Reversible Redox Waves Research Articles

π-Extended Planarized Triphenylboranes with Thiophene Spacers

Planarized triphenylboranes extended with thiophene or bithiophene spacers were synthesized, which showed intense fluorescences in solution and reversible redox waves for reduction in cyclic voltammetry. Organic light-emitting diodes (OLEDs) using these compounds as an electron-transporting material were fabricated.

Synthesis, experimental and theoretical investigation of a new type nickel dithiolene complex

A new nickel complex with an extended multisulfur dithiolene ligand, [Ni(dmeodddt)2] (dmeodddt=5,6-dimethoxy-5,6-dihydro-1,4-dithiine-2,3-dithiolate), has been synthesized and characterized by IR, Raman, UV–Vis and NMR spectroscopy. Its crystal structure has been determined by X-ray crystallography, showing that the Ni atom is tetra-coordinated and has a square planar geometry with the methoxy groups placed above and below the metal dithiolene core, due to stereochemical hindrance. Electrochemical measurements showed that the complex exhibits four 1e− reversible redox waves. The results of theoretical calculations showed a good agreement with the experimental findings and gave answers about its electronic structure.

Interfacial self-assembly of Zn(Fe)-bisterpyridine coordination polymers, their fluorescent and electrochemical properties in Langmuir–Blodgett films

Metal-bisterpyridine coordination polymers (CPs) have been synthesized at the air–water interface through an interfacial coordination reaction of metal ions (Zn2+/Fe2+) with bidentate ligand of 4,4′′′′-(1,4-phenylene)bis(2,2′:6′2′′-terpyridine) (PBTerpy). Surface pressure-area isotherms indicated that the average molecular area of PBTerpy was about 0.8nm2 on the pure water surface, which slightly increased to about 1nm2 on the inorganic salt subphase surfaces due to the formation of Zn(Fe)-PBTerpy CPs. Monolayers of the Zn(Fe)-PBTerpy CPs were deposited on the quartz, Si and indium tin oxide (ITO) substrate surfaces by the Langmuir–Blodgett (LB) method. The as-prepared LB films were characterized by using UV-vis absorption and fluorescence spectroscopy, X-ray photoelectron spectroscopy, as well as by using scanning electron microscope and atomic force microscope. The pure PBTerpy ligand and its LB films showed a broad fluorescent emission at about 350–370nm. This emission red shifted to about 380–410nm in the LB films of Zn(Fe)-PBTerpy CPs. Time-resolved fluorescent spectra revealed that the emission lifetime was about 1.2–2.4ns for the pure PBTerpy ligand in the dilute methanol solution and its LB films, while it was about 5.0ns in the LB film of Fe-PBTerpy CPs and 20.6ns in the LB film of Zn-PBTerpy CPs. A couple of reversible redox wave was recorded and centered at about −0.53V (vs Ag/AgCl) for the ITO electrode covered by the LB film of Fe-PBTerpy CPs, which was designated to one electron transfer process between the CPs of Fe(II)-PBTerpy and Fe(III)-PBTerpy. Since the PBTerpy can coordinate with lots of transition metal ions, we suggest that the present method may be used to prepare new optically and electrically active organic–inorganic composite materials.

Interfacial assembly and characterization of hybrid ultrathin films of manganese 5,10,15,20-tetra (4-pyridyl) porphine chloride tetrakis (methochloride) and its polymeric derivative with poly (4-vinylpyridine)

Monolayers of a water-soluble metalloporphyrin, manganese tetra-(4-pyridyl) porphine chloride tetrakis (methochloride) (MnTMPyP), and its polymeric derivative with poly (4-vinylpyridine) (MnTMPyP-PVP) have been investigated at the air–water interface. These monolayers were transferred on the substrate surfaces to form hybrid ultrathin films by the Langmuir-Blodgett (LB) method. It was revealed that, although the water-soluble MnTMPyP could not form insoluble monomolecular layer on the pure water surface, it could be stabilized on the NaB(C6H5)4 subphase surface due to an electrostatic interaction between MnTMPyP and B(C6H5)4−, resulting in the formation of MnTMPyP-B(C6H5)4 hybrids. On the other hand, its polymeric derivative of MnTMPyP-PVP could form stable insoluble monolayers on the pure water, NaB(C6H5)4 and Na2PdCl4 subphase surfaces. Composition, structure and microscopic morphology of the as-prepared LB films were characterized by using UV–vis absorption, infrared and X-ray photoelectron spectroscope, as well as scanning electron microscope. The results suggested formation of the hybrid MnTMPyP-B(C6H5)4 and MnTMPyP-(PVP-)B(C6H5)4 and Pd-MnTMPyP-PVP coordination polymer ultrathin films at the interfaces. Cyclic voltammograms of the LB films revealed two couples of reversible redox waves centered at 0.2–0.3 and −0.1 to −0.2V (vs Ag/AgCl), corresponding to the Mn(II)/Mn(III)TMPyP-(PVP-)B(C6H5)4 and Mn(III)/Mn(IV)TMPyP-(PVP-)B(C6H5)4 electron transfer processes of the manganese porphyrins in the LB films.

Electrochemical Sensor for o‐Nitrophenol Based on β‐Cyclodextrin Functionalized Graphene Nanosheets

An electrochemical sensor for the quantification of o‐nitrophenol (o‐NP) has been developed based on the β‐cyclodextrin functionalized graphene nanosheets modified glassy carbon electrode (CD‐GNs/GCE). The results indicated that CD‐GNs showed good electrochemical behavior to the redox of o‐NP which is attributed to the combination of the excellent properties of graphene and cyclodextrin. The peak currents possess a linear relationship with the concentration of o‐NP in the range of 5–400 μM. The detection limit of o‐NP reached to 0.3 μM on the basis of the signal‐to‐noise characteristics (S/N = 3). The peak potentials for the reversible redox waves are not affected by other nitrophenol isomers (m, p‐NP), illustrating good selectivity. Furthermore, the developed electrochemical sensor exhibited good stability and reproducibility for the detection of o‐NP and could be used to determine o‐NP in real water sample.

New Insights into the Electronic Structure and Reactivity of One-Electron Oxidized Copper(II)-(Disalicylidene)diamine Complexes

The neutral and one-electron oxidized Cu(II) six-membered chelate 1,3-Salcn (1,3-Salcn = N,N'-bis(3,5-di-tert-butylsalicylidene)-1,3-cyclohexanediamine) complexes have been investigated and compared with the five-membered chelate 1,2-Salcn (N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-(1R,2R)-diamine) complexes. Cyclic voltammetry of Cu(1,3-Salcn) showed two reversible redox waves at 0.48 and 0.68 V, which are only 0.03 V higher than those of Cu(1,2-Salcn). Reaction of Cu(1,3-Salcn) with 1 equiv of AgSbF6 afforded the oxidized complex which exists as a ligand-based radical species in solution and in the solid state. The X-ray crystal structure of the oxidized complex, [Cu(1,3-Salcn)]SbF6, exhibited an asymmetric metal binding environment with a longer Cu-O bond and quinoid distortion in the phenolate moiety on one side, demonstrating at least partial ligand radical localization in the solid state. The ligand oxidation is also supported by XPS and temperature dependent magnetic susceptibility. The electronic structure of the [Cu(1,3-Salcn)](+) complex was further probed by UV-vis-NIR, resonance Raman, and electron paramagnetic resonance (EPR) measurements, and by theoretical calculations, indicating that the phenoxyl radical electron is relatively localized on one phenolate moiety in the molecule. The reactivity of [Cu(1,3-Salcn)](+) with benzyl alcohol was also studied. Quantitative conversion of benzyl alcohol to benzaldehyde was observed, with a faster reaction rate in comparison with [Cu(1,2-Salcn)](+). The kinetic isotope effect (KIE = k(H)/k(D)) of benzyl alcohol oxidation by [Cu(1,3-Salcn)](+) was estimated to be 13, which is smaller than the value reported for [Cu(1,2-Salcn)](+). The activation energy difference between [Cu(1,2-Salcn)](+) and [Cu(1,3-Salcn)](+) was in good agreement with the energy calculated from KIE. This correlation suggests that the Cu(II)-phenoxyl radical species, characterized for [Cu(1,2-salcn)](+) is more reactive for hydrogen abstraction from benzyl alcohol in comparison to the 1:1 mixture of Cu(III)-phenolate and Cu(II)-phenoxyl radical species, [Cu(1,2-Salcn)](+). Thus, the Cu(II)-phenoxyl radical species accelerates benzyl alcohol oxidation in comparison with the Cu(III)-phenolate ground state complex, in spite of the similar activated intermediate and oxidation pathway.

Copper nano composites functionalized by bis-benzimidazole diamide ligand: Effect of size, co-anion dependent conductivity and band gap studies

Copper (I) and copper (II) nano composites capped with a bis-benzimidazole diamide ligand were prepared by reverse micelle method and characterized using CHNS, FTIR, 1H NMR, TEM and DLS studies. All particles were spherical ranging between 10 and 70 nm. They displayed a quasi reversible redox wave due to the Cu (II)/Cu (I) reduction process. The Eg1′ values shift anodically as NO3− < Cl− < SCN−. Electrochemical HOMO and LUMO band gap (Eg1′) for the nano composites were +1.80 (NO3−), +2.80 (Cl−) and +4.10 (SCN−) eV, respectively. However, the optical band gap (Eg1) for the nano composites was calculated from their absorption edges and lie between 1.77 and 4.13 eV. Fluorescence studies reveal that nano composites in themselves behave as an enhancer and quencher in respect to ligand, Quantum yield (φ) is varying from 0.008 to 0.02 photon. The activation energies range from 34 to 54 kJ mol−1 and are quite low in comparison to that of the free bis-benzimidazole diamide ligand (137 kJ mol−1). The lower activation energies further re-emphasize the nano size of these composites. At room temperature, the dc conductivity lies between 1 × 10−4–9.33 × 10−4 S cm−1 [NO3− > SCN− > Cl−] indicating them to be on the semiconductor insulator interface. The dielectric constant, dielectric loss and the ac conductivity were measured for all nano at room temperature and below the room temperature for the nano composite containing nitrate as co-anion. The conductivity was found to follow the correlated barrier hopping (CBH) mechanism; the exponent factor (s) varies from 0.5 to 1.

Influence of Axial Ligands on Diverse Properties in Three Trinickel String Complexes

Three new trinickel string complexes, [Ni3(dpa)4(3-nba)2](1), [Ni3(dpa)4(4-nba)2]·(CH3OH) (2), and [Ni3(dpa)4(3,5-dnba)2](3) where dpa− is the anion of 2,2′-dipyridylamine, 3-nba− is 3-nitrobenzoate anion, 4-nba− is 4-nitrobenzoate anion, and 3,5-dnba− is 3,5-dinitrobenzoate anion, were synthesized in good yield and characterized by X-ray crystallography, infrared spectra, elemental analysis, magnetic susceptibility, cyclic voltammogram (CV), UV-vis spectra, fluorescence spectra, and TG analysis. The magnetic susceptibilities suggested that the terminal Ni atoms in all three complexes are in high-spin state while the central Ni atom is in a low-spin state. The CVs of complexes 1–3 showed reversible one-electron redox waves at E1/2 = 1.1395 V for 1, 1.108 V for 2, and 1.109 V for 3 corresponding to Ni3 7+/Ni3 6+. The Ni-Ni distances in three complexes are somewhat different, indicating the axial nitrobenzoate ligands have significant effect on the structural assembly. Supplemental materials are available for this article. Go to the publisher's online edition of Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry to view the supplemental file.

Synthesis and Reactivity of 1-[(2-methoxy)benzene]- 3-[benzothiazole]Triazene With Copper(II) or Cobalt(II) Chloride

A new triazene, 1-[(2-methoxy)benzene]-3-[benzothiazole] triazene (HL), has been synthesized and charaterized. In the presence of Et3N, the reaction of HL and CuCl2·2H2O or CoCl2·6H2O gives the triazenide complexes [Cu4L′4(μ-OMe)4] 1 (L′ 1-[benzothiazole]triazene ion) and [Co2L4] 2, respectively. The X-ray crystal structures of both complexes have been obtained. Magnetic studies indicate significant antiferromagnetic coupling between the copper(II) centers or cobalt(II) centers for complexes 1 and 2, with coupling constants (J) of –587 cm−1 for 1 and –147 cm−1 for 2. Complex 2 shows one reversible one-electron redox wave at –0.835 V, and one irreversible oxidation at –0.193 V, which are in accord with the redox potentials of [CoIII-CoII]/[CoII-CoII] and [CoIII-CoIII]/[CoII-CoII] couples, respectively.

Syntheses, structures and electrochemical properties of homoleptic ruthenium(III) and osmium(III) complexes bearing two tris(carbene)borate ligands

Abstract Six-coordinate homoleptic ruthenium(III) and osmium(III) N-heterocyclic carbene complexes [PhB(ImMe)3]2M(OTf) (M = Ru, 1a; M = Os, 1b) with two tris(N-heterocyclic carbene)borate ligands have been prepared and characterized by ESI-MS, elemental analyses, XPS, and single-crystal X-ray diffraction. X-ray diffraction shows that both complexes display octahedral configuration, in which the metal center is coordinated by two tridentate N-heterocyclic carbene ligands. Electrochemical properties of complexes 1a and 1b have been studied by cyclic voltammetry (CV) measurements, which reveal two reversible redox waves at 0.60, − 0.63 V and 0.35, − 0.86 V for 1a and 1b, respectively, indicating the strong donating nature of the tris(N-heterocyclic carbene)borate ligand.

In site formation and growth of Prussian blue nanoparticles anchored to multiwalled carbon nanotubes with poly(4-vinylpyridine) linker by layer-by-layer assembly

Poly(4-vinylpyridine) (P4VB) was grafted to multiwalled carbon nanotubes (MWCNTs) by an in situ polymerization. This grafted polymer plays two roles in the synthesis of Prussian Blue (PB)/MWCNT composites: (1) a stabilizer to protect PB nanoparticles from aggregation; (2) a linker to anchor these nanoparticles on the surface of MWCNTs. The size of PB nanoparticles deposited on MWCNTs can be controlled by in site layer-by-layer coordination of Fe3+ and [Fe(CN)6]4− ions in aqueous solution. The as-prepared PB/P4VP-g-MWCNT composites were characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray powder diffraction, which revealed that these PB nanoparticles were uniformly distributed on the surface of MWCNTs, and grew upon layer-by-layer assembly. A potential use of PB/P4VP-g-MWCNT composites was demonstrated as an electrocatalyst used in the electrochemical detection of l-cysteine. The as-prepared electrodes modified with PB/P4VP-g-MWCNT composites showed two reversible redox waves assigned to a fast surface-controlled processes. The analytical performance for l-cysteine detection is associated with the load of PB nanoparticles onto MWCNTs. In an optimal experiment, for these as-prepared electrodes, their detection limit of l-cysteine can be measured as low as 0.01μM with a sensitivity 778.34nAμM−1cm−2.

Thermotropic ionic liquid crystals by molecular assembly and ion pairing of 4,4′-bipyridinium derivatives and tris(dodecyloxy)benzenesulfonates in a non-polar solvent

The present work reports a simple and versatile pathway to incorporate redox-active 4,4′-bipyridinium (“viologen”) units with two, three, or six charges into dynamically ordered liquid crystalline structures by ionic interactions. A detailed analysis of the structure–property relationship was supported by molecular modelling experiments. Three redox-active 4,4′-bipyridinium (“viologen”) cores, 1,1′-dimethyl (4-pyridin-4-ylpyridinium) di- (MV2+2+2+2+), 1,1′,1′′-[benzene-1,3,5-triyltris(methylene)]tris(4-pyridin-4-ylpyridinium) tri- (V3+3+3+3+3+), and 1,1′,1′′-[benzene-1,3,5-triyltris(methylene)]tris[(methyl) 4-pyridin-4-ylpyridinium] hexa- (MV6+6+6+) cationic halides, were combined with an anionic caesium 3,4,5-tris(dodecyloxy)benzene sulfonate (DOBS) under phase transfer conditions to yield complexes of constant stoichiometry. The formed complexes, MV2+2+2+(DOBS)222, V3+3+3+(DOBS)333 and MV6+6+6+(DOBS)666, were characterized by NMR spectroscopy. Depending on the molecular structure, significantly different characteristics in electrochemical behaviour of ionic liquid crystals (ILCs) with two DOBS anions and a rod-like core (MV2+2+2+2+) were observed compared with ILs with three and six DOBS anions and y-shaped cores (V3+3+3+3+3+), and (MV6+6+6+) cations respectively. We report for the first time a new electroactive thermotropic liquid crystal, MV2+2+2+(DOBS)222, which changes colour from yellow to blue-green above 75 °C typically for redox units in the reduced state. The reduced states of the MV2+2+2+(DOBS)222 complex at E = −2 V exhibit reversible redox waves and have influence on molecular arrangement in the crystal structure as seen by polarisation microscopy. Our ionic liquid crystals have potential applications, due to their low melting temperature, wide temperature range, ionic conductivity, and thermal- and electro-chromism, for instance, for the design of electrochromic displays.

Multistate Redox‐Active Metalated Triarylamines

Abstracttrans‐[(η5‐C5H5)Fe(η5‐C5H4‐η1‐C≡C)Ru(C≡C‐4‐C6H4NPh2)(dppe)2] [4; dppe = 1,2‐bis(diphenylphosphanyl)ethane] and trans,trans,trans‐[{(η5‐C5H5)Fe(η5‐C5H4‐η1‐C≡C)Ru(dppe)2(C≡C‐4‐C6H4)}3N] (7) have been synthesized from trans‐[Ru(C≡C‐4‐C6H4NPh2)Cl(dppe)2] (3) and trans,trans,trans‐[{(dppe)2ClRu(C≡C‐4‐C6H4)}3N] (6), respectively, and the identities of trans‐[Ru(C=CH‐4‐C6H4NPh2)Cl(dppe)2][PF6] (2, precursor to 3), 3, and 4 have been confirmed crystallographically. Chemical oxidation of 4 and 7 afforded the isolable mixed‐valence species 4[PF6] and 7[PF6]3. The CV of 4 reveals sequential loss of three electrons in fully reversible oxidation steps, whereas the CV of 7 shows five reversible redox waves; in contrast, oxidation of the precursor amines HC≡C‐4‐C6H4NPh2 and (HC≡C‐4‐C6H4)3N are irreversible processes. All oxidation processes afford reversible changes in the linear optical properties. Complementary time‐dependent density functional theory (TD‐DFT) studies suggest that the initial oxidation process for 4 and 7 is iron‐centered and is followed by one (for 4) or three (for 7) ruthenium‐centered oxidations. The final reversible oxidation is assigned by TD‐DFT as delocalized along the metalla‐ethynylarylamine moiety. The intense optical changes consequent on reversible oxidation, together with their charge‐transfer character, suggest that 4 and 7 have potential as nonlinear as well as linear optical multistate switches.

Dirhodium Catalysts That Bear Redox Noninnocent Chelating Dicarboxylate Ligands and Their Performance in Intra‐ and Intermolecular C–H Amination

AbstractWe report two new analogues of the well‐known C–H amination catalyst [Rh2(esp)2] (1) (esp = α,α,α′,α′‐tetramethyl‐1,3‐benzenedipropanoate) that bear redox‐active supporting ligands that are structurally similar to esp. The redox‐active ligands are 2‐[3‐(1‐carboxy‐1‐methylethoxy)phenoxy]‐2‐methylpropanoic acid (H2L1) and (3‐methoxycarbonyl‐2,5‐di‐tert‐butylphenoxy)ethanoic acid (H2L2), which react with Rh2(OAc)4 to form the catalysts [Rh2(L1)2] (2) and [Rh2(L2)2] (3). Both 2 and 3 have been characterized by X‐ray crystallography and cyclic voltammetry, inter alia. Compounds 2 and 3 are structurally similar to 1 but show more complex electrochemical features. Whereas 1 has a single reversible redox wave that corresponds to the Rh2II,II/Rh2II,III couple, 2 and 3 show multiple oxidations that are characteristic of ligand‐centered oxidation. Catalysts 1, 2, and 3 perform well in a model intramolecular C–H amination reaction, and all three catalysts perform equally well during the first four hours of a model intermolecular reaction. After this point, 2 and 3 cease to function, whereas 1 continues to be active. These results support the hypothesis that intermolecular C–H amination utilizes two distinct mechanisms: (1) a nitrene interception/insertion mechanism that is fast but ceases to be operative after four hours, and (2) a one‐electron mechanism that is more robust over extended time periods, but requires the catalyst to be able to undergo Rh2‐centered oxidation.

Synthesis, structure, and properties of extended π-conjugated systems bearing sterically crowded triarylphosphines

The sterically crowded triarylphosphines bearing formyl and benzoyl groups were synthesized and characterized by X-ray crystallography. The benzoyl derivative was converted to the p-quinomethane conjugated with the triarylphosphine. The McMurry coupling of the formyl derivative afforded the diarylethene bearing the two sterically-crowded-triarylphosphine moieties. The cyclic voltammograms of these compounds show reversible redox waves corresponding to the oxidation to the radical cations of the triarylphosphines and irreversible or quasi-reversible waves corresponding to the reduction of the acceptor moieties. The electronic and the fluorescence spectra of these π-conjugated systems, especially push-pull substituted derivatives, exhibit bathochromic shift typical of the extended π-conjugated systems especially in the polar solvent, and the large Stokes shift typical of the crowded triarylphosphines is enhanced by conjugation with the acceptor moiety.

Voltammetric Determination of Hemoglobin Using a Pencil Lead Electrode

AbstractIn this paper the electrochemical behavior of hemoglobin (Hb) immobilized on a pencil lead electrode (PLE) was investigated. Immobilization of Hb on the pencil lead electrode was performed by nonelectrochemical and electrochemical methods. In phosphate buffer solution with pH 7.0 Hb showed a pair of well‐defined and nearly reversible redox waves (the anodic and cathodic peak potentials are located at −0.18 V and −0.22 V, respectively). The dependence of the anodic peak potential (Epa) on the pH of the buffer solution indicated that the conversion of HbFe(III)/HbFe(II) is a one‐electron‐transfer reaction process coupled with one‐proton‐transfer. In addition the effect of scan rate on peak currents and peak separation potential was investigated and electrochemical parameters such as α and ks were calculated. In the second part of this work, the ability of the electrode for determination of Hb concentration was investigated. The results showed a linear dynamic range from 0.15 to 2 µM and a detection limit of 0.11 µM. The relative standard deviation is 4.1 % for 4 successive determinations of a 1 µM Hb solution.

Physicochemical properties of solutions and ultrathin films of triple-decker gadolinium tetra-15-crown-5-phthalocyaninate

The ability of the triple-decker gadolinium complex with tetra-15-crown-5-phthalocyanine Gd2(R4Pc)3, (R = 15-crown-5) (1) to form monolayers and Langmuir-Blodgett films (LBFs) was studied for the first time. The charge characteristics of molecules of a triple-decker phthalocyaninate in monolayer, as well as their orientation and adhesion to the water subphase, were controlled by changing the surface pressure, pH, and subphase composition (aqueous solutions containing triethylenetetramine (TETA) and metal cations). It was shown that the presence of Na+ and protonated TETA aminogroups in resulted in an increasing limiting monolayer area and significant decreasing of the monolayer liquid state region. It is proven that the observed effects are caused by the conformational and charge transitions of peripheral crown ethers induced by their interaction with cations. A comparison of the differential reflectance spectra of the complex monolayer on the deionized water surface with UV-Vis absorption spectra of three-layer Gd2(R4Pc)3 LBF and complex solution in chloroform shows that partial complex oxidation and intensive stacking formation occurs already at the stage of monolayer formation on the subphase surface. Electrochemical studies of three-layer LBFs performed at the indium-tin-oxide electrodes (ITO-electrodes) using cyclic voltammetry (CV) showed three reversible redox waves in the potential range −200 to +1100 mV (vs. Ag+/AgCl). All registered peaks remain the same position and intensity upon multiple cycling. plasmon resonance (SPR) measurements allow to register three stable redox states of studied LBF upon applying the external potential. Such behavior shows the possibility to use multistep redox transformations of studied complex LBF for developing of stable and reproducible switchable optoelectronic systems.

Synthesis and properties of a meso-tetraphenylporphyrin and its Zn (II) complex with a dicyanoisophorone borne by double bond in the β pyrrolic position

A novel porphyrin compound (W1) with D-π-A structure and its Zn (II) complex (Zn-W1) have been synthesized. W1 and Zn-W1 show a similar absorption and emission spectra of porphyrins. Their optical properties can be modulated by the substituent in the β pyrrolic position. W1 and Zn-W1 have preferable thermal stability, as indicated from TGA data. And Zn-W1 shows reversible redox wave in its dichloromethane solution. Also, DFT calculations were used to study these two compounds.

Schottky junction/ohmic contact behavior of a nanoporous TiO2thin film photoanode in contact with redox electrolyte solutions

The nature and photoelectrochemical reactivity of nanoporous semiconductor electrodes have attracted a great deal of attention. Nanostructured materials have promising capabilities applicable for the construction of various photonic and electronic devices. In this paper, a mesoporous TiO2 thin film photoanode was soaked in an aqueous methanol solution using an O2-reducing Pt-based cathode in contact with atmospheric air on the back side. It was shown from distinct photocurrents in the cyclic voltammogram (CV) that the nanosurface of the mesoporous n-TiO2 film forms a Schottky junction with water containing a strong electron donor such as methanol. Formation of a Schottky junction (liquid junction) was also proved by Mott–Schottky plots at the mesoporous TiO2 thin film photoanode, and the thickness of the space charge layer was estimated to be very thin, i.e., only 3.1 nm at −0.1 V vs Ag/AgCl. On the other hand, the presence of [Fe(CN)6]4− and the absence of methanol brought about ohmic contact behavior on the TiO2 film and exhibited reversible redox waves in the dark due to the [Fe(CN)6]4−/3− couple. Further studies showed that multiple Schottky junctions/ohmic contact behavior inducing simultaneously both photocurrent and overlapped reversible redox waves was found in the CV of a nanoporous TiO2 photoanode soaked in an aqueous redox electrolyte solution containing methanol and [Fe(CN)6]4−. That is, the TiO2 nanosurface responds to [Fe(CN)6]4− to give ohmic redox waves overlapped simultaneously with photocurrents due to the Schottky junction. Additionally, a second step photocurrent generation was observed in the presence of both MeOH and [Fe(CN)6]4− around the redox potential of the iron complex. It was suggested that the iron complex forms a second Schottky junction for which the flat band potential (Efb) lies near the redox potential of the iron complex.

Comparison of the SOD-like activity of hexacoordinate Mn(II), Fe(II) and Ni(II) complexes having isoindoline-based ligands

Recently, a series of Fe(II) complexes have been published by our group with 3 N-donor 1,3-bis(2′-Ar-imino)isoindoline ligands containing various Ar-groups (pyridyl, 4-methylpyridyl, thiazolyl, benzimidazolyl and N-methylbenzimidazolyl). The superoxide scavenging activity of the compounds showed correlation with the Fe(III)/Fe(II) redox potentials. Analogous, electroneutral chelate complexes with Mn(II) and Ni(II) in 2:1 ligand:metal composition are reported here. Each Mn(II) complex exhibits one reversible redox wave that is assigned as the Mn(III)/Mn(II) redox transition. The E 1/2 spans a 180 mV range from − 98 (Ar = 3-methylpyridyl) to 82 mV (Ar = thiazolyl) vs. the Fc +/Fc depending on the Ar-sidearm. The SOD-like (SOD=superoxide dismutase)activity of all complexes was determined according to the McCord–Fridovich method. The Mn(II) isoindolinates have IC 50 values – determined with 50 μM cytochrome c Fe(III) – that range from (3.22 ± 0.39) × 10 − 6 (Ar = benzimidazolyl) to (10.80 ± 0.54) × 10 − 6 M (Ar = N-methylbenzimidazolyl). In contrast with the Fe(II) complexes, the IC 50 concentrations show no significant dependence on the E 1/2 values in this narrow potential range emphasizing that the redox potential is not the governing factor in the Mn(II)-containing scavengers. The analogous Ni(II) compounds show no redox transitions in the thermodynamically relevant potential range (− 0.40 to 0.65 V vs. SCE) and accordingly, their superoxide scavenging activity (if any) is below the detection level.