Quasi-reversible Redox Process Research Articles

Synthesis of Ni3V2O8-rGO composite nanostructure for high-performance hybrid supercapacitors via hydrothermal method

To address global energy demand, major efforts have been made to develop cutting-edge electrode materials for electrochemical energy storage (EES) devices. The present article discusses the hydrothermal synthesis of bare nickel vanadate and a nickel vanadate/reduced graphene oxide (Ni3V2O8-rGO) composite for supercapacitor applications. The physicochemical properties of pure Ni3V2O8 (NVO) and the Ni3V2O8-rGO (NVO-rGO) composite were investigated using a variety of characterization tools. The electrochemical traits of the NVO-rGO composite outperform bare NVO due to the synergistic effect. At a current density of 1 mAcm−2, the NVO and NVO-rGO nanostructures exhibit excellent specific capacitances of 85 Fg−1 and 108 Fg−1, respectively. These nanostructures also have energy densities of about 3.82 and 5.02 WhKg−1, with power densities of 141.75 and 151.57 WKg−1 for NVO and NVO-rGO composite, respectively. Electrochemical impedance spectroscopy (EIS) studies revealed a charge resistance of 2.05 Ω. The transfer coefficient and standard rate constant indicate that the charge storage mechanism is based on a quasi-reversible redox process. The present investigation demonstrates that the NVO-rGO composite has exceptional electrochemical performance. The outstanding electrochemical performance of both NVO and NVO-rGO underlines their potential as novel and promising materials for supercapacitor applications, implying significant feasibility for large-scale utilization.

New copper carboxyl-ate pyrene dimers: synthesis, crystal structure, Hirshfeld surface analysis and electrochemical characterization.

Two new copper dimers, namely, bis-(dimethyl sulfoxide)-tetra-kis-(μ-pyrene-1-carboxyl-ato)dicopper(Cu-Cu), [Cu2(C17H9O2)4(C2H6OS)2] or [Cu2(pyr-COO-)4(DMSO)2] (1), and bis-(di-methyl-formamide)-tetra-kis-(μ-pyrene-1-carboxyl-ato)dicopper(Cu-Cu), [Cu2(C17H9O2)4(C3H7NO)2] or [Cu2(pyr-COO-)4(DMF)2] (2) (pyr = pyrene), were synthesized from the reaction of pyrene-1-carb-oxy-lic acid, copper(II) nitrate and tri-ethyl-amine from solvents DMSO and DMF, respectively. While 1 crystallized in the space group P , the crystal structure of 2 is in space group P21/n. The Cu atoms have octa-hedral geometries, with four oxygen atoms from carboxyl-ate pyrene ligands occupying the equatorial positions, a solvent mol-ecule coordinating at one of the axial positions, and a Cu⋯Cu contact in the opposite position. The packing in the crystal structures exhibits π-π stacking inter-actions and short contacts through the solvent mol-ecules. The Hirshfeld surfaces and two-dimensional fingerprint plots were generated for both compounds to better understand the inter-molecular inter-actions and the contribution of heteroatoms from the solvent ligands to the crystal packing. In addition, a Cu2+/Cu1+ quasi-reversible redox process was identified for compound 2 using cyclic voltammetry that accounts for a diffusion-controlled electron-donation process to the Cu dimer.

Four Redox Isomers of a [3 × 3] Copper-Iron Heterometal Grid.

A mixed-valence heterometallic nonanuclear [3 × 3] grid complex, [CuI2CuII6FeIII(L)6](BF4)5·MeOH·9H2O (1; MeOH = methanol), was synthesized by a one-pot reaction of copper and iron ions with multidentate ligand 2,6-bis[5-(2-pyridinyl)-1H-pyrazol-3-yl]pyridine (H2L). 1 showed five quasi-reversible one-electron redox processes centered at +0.74, +0.60, +0.39, +0.27, and -0.13 V versus SCE, assignable to four CuI/CuII processes and one FeII/FeIII couple, respectively. The two-electron-oxidized species [CuII8FeIII(L)6](PF6)7·4MeOH·7H2O (12eOx), the two-electron-reduced species [CuI4CuII4FeIII(L)6](PF6)3·2H2O (12eRed), and the three-electron-reduced species [CuI4CuII4FeII(L)6](PF6)2·5MeOH·H2O (13eRed) were isolated electrochemically. The four redox isomers were characterized by single-crystal X-ray analysis, SQUID magnetometry, and Mössbauer spectroscopy.

Sulfonamido-Pincer Complexes of Cu(II) and the Electrocatalysis of O2 Reduction.

Heteroleptic copper complexes of an asymmetrical pincer ligand containing a central anionic sulfonamide donor (pyridine-2-yl-sulfonyl)(quinolin-8-yl)-amide (psq), which contains a central anionic sulfonamido donor have been prepared. Meridional κ3-N,N″,N‴ binding with the co-ligands acetate, chloride, or acetonitrile (MeCN), trans to the central sulfonamido N-donor, is revealed by the X-ray crystal structures of [Cu(OAc)(psq)(H2O)], [CuCl(psq)]2, and [Cu(psq)(MeCN)](PF6). Either overall distorted square pyramidal or octahedral geometries of the copper atom are satisfied by coordinated water in the case of the acetate complex or interactions with periphery sulfonamido oxygen atoms on adjacent molecules in the dimeric chloride and 1D polymeric acetonitrile complexes. The cyclic voltammogram (CV) of [Cu(OAc)(psq)(H2O)] shows a quasi-reversible CuII/CuI reduction at -0.930 V (vs Fc+/Fc0, MeCN), and an irreversible CuII/CuI reduction for [Cu(psq)(MeCN)](PF6) is seen at -0.838 V. This signal is split into two quasi-reversible redox processes on the addition of 2,2,2-trifluoroethanol (TFE). This suggests that TFE pushes a solution equilibrium toward a dimeric acetate complex analogous to [CuCl(psq)]2, which shows two quasi-reversible waves at -0.666 V and -0.904 V vs Fc+/Fc0 consistent with its dimeric solid-state structure. A comparison of the CVs of [Cu(OAc)(psq)(H2O)] under either a N2 or an O2 atmosphere revealed that this complex catalyzes turnover electro-reduction of O2 to H2O2 and H2O. The rate of reaction increases on addition of a weak organic acid, and a coulombic efficiency of 48% for H2O2 was determined by iodometric titration. We propose that a CuI complex formed on electroreduction binds O2 to yield an intermediate superoxide complex. On electron and proton transfer to this species, a bifurcated route back to the O2-activating CuI complex is feasible with either release of H2O2 or O-O cleavage resulting in the liberation of H2O. The CuI complex is regenerated by subsequent reduction and protonation to close the cycle.

Effects of nickel–cobalt material properties on glucose catalysis

The development of non-enzymatic glucose sensors becomes even more significant as the number of diabetics worldwide continues to increase. Ni–Co alloy can be fabricated by electrodeposition and used as a catalyst for glucose so that it is a suitable electrode material for non-enzymatic electrochemical glucose sensors. The results of material analyses reveal that the catalytic performance for glucose is related to the crystallographic structure of Ni–Co alloy. A Ni–Co based non-enzymatic glucose sensor with a majority of hexagonal close packed (hcp) lattice exhibits better catalytic performance and, moreover, the catalysis of glucose is a quasi-reversible redox process, either in film-type or nanowire-type alloy. However, the nanowire-type Ni–Co glucose sensor has a wider sensing range than the film-type sensor. Ni–Co glucose sensor possesses excellent anti-interference without being influenced by the chemicals coexisting with glucose. These results demonstrate the effect of the crystal structure of Ni–Co on glucose catalysis and suggest the electroplating conditions for the preparation of Ni–Co non-enzymatic glucose sensor with good catalytic performance and excellent anti-interference ability.

Pentamethylcyclopentadienyl Complexes of Cerium(IV): Synthesis, Reactivity, and Electrochemistry.

Treatment of Cp*2CeCl2K(THF) with alkali-metal alkoxides and siloxides in the presence of hexachloroethane generates the monomeric bis(pentamethylcyclopentadienyl) cerium(IV) complexes Cp*2Ce(OR)2 (Cp* = C5Me5; R = Et, iPr, CH2tBu, tBu, SiMe3, or SiPh3). Large substituents R trigger ligand scrambling to half-sandwich complexes Cp*Ce(OR)3, which could be isolated for R = tBu and SiPh3. Similar reactions with sodium aryloxide NaOAr (OAr = OC6H3iPr2-2,6) led to Cp*2Ce(OAr)Cl. Treatment of tris(cyclopentadienyl) complexes CpR3CeCl (CpH = Cp = C5H5; CpMe = C5H4Me) with NaOAr afforded CpMe2Ce(OAr)2 and Cp3Ce(OAr). The cerium(IV) complexes display a pseudotetrahedral geometry in the solid state. Cyclic voltammetry revealed mostly chemically reversible as well as electrochemically quasi-reversible redox processes with potentials ranging from -0.84 to -1.61 V versus Fc/Fc+. Switching from sandwich to half-sandwich complexes decreased the electrochemical potentials drastically, showing better stabilization of the cerium(IV) center in the case of Cp*Ce(OR)3 than in the case of Cp*2Ce(OR)2. Enhanced stabilization of the cerium +IV oxidation state could be further demonstrated in the series alkoxy > siloxy > aryloxy as well as C5Me5 > C5HMe4.

Reductive Electropolymerization and Electrochromism of Iron(II) Complex with Styrene-Based Ligand.

The benzimidazole-based ligand containing polymerizable styrene group has been prepared via condensation of picolinaldehyde derivative containing styrene moiety and benzimidazole-based hydrazine. The ligand reacted with iron(II) tetrafluoroborate and iron(II) trifluoromethanesulfonate giving red-brown complexes of Fe(II) ions of formula [FeL2]X2, where X = CF3SO3− (1) or BF4− (2). Reductive electropolymerization was used to obtain a thin layer of the polymeric complex, poly-1. Further investigation of electrochemical properties of the compound by cyclic voltammetry showed two quasi-reversible redox processes assigned to electrooxidation and electroreduction of the polymer. Spectroelectrochemical measurements confirmed that the polymer undergoes the color changes during oxidation and reduction process. The polymer in its neutral state (Fe(II)) is yellow and it exhibits absorption band at 370 nm, after oxidation to Fe(III) state absorption band shifts to 350 nm and the polymer is almost colorless. While the metal ions are reduced to Fe(I) absorption band at around 410 nm has been observed and the polymer changed its color to intense yellow. The stability of the polymer during multiple oxidation/reduction cycles has also been investigated.

Redox Property Tuning in Bipyridinium Salts.

Bipyridinium salts are currently very popular due to their perspective applications in redox flow batteries. Hence, we designed and prepared a series of bipyridiniums based on 2,2′-, 3,3′-, and 4,4′-bipyridine and 2,2′-bipyrimidine. The straightforward synthesis utilizes commercially or readily available starting compounds and their direct N-alkylation, mostly using 1,3-propanesultone. All eleven target derivatives with systematically evolved structure were investigated by cyclic voltammetry, which allowed elucidating thorough structure-property relationships. The electrochemical behavior depends primarily on the parent scaffold, type of N-alkylation, number of quaternized nitrogen atoms, planarity, counter ion as well as the used media. Two derivatives featuring quasi-reversible redox processes were further tested on rotating disc electrode and in a flow battery half-cell. 4,4′-Bipyridinium derivative bearing two sultone residues showed better performance and stability in the flow half-cell with small capacity decays of 0.09/0.15% per reduction-oxidation cycle, based on the number of the utilized redox processes (one/two).

Comparative study of the antioxidant and antibacterial activities of Rumex abyssinicus with commercially available Zingiber officinale and Curcuma longa in Bahir Dar city, Ethiopia

BackgroundRumex abyssinicus (RA) is one of indigenous plants to Ethiopia having traditional values during butter refinement in rural areas. This paper presents a comparative study of the antioxidant and antibacterial activities of RA sample extract to that of Zingiber officinale (ZO) and Curcuma longa (CL).MethodsPhytochemical screening tests were, first, done using different confirmatory tests prior to quantitative determinations. Quantitative determinations were then conducted—the total phenolic content by the Prussian blue method, total flavonoid content by the aluminum colorimetric assay, and antioxidant activity by the reducing power assay and the cyclic voltammetry technique.ResultsAll of the samples showed positive tests, with different intensities, for the presence of phenolics, flavonoids, glycosides and tannins, but not for alkaloids. The total phenolic content, the total flavonoid content and the antioxidant activities of RA (in mg/100 g dry weight) were found to be 319.208 ± 15.997, 113.252 ± 1.702 and 45.632 ± 2.026, respectively. On the other hand, both oxidation and reduction peaks were observed in the cyclic voltammetry analysis of the herbs, showing a quasi-reversible redox process of their phenolic compounds. The determination of the inhibition zones (in mm) of ethanol extract of RA was found to be 20.33 ± 0.58, 21.67 ± 0.58, 19.17 ± 0.29, 18.17 ± 0.29, and 21.67 ± 0.58 against Staphylococcus aureus, MRSA, Streptococcus pneumonia, Escherichia coli, and Shigella flexneri bacteria strains, respectively.ConclusionThe substantial antioxidant and antibacterial activities of RA compared to ZO and CL indicate that the traditional use of the herb to refine butter and keep it safe longer without rancidity formation and other traditional medicinal practices can be attributed to both its antioxidant and antibacterial activities.

A new two-dimensional covalent organic framework with intralayer hydrogen bonding as supercapacitor electrode material

Abstract A new two-dimensional covalent organic framework (DBT-MA-COF) is designed and synthesized via Carbon–Nitrogen coupling reaction by using 2,5-dibromothiophene (DBT) and melamine (MA) as the monomers. The C−Hˑ N intralayer hydrogen bonding exists in the structure of DBT-MA-COF so that a plane rigid structure can be maintained. The material exhibits a quasi-reversible redox process caused by triazine units and the transformation of the quinone and aromatic structures to make the DBT-MA-COF possess pseudocapacitive characteristics. DBT-MA-COF has high heteroatom content for the existence of triazine and thiophene units, which can accelerate the transfer of electrolyte ions on the surface of DBT-MA-COF electrode and improve the solution conductivity of the material. The assembled asymmetric supercapacitor DBT-MA-COF//C-CTS ASC has a high energy density of 32.1 W h kg−1 with the power density of 800 W kg−1. The cycle life of the device is excellent which can reach 83% even after 30,000 continuous galvanostatic charge-discharge cycles. The strategy in this work provides a line of thinking to design and prepare new COFs used as long life and pseudocapacitive supercapacitor materials.

Synthesis, structural and electrochemical characterization of novel ferrocene-containing tetrahydropyrimidin-2(1H)-ones

Herein, we report an easy performable method for the synthesis of ferrocene-containing tetrahydropyrimidin-2(1H)-ones starting from the corresponding 3-arylamino-1-ferrocenylpropan-1-ols and sodium cyanate (NaOCN) in the presence of glacial acetic acid. The protocol is included an intramolecular cyclization of an in situ generated 1,3-hydroxyurea. The scope of the reaction towards eleven ferrocene-containing 1,3-amino alcohols has been explored and the targeted 1-aryl-4-ferrocenyltetrahidropyrimidin-2(1H)-ones were obtained in good to high yields (up to 93%). All products have been isolated in high purity >95%. In addition, we have provided a detailed structural characterization of the new compounds, which has been performed by IR and NMR spectroscopy. The single-crystal X-ray diffraction analysis was successfully performed on three representative examples, as well as elemental analysis. Moreover, molecular structure properties and intermolecular interactions of these three structures have been compared and analyzed in detail. Electrochemical properties of products were investigated by cyclic voltammetry. This investigation revealed the quasi-reversible one-electron redox process.

Synthesis, characterization, ab initio quantum chemical calculations and molecular docking studies of Se bearing phenoxo-bridged bimetallic Ni(II) complexes

In this paper, we report the reactivity of Ni(dppe)Cl2; dppe = bis(diphenylphosphino)ethane, with phenol based selenium bearing macroacyclic Schiff bases, 2,6-bis({N-[2-(phenylselenato)ethyl]} benzimidoyl)-4-methylphenol and 2,6-bis({N-[3-(phenylselenato)propyl]}benzimidoyl)-4-methylphenol. The reaction of Ni(dppe)Cl2 with these Se2N2O ligands in 1:1 M ratio yield [{(PhC = NCH2CH2SePh)(C6H2(O)(4-CH3)(PhCO)}2Ni2Cl2], 1 and [{(PhC = NCH2CH2CH2SePh) (C6H2(O)(4-CH3)(PhCO)}2Ni2Cl2], 2 as suggested by analytical and spectroscopic data of respective complexes and supported by single crystal X-ray crystallography of phenylseleno(ethyl)amine hydrochloride. In both of these bimetallic complexes, one arm of the ligand undergoes hydrolysis at the CN bond and the 1,2-bis(diphenylphosphenoethane) moiety of 1,2-bis(diphenylphosphino)ethanenickel(II) chloride is displaced by stronger chelating donors; nitrogen and oxygen of the ligands. Two molecules of the partially hydrolyzed ligand coordinate to two Ni(II) through azomethine nitrogen, benzoyl oxygen and the phenolic oxygen. The phenolic oxygen bridges the two Ni(II) ions. Each nickel is bonded to one chloride. Nickel adopts square pyramidal coordination geometry with trans-NiNO3Cl core as evaluated by spectroscopic data and ab initio quantum chemical calculations at Hartree-Fock level. The cyclic voltammograms of complex 1 and 2 show metal centered two electron quasi-reversible redox processes. Molecular docking study of the ligands L1H and L2H and complexes 1 and 2 with DNA revealed non-covalent interaction and bind at active sites of B-DNA. The minimum calculated binding energy is −6.44 kcal/mol in complex 2.

Novel synthesis of poly(2-acryloyloxyethyl ferrocenecarboxylate) as quasi-reversible redox-active gel polymer electrolytes

In this research, the electrochemical behavior of poly(2-acryloyloxyethyl ferrocenecarboxylate) (PAEFc) synthesized via an atom transfer radical polymerization (ATRP) strategy was investigated in a series of tetrabutylammonium perchlorate (TBAP)/acetonitrile vs. Ag/AgNO3 system. In comparison, series of PAEFc electrolyte with specific molecular weight and depositing concentration were analyzed via cyclic voltammetry (CV) method. Furthermore, chronocoulometry (CC) technology has been employed on the dynamic electron/mass transfer mechanism and the determination of kinetic parameters (diffusion coefficients, reaction rate constant, etc.). Finally, it is demonstrated that anodic and cathodic process of PAEFc was controlled by diffusion and adsorption–diffusion, respectively. Meanwhile, the kinetic parameters of the typical quasi-reversible redox process were obtained, of which the apparent activation energy (Ea) and pre-exponential factor (A) were 121.38 kJ mol−1 4.28 × 1018 s−1, respectively.

Chloride functionalized carbon nanotube sponge: High charge capacity and high magnetic saturation

A chloride functionalized carbon nanotube sponge (CNS) was produced using the aerosol-assisted chemical vapor deposition method. The CNS was grown using 1,2-dichlorobenzene and ferrocene as precursors. The chloride functionalized CNS was characterized by scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction, vibrating sample magnetometry and cyclic voltammetry (CV). The CNS is formed by entangled multiwalled carbon nanotubes (MWCNTs) of 32 nm diameter with Fe3C nanowires inside. FTIR and XPS demonstrated that the surface of MWCNTs hosts functional groups such as trichloromethyl (CCl3), chloride (C–Cl), carbonyl (CO), carboxylic (COOH), and phenolic (C–O). Magnetic measurements at 300 K revealed a saturation magnetization of 192.7 emu/g and a coercive field of 502 Oe. CV studies show that the iron species and 3.2% oxygen over the surface of CNS leads to a quasi-reversible redox process and hydroquinone/quinone redox process, respectively. High charge capacity is correlated with chloride functionalities. The CNS could be used as a magnetic oil-spill cleaner, anodes in lithium-ion batteries, or specific magnetic-catalyst. Density functional theory calculations reveal the structural stability and charge transfer over chloride functional groups anchored to the surface of MWCNTs.

Electrochemical study of Nickel Oxide (NiO) nanoparticles from cactus plant extract

ABSTRACTP-type NiO powders with an average crystallite size of 16 nm as shown by x-ray diffraction analysis were produced via biosynthesis using cactus plant extract. SEM showed that the NiO powders consisted of particles with sizes in the 20-35 nm range. A cyclic voltammetric study of the NiO nanopowders showed a quasi-reversible redox processes with the NiO powder showing potential for pseudo capacitance. Through these findings the use of natural Cactus extracts is hereby shown to be a cost-effective and environmentally friendly alternative for preparing Nickel oxide nanosized powders that can be of use in a variety of energy storage applications.

Induced apoptosis against U937 cancer cells by Fe(II), Co(III) and Ni(II) complexes with a pyrazine-thiazole ligand: Synthesis, structure and biological evaluation

Complexes of iron(II), cobalt(III) and nickel(II) with 4-(4-methoxyphenyl)-2-(2-(1-(pyrazin-2yl)ethylidene)hydrazinyl)thiazole (PyztH) have been synthesized and characterized by elemental analyses, spectroscopic methods, CV measurements and a DFT study. The crystal and molecular structures were determined by the X-ray diffraction method. The complexes have the compositions [Fe(Pyzt)2]Br2 (1), [Co(Pyzt)2]PF6 (2) and [Ni(Pyzt)(PyztH)]ClO4 (3), with an approximate octahedral environment around the metal centre with NNN donor atoms from the two coordinating ligands. The complexes belong to the triclinic crystal system and crystallize in the space group P-1. Complex 1 is stabilized by strong hydrogen bonds, whereas the stability of complexes 2 and 3 is associated to π–π stacking interactions. The chemical reactivity, frontier orbital picture and energies of the HOMO and LUMO of the complexes have been estimated by a DFT study. The complexes are redox active species and respond with a quasi-reversible redox process. The cytotoxicity of the complexes was tested against U-937 human monocytic cells and shows IC50 values of 132 (for 1), 45 (for 2) and 162 µM (for 3). A LDH release assay indicates that 2 and 3 show apoptosis in the tumour cell. Complex 2 induces apoptosis by disrupting the mitochondrial membrane potential and homeostasis leading to cytotoxicity, as envisaged by PARP cleavage. Complexes 1, 2 and 3 show high binding constants (2.01 × 106 M−1 for 1, 1.18 × 107 M−1 for 2 and 2.90 × 107 M−1 for 3) with CTDNA which attest the groove binding nature of the complexes with DNA. The compounds also exhibit a remarkable zone of inhibition against specific tested bacterial and fungal strains. Based on the results, the cobalt complex (2) shows the best antitumor and antimicrobial activity among the complexes under investigation.

Systematic approaches to improving the performance of polyoxometalates in non-aqueous redox flow batteries

Polyoxometalates have been explored as multi-electron active species in both aqueous and non-aqueous redox flow batteries. Although non-aqueous systems in principle offer a wider voltage window for redox flow battery operation, realization of this potential requires a judicious choice of solvent as well as polyoxometalate properties. We demonstrate here the superior performance of N,N-dimethylformamide (DMF) compared to acetonitrile as a solvent for redox flow batteries based on Li3PMo12O40. This compound displays two 1-electron transfers in acetonitrile but can access an extra quasi-reversible 2-electron redox process in DMF. A cell containing 10 mM solution of Li3PMo12O40 in DMF produced a cell voltage of 0.7 V with 2-electron transfers (State of Charge = 60%) and showed a good cyclability. As a means to boost energy density, operation of the redox flow battery at a higher concentration of 0.1 M Li3PMo12O40 produced cells with cell voltage of 0.6 V in acetonitrile and a cell voltage of 1.0 V in DMF; both showed excellent coulombic efficiencies of more than 90% over the course of 30 cycles. Energy density was also increased by employing an asymmetric cell with different polyoxometalates on each side to extend cell voltage. Li6P2W18O62 exhibited 3 quasi-reversible 2-electron transfers in the potential range between −2.05 V and −0.5 V vs. Ag/Ag+. 10 mM Li6P2W18O62/Li3PMo12O40 in DMF produced a cell with cell voltage of 1.3 V involving 4-electron transfers (State of Charge = 50%) with coulombic efficiency of nearly 100% and energy efficiency of nearly 70% throughout the test with more than 20 cycles. These promising results demonstrate proof-of-concept approaches to improving the performance of polyoxometalates in non-aqueous redox flow batteries.

Crystal structure, spectroscopic studies, DFT calculations, cyclic voltammetry and biological activity of a copper (II) Schiff base complex

Abstract Herein we describe the chemical synthesis of a novel tetradentate Schiff base ligand (H2L), bridged with a pyridine, and its corresponding mononuclear copper complex (Cu(II)L). H2L, derived from the condensation of 2,3-diaminopyridine and 5-bromosalicylaldehyde, and Cu(II)L were structurally confirmed by routine spectral techniques, UV–Vis, FT-IR, 1H NMR, MS and elemental analysis. Single crystal X-ray diffraction analysis of Cu(II)L complex showed a monoclinic system with P21/C space group and Z = 4 molecules per unit cell. The characterization data of the complex revealed strong coordination via azomethine nitrogen (N) and bromo-phenolate oxygen (O). Moreover, the experimental parameters were found in line with the theoretical parameters. The conductivity measurement showed a non-electrolytic nature of the complex and the electrochemical behavior exhibits two quasi reversible redox processes. In-vitro antimicrobial studies on the synthesized compounds revealed a significant activity of the complex on some bacteria strains than the free ligand. DFT calculations were fully optimized using B3LYP and confirmed practical electrochemical and antibacterial results.

Tetrahedral nickel(ii) and cobalt(ii) bis-o-iminobenzosemiquinonates.

The new bis-o-iminobenzosemiquinonate nickel and cobalt complexes (imSQt-Bu)2M (M = Ni (1), Co (2)), where imSQ is a radical anion of 4,6-di-tert-butyl-N-(tert-butyl)-o-iminobenzoquinone, were synthesized and characterized in detail. The molecular structures of 1 and 2 have been established by single-crystal X-ray analysis. The metal atoms in 1 and 2 have a distorted tetrahedral environment, and the dihedral angles between the planes of two radical imSQ ligands are approximately 80° in both complexes. According to the structural and spectroscopy data along with magnetic susceptibility measurements the electronic structure of the complexes should be interpreted definitely as a high spin metal center NiII (d8, S = 1) in 1 and CoII (d7, S = 3/2) in 2 bonded with two o-iminobenzosemiquinonate radicals (Srad = 1/2). The strong antiferromagnetic metal-ligand spin interactions in both complexes lead to the observed St = 0 and St = 1/2 ground states in 1 and 2, respectively. The computational DFT UB3LYP/6-311++G(d,p) studies performed on 1 and 2 are in good agreement with experimental data. Complexes 1 and 2 have similar electrochemical properties. The electrochemical reduction of the complexes includes two quasi-reversible one-electron-transfer waves in the cathodic region corresponding to the formation of the anions [M(AP)2]2- and [(imSQ)M(AP)]1- (AP - dianion of 4,6-di-tert-butyl-N-(tert-butyl)-o-iminobenzoquinone), while in the anodic region only one quasi-reversible redox process was registered. All redox processes are shown to be ligand-based.

Synthesis, X-ray structure, physicochemical properties and anticancer activity of mer and fac Ru(iii) triphenylphosphine complexes with a benzothiazole derivative as a co-ligand.

Two mononuclear ruthenium(iii) mer- and fac-isomers of the formula [RuCl3(PPh3)(dmpbt)] (where PPh3 = triphenylphosphine, dmpbt = 2-(3,5-dimethylpyrazoll-yl)benzothiazole) have been synthesised from the reaction of [RuCl3(PPh3)3] with a bidentate ligand - dmpbt. Appropriate reaction conditions allowed obtaining the two isomers separately without separation techniques. X-ray crystallography has determined the crystal and molecular structures of the new complexes. mer-Ru(iii) (1) crystallised in the monoclinic P2(1)/n group, and fac-Ru(iii) (2, 2') in the triclinic P1[combining macron] space group. The composition of the ruthenium coordination sphere was confirmed and characterised using spectroscopic techniques (FT-IR, UV-vis and EPR), elemental analysis and mass spectrometry (MS-FAB). The structures of the complexes obtained were analysed using X-ray and other spectroscopic methods (IR and UV-vis). The electrochemical properties of the ligand and the complex compound were identified using cyclic voltammetry, determining the potential and charge of faradaic processes. Both isomers are redox active and display quasi-reversible metal centered redox processes for the Ru(iii)/Ru(ii) pair. Moreover, preliminary tests of their biological activity were performed. The cytotoxicity of these compounds has been tested for human lung carcinoma (A549), chronic myelogenous leukemia (K562), human cervix carcinoma (HeLa) cells, acute lymphoblastic leukemia (MOLT-4), human breast adenocarcinoma cell line (MCF-7) and normal human umbilical vein endothelial cells (HUVEC). The ability to induce apoptosis has been demonstrated in caspase 3/7 activity assay. In addition, the lipophilicity of both isomers was described by a partition coefficient, log P, values of which were estimated by the shake-flask method. The interesting and promising preliminary results of the biological and chemical activities of the new octahedral mer/fac Ru(iii) complexes motivate further in vitro and in vivo studies.