and found to be consistent with the quasi-reversible process. Further, constant potential electrodeposition of metallic copper was carried out on a stainless steel electrode at 375 K and the deposit was characterised by X-ray diffraction and electron microscopy. Quasi-reversible behavior of Cu(II)/Cu(I) redox couple in C6mimCl is studied at 375 K. Diffusion and mass transport coefficients as well as charge transfer rate constant of copper species are estimated. Copper on stainless-steel electrodes by constant potential electrolysis shows island growth of Cu particles under the influence of C6mimCl.

The Study of Redox Electrode Processes of Sulfur-Containing Compounds by Voltammetry

In this work the general case of quasi-reversible redox electrode processes of thiol compounds proceeding on a mercury-film electrode via a CE (chemical-electrochemical) mechanism has been revealed and investigated by voltammetry. The quantitative criteria for correlation between theory and experiment corresponding to a CE mechanism and new approach for estimating the kinetic parameters of the preceding chemical reaction have been suggested.

Synthesis, characterization, single crystal X-ray determination, fluorescence and electrochemical studies of new dinuclear nickel(II) and oxovanadium(IV) complexes containing double Schiff base ligands

A series of new bimetallic complexes of nickel(II) and vanadium(IV) have been synthesized by the reaction of the new double bidentate Schiff base ligands with nickel acetate and vanadyl acetylacetonate in 1:1M ratio. In nickel and also vanadyl complexes the ligands were coordinated to the metals via the imine N and enolic O atoms. The complexes have been found to possess 1:1 metals to ligands stoichiometry and the molar conductance data revealed that the metal complexes were non-electrolytes. The nickel and vanadyl complexes exhibited distorted square planar and square pyramidal coordination geometries, respectively. The emission spectra of the ligands and their complexes were studied in methanol. Electrochemical properties of the ligands and their metal complexes were also investigated in DMSO solvent at 150mVs−1 scan rate. The ligands and metal complexes showed both quasi-reversible and irreversible processes at this scan rate. The Schiff bases and their complexes have been characterized by FT-IR, 1H NMR, UV/Vis spectroscopies, elemental analysis and conductometry. The crystal structure of the nickel complex has been determined by single crystal X-ray diffraction.

Ruthenium(II) and osmium(II) mixed chelates based on pyrenyl-pyridylimidazole and 2,2'-bipyridine ligands as efficient DNA intercalators and anion sensors.

We report herein the synthesis and characterization of two monometallic ruthenium(II) and osmium(II) complexes of composition [(bpy)2M(HImzPPy)] (ClO4)2 derived from pyrenylimidazole-10-pyridin-2-yl-9H-9,11-diazacyclopenta[e]pyrene (HImzPPy) and 2,2'-bipyridine (bpy) ligands. X-ray crystallographic study shows that both crystals belong to the triclinic system having space group P1̅. The photophysical properties of 1 and 2 in acetonitrile indicate that the metal-to-ligand charge-transfer excited state is mainly centered in the [M(bpy)2](2+) moiety of the complexes and slightly affected by the extended conjugation of the pyrenylimidazole moiety. Both complexes display one-electron reversible metal-centered oxidative processes and a number of quasi-reversible reductive processes. The binding affinities of the complexes toward calf-thymus DNA (CT-DNA) were thoroughly studied through different methods such as absorption, emission, excited-state lifetime, circular dichroism, and thermal denaturation of DNA and a relative DNA binding study using ethidium bromide. All of these experiments account for the intercalative nature of both 1 and 2 toward CT-DNA as well as their light-switch behavior. The anion recognition study through different spectroscopic techniques reveals that both complexes act as "turn-on" luminescence sensors for H2PO4(-) and "turn-off" sensors toward F(-) and AcO(-). The imidazole N-H proton of the receptors gets deprotonated with the excessive addition of F(-) and AcO(-), while it interacts with H2PO4(-) through hydrogen-bonding interaction. Theoretical calculations (DFT and TD-DFT) were also performed to understand the photophysical properties of the metalloreceptors.

Electrochemical behavior of cerium(III) in NaCl–KCl molten salt

The electro-redox behavior of uranium(III) on Mo electrode in NaCl–KCl molten salt in the temperature range 973–1073 K has been investigated using cyclic voltammetry electrochemical method and so on, such research will help to understand uranium behavior in pyro-reprocessing. The results showed that UCl3 could be reduced into uranium metal in a quasi-reversible one-step process exchanging three electrons. The diffusion coefficients of U(III) ions were determined and the activation energy for diffusion was found to be 55.794 kJ mol−1. The apparent standard potentials of U(III)/U(0) at several temperatures were calculated. The thermodynamic properties of UCl3 have also been investigated.