Quasi-reversible Process Research Articles

Al electrodeposition from chloroaluminate ionic liquid

Cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy were used to investigate the mechanism of Al electrodeposition for an ionic liquid with a 2∶1 molar ratio of AlCl3/[EMIM]Br (1-methyl-3-ethyl imidazolium bromide) at room temperature 25±1°C. Results indicated that the Al electrodeposition from this ionic liquid is a quasi-reversible process. Instantaneous nucleation with diffusion controlled growth of the Al electrode was demonstrated. The constant phase element was present in the electrical double layer, with α = 0·37. The kinetic complications during the reaction may be attributed to the controlled cooperative processes of electron transfer and mass transport. The potential effects on the characteristics of Al deposits were evaluated by scanning electron microscopy and X-ray diffraction. Granular Al deposits could be obtained at a potential higher than −0·45 V. Cubic featured Al deposits were obtained within the range of −0·56 to −0·88 V. The rough deposits began to show dendritic morphologies at a potential less than −1·05 V.On a utilisé les techniques électrochimiques de la voltampérométrie cyclique, de la chronoampérométrie et des spectres d’impédance électrochimique pour examiner le mécanisme d’électrodéposition de l’aluminium (Al) à partir d’un liquide ionique d’AlCl3/[EMIM]Br de 2∶1 (rapport molaire) à la température de la pièce (25±1°C). Les résultats indiquaient que l’électrodéposition de l’Al à partir de ce liquide ionique était un procédé quasi réversible. On a mis en évidence la nucléation instantanée avec croissance contrôlée par diffusion de l’électrodéposition de l’Al. L’élément à phase constante (EPC) qui se produisait dans la couche électrique double montrait une valeur de α = 0·37. On peut attribuer les complications cinétiques pendant la réaction aux procédés contrôlés en coopérative du transfert d’électron et du transport de masse. On a évalué les effets du potentiel sur les caractéristiques des dépôts d’Al au moyen de la microscopie électronique à balayage (SEM) et du diffractomètre à rayons X allemand (XRD). On a également observé que l’on pouvait obtenir un dépôt granuleux d’Al à un potentiel plus élevé que –0·45 V. On a obtenu des dépôts d’Al à caractéristique cubique dans la gamme de potentiel de –0·56 à ∼ −0·88 V. Les dépôts obtenus à un potentiel de moins que –1·05 V devenaient rugueux et commençaient à montrer des morphologies dendritiques.

Electrochemical behavior of tungsten in (NaCl–KCl–NaF–WO3) molten salt

The electrochemical reaction mechanism and electrocrystallization process of tungsten in the NaCl–KCl–NaF–WO3 molten salt were investigated at 973 K (700 °C) by means of cyclic voltammetry, chronopotentiometry, and chronoamperometry techniques. The results show that the electrochemical reaction process of tungsten in the NaCl–KCl–NaF–WO3 molten salt system is a quasi-reversible process mix-controlled by ion diffusion rate and electron transport rate. Tungsten ion in this system is reduced to W(0) in two steps. The electrocrystallization process of tungsten is found to be an instantaneous, hemispheroid three-dimensional nucleation process and the tungsten ion diffusion coefficient of 2.361 × 10−4 cm2·s−1 is obtained at experimental conditions.

Simultaneous Determination of Hydroquinone and Catechol at Poly-Histidine Film Modified Glassy Carbon Electrode

The poly-histidine (poly-HTD) film was prepared at glassy carbon electrode by electropolymerization, and its electrochemical behavior was investigated by cyclic voltammetry. Results show that the behavior of this poly-HTD film is in good agreement with quasi-reversible process characteristic. At low scan rates, the electronic transfer process of electrode reaction is controlled by surface process. At this poly-HTD film modified electrode, an excellent electrocatalytic ability towards the redox of hydroquinone (HQ) and catechol (CC) with decrease of the overpotential and improvement of the redox peak currents was found. Differential pulse voltammetry was used for the simultaneous determination of HQ and CC in their mixture, and the peak-to-peak separation ΔEpfor HQ and CC was 110 mV. Therefore, this polymer modified electrode can be used for the simultaneously selective determination of HQ and CC without interference with each other.

Redox properties of cobalt(II) complexes with azole-pyridines

We report nine new homoleptic octahedral cobalt(II) complexes [Co(N^N)3]2+ and [Co(N^N^N)2]2+ with bidentate or tridentate azole-pyridine ligands (where azole is 1,2,4-triazole or a substituted pyrazole). The complexes are air- and moisture-stable solids of pale pink to pale brown color that exhibit quasi-reversible redox processes in polar organic solvents. By changing azole heterocycle and by adding methyl groups, we tune redox potentials of the complexes from 0.05 to 0.5V for the Co(III/II) couple (its cyclic voltammogram depends on the electrode history) and from −1.08 to −1.57V for the Co(II/I) couple to give a redox gap of 1.37–1.82V. Replacing a pyrazole with electron-deficient 1,2,4-triazole strongly positively shifts redox potentials of the complexes; in contrast, adding electron-donor methyl groups shifts the potentials negatively.

Application of poly(acridine orange) and graphene modified carbon/ionic liquid paste electrode for the sensitive electrochemical detection of rutin

A carbon/ionic liquid paste electrode (CILPE) prepared by 1-hexylpyridinium hexafluorophosphate as the binder was used as the substrate electrode. A layer of graphene oxide (GO) film was cast on CILPE surface (GO/CILPE) and the electropolymerization of acridine orange (AO) on electrode was further realized by cyclic voltammetry in the potential range from −1.40V to 1.40V, which could simultaneously reduce GO to graphene (GR) electrochemically. The fabricated PAO-GR/CILPE exhibited good electrochemical performances with higher conductivity and lower electron transfer resistance. Electrochemical behaviors of rutin were further investigated on the modified electrode in 0.1mol/L pH 2.0 phosphate buffer solution by cyclic voltammetry with a pair of well-defined redox peaks appeared. The peak-to-peak separation (ΔEp) was calculated as 0.076V, which proved a fast quasi-reversible electron transfer process and the electrochemical parameters of rutin on PAO-GR/CILPE were calculated. Under the optimal conditions, the linear relationship between the oxidation peak current of rutin and its concentration was obtained in the range from 0.03 to 800.0μmol/L with the detection limit as 8.33nmol/L (3σ). The PAO-GR/CILPE showed good selectivity, stability and reproducibility, which was further applied to detect rutin tablet samples with satisfactory results.

Graphene–PEDOT:PSS on screen printed carbon electrode for enzymatic biosensing

In this work, a highly sensitive enzyme-based biosensor is developed based on graphene–poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid (GP-PEDOT:PSS) modified screen printed carbon electrode (SPCE) for electrochemical detection of glucose. GP-PEDOT:PSS nanocomposite synthesized by one-step electrolytic exfoliation is drop-coated on SPCE and glucose oxidase (GOD) enzyme is then immobilized on GP-PEDOT:PSS by glutaraldehyde cross linking. Electron microscope characterization confirms the presence of multi-layer graphene sheets and the appearance of smooth and long microstripe structure of GOD on the electrode surface. Direct electrochemistry of GOD at the GP/PEDOT:PSS electrode is observed by cyclic voltammetry and graphene plays the main role in a quasi-reversible redox process. GOD/GP-PEDOT:PSS electrode exhibits a high amperometric sensitivity of 7.23μA/mM, which is about 13 times higher than that of GOD/PEDOT:PSS but has a relatively narrow linear dynamic range of ∼20–900 μM. Moreover, GOD/GP-PEDOT:PSS offers a very low detection limits (3S/N) of ∼0.3 μM which is better or comparable to other recent reports of highly sensitive glucose biosensors. Furthermore, the sensor has good stability with only 30% loss of enzyme activity after 30days.

Electrochemical behavior of progesterone at an ex situ bismuth film electrode

An ex situ bismuth film electrode (BiFE) was used for the electrochemical study of the hormone progesterone. Two peaks were observed by cyclic voltammetry, at −1.68V and −1.47V, respectively, associated with the reduction and oxidation reactions of progesterone in 0.1molL−1 Britton–Robinson solution at pH 12.0, in agreement with a quasireversible electrode process. In relation to the mechanism, an adsorption-controlled reaction rate with one electron involved in the electrochemical step was observed. Square-wave adsorptive stripping voltammetry was used for the analytical procedures after accumulation of the progesterone for 60s at −1.0V. A peak current at −1.63V related to the reduction of progesterone was obtained, which increased linearly with the hormone concentration in the range of 0.40–7.90μmolL−1 (R2=0.9983). The limit of detection attained was 0.18μmolL−1. The method was applied in the determination of progesterone in four pharmaceutical samples with satisfactory results being obtained compared with a spectrophotometric method.

Synthesis, Spectra, and Electron-Transfer Reaction of Aspartic Acid-Functionalized Water-Soluble Perylene Bisimide in Aqueous Solution

An aspartic acid-functionalized water-soluble perylene bisimide, N,N'-di(2-succinic acid)-perylene-3,4,9,10-tetracarboxylic bisimide (PASP) was synthesized and characterized. It has absorbance maximum A(0-0) and A(0-1) at 527 and 498 nm (ε ≈ 1.7 × 10(4) L cm(-1) mol(-1)) respectively in pH 7.20 HEPES buffer. Two quasi-reversible redox processes with E1/2 at -0.17 and -0.71 V (vs Ag/AgCl) respectively in pH 7-12.5 aqueous solutions. PASP can react with Na2S in pure aqueous solution to form monoanion radical and dianion species consecutively. PASP(-•) has EPR signal with g = 1.998 in aqueous solution, whereas PASP(2-) is EPR silent. The monoanion radical formation is a first-order reaction with k = 8.9 × 10(-2) s(-1). Dianion species formation is a zero-order reaction and the rate constant is 4.3 × 10(-8) mol L(-1) s(-1). The presence of H2O2 greatly increases the radical formation rate constant. PASP as a two-electron transfer reagent is expected to be used in the water photolysis.

Sensitive voltammetric responses and mechanistic insights into the determination of residue levels of endosulfan in fresh foodstuffs and raw natural waters

This paper describes the electroanalytical study of the organochlorine pesticide endosulfan (EDS) using square-wave voltammetry. The electrochemical behaviour showed a quasi-reversible process on a hanging mercury drop electrode (HMDE) in acid medium attributed to reduction of the carbon–chlorine bond. The constant of change transfer obtained for this process was 354s−1. The redox mechanism was confirmed by quantum-chemical (Density Functional Theory, DFT) studies. The optimised experimental and voltammetric parameters were 0.04molL−1 Britton–Robinson buffer (pH4.0), the pulse potential frequency of 200s−1, the amplitude of the pulse of 20mV, and the height of the potential step of 4mV. Analytical parameters such as linearity range, equation of the analytical curves, correlation coefficients, detection and quantification limits, recovery values, precision, and accuracy were obtained. The procedure was applied to the analysis of pesticide in complex samples: sugar cane, tomato, and raw natural waters. The recovery values demonstrated that the proposed methodology is suitable for determining EDS in such samples. The results indicated that the proposed procedure is stable and sensitive, with good reproducibility, and no complex procedure was necessary for sample preparation. The development of this electroanalytical procedure is therefore appropriate, as it provides adequate sensitivity and reliable methodology.

Electrochemical Properties of GaCl<sub>3</sub> in Ionic Liquid [C<sub>2</sub>mim][GaCl<sub>4</sub>

Under dry argon atmosphere, the colourless and transparent ionic liquid [C2mim][GaCl4] was synthesized. Using [C2mim][GaCl4] as solvent, a solution of GaCl3with molarity 5.227×10-3 mol/cm3 was prepared at 303.15 K and there is a equilibrum between the solute and the solvent: GaCl3+ [C2mim][GaCl4] → [C2mim][Ga2Cl7]. The cyclic voltammogram of the solution had been carried out relative to Al/Al3+reference electrode, with GC working electrode and Ga counter electrode, with various scan rates from 30 to 700mV/s, in a temperature range of 303.15 to 343.15 K, respectively. The results indicated that (1) there were two processes: Ga(Ⅲ)→Ga(I)→Ga(0), which corresponded to the double reduction peaks in the cyclic voltammogram; (2) the first reduction process was a diffusion controlled and quasi-reversible process. Plotting current density of the peak vs the square root of scan rate, a series of straight lines were obtained, then the diffusion coefficients were obtained according to Randles-Sevcik equation in various temperature. The values of diffusion coefficient were fitted to Arrhenius equation with least-square method and value of diffusion activation energy, ED = 41.5 kJ/mol, was obtained from Arrhenius slope.

Rapid electrochemical detection of ferulic acid based on a graphene modified glass carbon electrode

A graphene nanosheet modified glassy carbon electrode (GN/GCE) is proposed as a voltammetric sensor for ferulic acid with good sensitivity, selectivity and reproducibility. The sensor oxidizes ferulic acid in a surface-confined and quasi-reversible process, as revealed by cyclic voltammetry. The results show more favorable electron transfer kinetics than for a bare glassy carbon electrode (GCE). The linear response of the sensor is from 5 × 10−7 to 5 × 10−5 M with a detection limit of 2 × 10−7 M (S/N = 3). Graphene, as a single nanosheet, shows more favorable electrochemical activity and should be a more robust and advanced carbon electrode material, which provides a promising platform for electrochemical sensors and biosensors. The method was successfully applied to the detection of ferulic acid in pharmaceutical tablets with satisfactory results.

Synthesis, Structure, NMR Spectroscopy, and Electrochemistry of the Sterically Congested Triarylarsine Dipp3As: EPR Characterization of its Radical Cation

The synthesis, NMR spectroscopy, single-crystal X-ray structure, and solution electrochemistry of the new compound [2,6-{CH(CH3)}2C6H3]3 As, abbreviated as Dipp3As, is reported. The molecule, prepared by reaction of AsCl3 with a pre-formed aryl copper reagent, Dipp4Cu4, crystallizes in the hexagonal space group R3 as a racemic twin. The sum of angles around As, ∑∠{CAsC}, is 329.13(3)° in the X-ray structure and 329.17° from an R-B3LYP/6-31G(d,p) hybrid density functional theory calculation. The aromatic rings are quite distorted with both the ipso carbon and especially the As atom significantly out of plane by 0.503(3) Å. The ambient temperature NMR spectrum fits for C3 symmetry implying that inversion is slow on the NMR timescale. Cyclic voltammetry on a glassy carbon electrode in CH2Cl2 with 0.4 M [nBu4N][PF6] over scan rates of 0.05–0.8 V s–1 and temperatures of 22 ± 2°C produced one quasi-reversible process with Em1 = +0.43 V at a scan rate of 0.20 V s–1 and a second irreversible process with a peak potential of +1.45 V (v. Fc+/0). The diffusion coefficient has been measured as 3.3 ± 0.1 × 10–6 cm2 s–1 in CH2Cl2 solution containing 0.4 M [nBu4N][PF6]. Chemical oxidation with AgPF6 in CH2Cl2 in degassed solutions in sealed vessels allowed for recording of characteristic EPR spectra; at 293 K, a (75As) = 26.1 mT and g = 2.021. In frozen solution, an almost isotropic spectrum is obtained (g║ = 2.000 mT and g⊥ = 2.003 mT) and the hyperfine splitting constants are a║ = 47.9 and a⊥ = 19.0 mT, leading to an estimate for the structure being slightly pyramidal with ∑∠{CAsC} ≈ 351°.

Synthesis, characterization and catalytic activity of copper(ii) complexes containing a redox-active benzoxazole iminosemiquinone ligand

A tridentate benzoxazole-containing aminophenol ligand HL(BAP) was synthesized and complexed with Cu(II). The resulting Cu(II) complexes were characterized by X-ray, IR, UV-vis-NIR spectroscopies, and magnetic susceptibility studies, demonstrating that the ligand is oxidized to the o-iminosemiquinone form [L(BIS)](-) in the isolated complexes. L(BIS)Cu(II)Cl exhibits a distorted tetrahedral geometry, while L(BIS)Cu(II)OAc is square pyramidal. In both solid state structures the ligand is coordinated to Cu(II)via the benzoxazole, as well as the nitrogen and oxygen atoms from the o-iminosemiquinone moiety. The chloride, or acetate group occupies the fourth and/or fifth positions in L(BIS)Cu(II)Cl and L(BIS)Cu(II)OAc, respectively. Magnetic susceptibility measurements indicate that both complexes are diamagnetic due to antiferromagnetic coupling between the d(9) Cu(II) centre and iminosemiquinone ligand radical. Electrochemical studies of the complexes demonstrate both a quasi-reversible reduction and oxidation process for the Cu complexes. While L(BIS)Cu(II)X (X = Cl) is EPR-silent, chemical oxidation affords a species with an EPR signal consistent with ligand oxidation to form a d(9) Cu(II) iminoquinone species. In addition, chemical reduction results in a Cu(II) centre most likely bound to an amidophenoxide. Mild and efficient oxidation of alcohol substrates to the corresponding aldehydes was achieved with molecular oxygen as the oxidant and L(BIS)Cu(II)X-Cs2CO3 as the catalyst.

Synthesis, spectral, and structural characterizations of imidazole oxalato molybdenum(iv/v/vi) complexes

Substitutions of trans-Na(Him)[Mo(2)O(4)(ox)(2)(H(2)O)(2)]·H(2)O (1) and trans-(Him)(2)[Mo(2)O(4)(ox)(2)(H(2)O)(2)] (2) with imidazole result in the formation of the mixed-ligand molybdenum complexes cis-Na(2)[Mo(2)O(4)(ox)(2)(im)(2)]·4.5H(2)O (3), cis-K(2)[Mo(2)O(4)(ox)(2)(im)(2)]·3H(2)O (4), respectively (H(2)ox = oxalic acid; im = imidazole). Further reduction of cis-K(2)[Mo(2)O(4)(ox)(2)(im)(2)]·3H(2)O (4) gives a trinuclear molybdenum(IV) complex K(Him)[Mo(3)O(4)(ox)(3)(im)(3)]·3H(2)O (5), which contains an incomplete cubane cluster [Mo(IV)(3)O(4)](4+). Two novel trinuclear mixed-valence imidazole compounds [Mo(3)O(8)(im)(4)](im)·H(2)O (6) and [Mo(3)O(8)(im)(4)]·H(2)O (7) were obtained by the reduction of (Him)(4)[Mo(8)O(26)(im)(2)] (8). Both 6 and 7 contain a novel Mo(VI)O(4)(Mo(V)(2)O(4)) center, where the [Mo(V)(2)O(4)](2+) unit is linked by [Mo(VI)O(4)](2-) anion. The Mo-Mo bond distances in 1-7 decrease with the decrease of oxidation state of molybdenum. Solid and solution NMR spectra show that imidazole molybdenum compounds 6-8 fully dissociate in solution, where solvated imidazole and imidazolium groups in 6 and 8 could be served as internal references in their solid (13)C NMR spectra. Furthermore, mixed-ligand molybdenum species 3 and 4 are stable in water. Stabilities of 3 and 4 in solution may be attributed to the strong coordination of bidentate oxalate and the formation of hydrogen bond. Dimers 2 and 4 display quasi-reversible redox process, while trimer 6 is irreversible. Bond valence calculations for 1-8 are consistent with their oxidation states of molybdenum atoms. Calculation of the oxidation state in recent structure of iron molybdenum cofactor [MoFe(7)S(9)C(R-homocit)] (FeMo-co) is 3.318.

Crystal engineering of salen type cerium complexes tuned by various cerium counterions

A series of five new salen type cerium complexes, namely [Ce(H2L)2CH3OH](PF6)3·2H2O·CH2Cl2 (1), [Ce(IV)L2] (2), [Ce(H2L)(NO3)3CH3OH] (3), [Ce2(H2L)3(NO3)6]·4H2O (4) and {[Ce(H2L)2(NO3)2](PF6)·2CH3CN}n (5) (H2L = N,N′-bis(3-methoxysalicylidene)cyclohexane-1,2-diamine), have been isolated by reactions of H2L with various cerium salts and/or NH4PF6. All complexes 1–5 have been fully characterized by elemental analysis, FT-IR spectroscopy, UV spectroscopy, powder X-ray diffraction, TG–DSC analysis, and single-crystal X-ray diffraction. X-ray crystallographical analysis reveals that complexes 1–3 are of discrete mononuclear structures, 4 is of a discrete binuclear structure, and complex 5 is of a unique quartz 3D topological structure. The electrochemical behavior of this series of salen type cerium complexes has been examined by cyclic voltammetry in acetonitrile. Cyclic voltammograms of complexes 1 and 3–5 show two quasi-reversible redox processes within the electrochemical window of acetonitrile.

Electrochemical Studies and Square Wave Voltammetry of Paracetamol at Managanese Modified Carbon Paste Electrode

A square wave voltammetry (SWV) method for the determination of trace amounts of paracetamol at carbon paste electrode modified with managanese (Mn-CPE) is proposed. The results showed that the Mn-CPE exhibited excellent electro catalytic activity to paracetamol. A quasi-reversible redox process of paracetamol at the modified electrode was obtained. The concentration of paracetamol and measuring solution pH was investigated. This electrochemical sensor shows an excellent performance for detecting paracetamol with a detection limit of 6.8×10 -10 mol.L -1 with the relative standard deviation of 2.0% (n=7). The sensor was successfully applied to the determination of paracetamol in a real sample tablets with satisfactory results.

Redox-active, near-infrared dyes based on ‘Nindigo’ (indigo-N,N′-diarylimine) boron chelate complexes

Reactions of indigo-N,N′-diarylimine (‘Nindigo’) derivatives with BF3·Et2O give mono- or bis-BF2 chelate complexes 2 or 3 respectively. The product distribution between 2 and 3 is sensitive to the auxiliary base and solvent. Although the bis-BF2 complexes 3 are isolable, they gradually decompose in solution to the corresponding mono-BF2 species 2; this process is accelerated by water. The instability of 3 is believed to be due to ring stain effects based on structural analyses of 2. Electrochemical studies of 2 reveal one quasi-reversible oxidation process and two irreversible reductions, whereas derivatives of 3 possess a reversible oxidation and two sequential reversible reductions. The electronic spectra of 2 and 3 contain intense (ε ∼ 3 × 104 M−1 cm−1) long-wavelength absorptions near 650 nm and 750 nm respectively. Both series of compounds are weakly emissive in the near-infrared. Time-dependent DFT calculations reveal the electronic transitions to be π–π* in nature.

Synthesis and study of olefin metathesis catalysts supported by redox-switchable diaminocarbene[3]ferrocenophanes

A redox-switchable ligand, N,N'-dimethyldiaminocarbene[3]ferrocenophane (5), was synthesized and incorporated into a series of Ir- and Ru-based complexes. Electrochemical and spectroscopic analyses of (5)Ir(CO)2Cl (15) revealed that 5 displayed a Tolman electronic parameter value of 2050 cm(-1) in the neutral state and 2061 cm(-1) upon oxidation. Moreover, inspection of X-ray crystallography data recorded for (5)Ir(cis,cis-1,5-cyclooctadiene)Cl (13) revealed that 5 was sterically less bulky (%V(Bur) = 28.4) than other known diaminocarbene[3]ferrocenophanes, which facilitated the synthesis of (5)(PPh3)Cl2Ru(3-phenylindenylid-1-ene) (18). Complex 18 exhibited quasi-reversible electrochemical processes at 0.79 and 0.98 V relative to SCE, which were assigned to the Fe and Ru centers in the complex, respectively, based on UV-vis and electron pair resonance spectroscopic measurements. Adding 2,3-dichloro-5,6-dicyanoquinone over the course of a ring-opening metathesis polymerization of cis,cis-1,5-cyclooctadiene catalyzed by 18 ([monomer]0/[18]0 = 2500) reduced the corresponding rate constant of the reaction by over an order of magnitude (pre-oxidation: k(obs) = 0.045 s(-1); post-oxidation: k(obs) = 0.0012 s(-1)). Subsequent reduction of the oxidized species using decamethylferrocene restored catalytic activity (post-reduction: k(obs) = up to 0.016 s(-1), depending on when the reductant was added). The difference in the polymerization rates was attributed to the relative donating ability of the redox-active ligand (i.e., strongly donating 5 versus weakly donating 5(+)) which ultimately governed the activity displayed by the corresponding catalyst.

A series of tetrabromocatecholate chelated cobalt(iii) complexes with various N-donor ancillary ligands: syntheses, crystal structures, co-crystallization, thermally induced valence tautomerism and electrochemical studies

Nine new tetrabromocatechol chelated mononuclear cobalt(III) complexes with various nitrogen-donor ancillary ligands, [Co(en)2(Br4Cat)]ClO4·0·5H2O (1) [Br4CatH2 = tetrabromocatechol, en = ethylenediamine], [Co(pn)2(Br4Cat)]ClO4 (2) [pn = propylenediamine], [Co(dpd)2(Br4Cat)]NO3·CH3OH (3) [dpd = 2,2′-dimethyl-1,3-propanediamine], [Co(amp)2(Br4Cat)]ClO4 (4) [amp = 2-aminomethylpyridine], [Co(aqn)2(Br4Cat)]NO3·CH3OH (5) [aqn = 8-aminoquinoline], [Co(phen)2(Br4Cat)]ClO4·0·5CH3OH (6) [phen = phenanthroline], [Co(bpy)2(Br4Cat)]NO3·Br4CatH2·2CH3OH (7) [bpy = 2,2′-bipyridine], [Et3NH][Co(pym)2(Br4Cat)2]·H2O (8) [pym = pyrimidine] and [Co(tren)(Br4Cat)]NO3·CH3OH·H2O (9) [tren = tris(2-aminoethyl)amine], are reported. All the complexes were characterised by various spectroscopic techniques and electrochemical methods, and their structures have been elucidated by X-ray crystallography. Structural analyses reveal that a 1 : 1 cobalt-dioxolene adduct is the exclusive product with bi- or tetradentate ancillary ligands, while for the monodentate pyrimidine ligand 2 : 1 cobalt-dioxolene is the only outcome. Importantly, an unusual co-crystallization of complex 7 with one molecule of tetrabromocatechol was observed in the crystal lattice. The electrochemical studies of all the complexes disclose quasi-reversible redox processes due to the o-dioxolene ligands, in addition to reductive responses corresponding to the reduction of the cobalt(III) centres to cobalt(II). Although in the solid state all the complexes are diamagnetic, complexes 5 and 8 undergo thermally induced valence tautomerism in solution associated with the drastic change in the optical absorption properties of the complexes in the UV-vis spectroscopy.

Cu(II), Ni(II), and Zn(II) Complexes of Salan-Type Ligand Containing Ester Groups: Synthesis, Characterization, Electrochemical Properties, andIn VitroBiological Activities

A salen ligand on reduction and N-alkylation affords a novel [N2O2] chelating ligand containing ester groups [L = diethyl-2,2′-(propane-1,3-diylbis((2-hydroxy-3-methoxy benzyl)azanediyl))diacetate]. The purity of the ligand was confirmed by NMR and HPLC chromatograms. Its Cu(II), Ni(II), and Zn(II) complexes were synthesized and characterized by a combination of elemental analysis, IR, NMR, UV-Vis, and mass spectral data, and thermogravimetric analysis (TG/DTA). The magnetic moments, UV-Vis, and EPR spectral studies support square planar geometry around the Cu(II) and Ni(II) ions. A tetrahedral geometry is observed in four-coordinate zinc with bulky N-alkylated salan ligand. The redox properties of the copper complex were examined in DMSO by cyclic voltammetry. The voltammograms show quasireversible process. The interaction of metal complexes with CT DNA was investigated by UV-Vis absorption titration, ethidium bromide displacement assay, cyclic voltammetry methods, and agarose gel electrophoresis. The apparent binding constant values suggest moderate intercalative binding modes between the complexes and DNA. The in vitro antioxidant and antimicrobial potentials of the synthesized compounds were also determined.