Electron transfer. 127 Intermediate oxidation states in the reduction of chromium(VI) with formate

When HCrO₄ ^? is reduced by formate in solutions buffered by 2-ethyl-2-hydroxybutanoic acid and its anion, chelated complexes of both Cr(IV) and Cr(V), both of them stabilized in the medium used, are formed. It appears that Cr(V) is not generated directly from the Cr(VI)-formate reaction but arises instead from oxidation of Cr(IV) by Cr(VI). When the Cr(VI)-formate reaction is allowed to go to completion in the presence of [Cl(NH₃)₅Co]²⁺, a scavenger for Cr(II), 84–86% of the Cr(VI) taken is found to be converted to Cr(II), indicating that nearly all of the reacting system proceeds through Cr(IV) and bypasses the more usual state Cr(III). Initial rates for formation of Cr(IV) lead to a rate law pointing to a transition state containing the two redox partners, two ligating carboxyl groups, and two units of H⁺. Substitution of DCO₂ ^? for HCO₂ ^? retards formation of Cr(IV) by a factor of 3.3, whereas the solvent isotope affect, rate_{D 2}O/rate_{H 2}O, favors the deuterated system by a factor of 1.4. Our observations are in accord with a sequence initiated by the ligation of HCrO₄ ^? to a chelate derived from the buffering carboxylate anion. Conversions of Cr(VI) to Cr(IV), and Cr(IV) to Cr(II) appear to entail hydride shifts from formate to the Cr(=O) function.     

Conductometric determination of cerium(III) as metavanadate

Summary Conductometric determination of Ce³⁺ has been carried out successfully at 30±0.5°C by titrating it against standard sodium metavanadate solution in 15% ethanol. An overall effect of ethanol concentration on the results has also been studied. The titration curves obtained show a sharp break at the end point and lend support to the formation of Ce(VO₃)₃. The method has the advantage of being a simple and precise titrimetric procedure for the determination of Ce³⁺ in microquantities.

---

Zusammenfassung Es wird eine einfache und genaue Methode zur konduktometrischen Bestimmung von Cer(III) beschrieben. Die Titration erfolgt mit Natriummetavanadat in 15%iger äthanolischer Lösung bei 30±0,5°C. Der Einfluß der Äthanolkonzentration auf die Ergebnisse wurde untersucht. Die Titrationskurven weisen am Endpunkt einen scharfen Knick auf und deuten auf die Bildung von Ce(VO₃)₃ hin.

     

EPR, IR and electronic spectral studies on Mn(II), Co(II), Ni(II) and Cu(II) complexes with a new 22-membered azamacrocyclic [N4] ligand

The complexes of transition metal ions with an azamacrocyclic tetradentate nitrogen donor [N4] ligand viz. 2,6,12,16,21,22-hexaaza;3,5,13,15-tetramethyltricyclo[15.3.1.1(7-11)] docosa;1(21),2,5,7,9,11(22),12,15,17,19-decaene (L) have been synthesized. All the complexes were found to have general composition M(L)X2 [where M = manganese(II), cobalt(II), nickel(II) and copper(II) and X = Cl- & NO3-]. All the complexes are characterized by the elemental analysis, molar conductance measurements, magnetic susceptibility measurements, mass, 1H NMR, IR, electronic, EPR spectral and cyclic voltammetric studies. An octahedral geometry was assigned for Mn(II), Co(II) and Ni(II) complexes and tetragonal for Cu(II) complexes. The biological actions of the ligand and complexes have been screened in vitro against many bacteria and pathogenic fungi to study their comparative capacity to inhibit the growth.     

Spectroscopic studies, cyclic voltammetry and synthesis of nickel(II) complexes with N(4), N(2)O(2) and N(4)S(2) donor macrocyclic ligands

Nickel(II) complexes of the general composition Ni(L)X(2) (where X=SCN, NO(3) and 1/2SO(4) and ligands=L(1) L(2) and L(3)) have been synthesized and characterized by elemental analyses, magnetic moments, IR, (1)H NMR, (13)C NMR and electronic spectral studies. Nickel(II) ions, such as nitrates, thiocyantes and sulphates were found to act as templates for the cyclic condensations [1+1] and [2+2] of NH(2--)C(6)H(4)--O--CH(2)--CH(2)--O--C(6)H(4)--NH(2), NH(2)--(CH(2))(2)--NH(2) and NH(2)--CH(CH(3))--CH(2)--NH(2) with C(6)H(5)--CO--CO--C(6)H(5), C(6)H(5)--CO--CH(2)--CO--C(6)H(5) and (COOH--CH(2)--CH(2))(2)S. All the complexes show magnetic moments corresponding to two unpaired electrons except [Ni(L(1))](NO(3))(2) and [Ni(L(2))](NO(3))(2) complexes which are diamagnetic. Electronic spectroscopy was used to analyse the differences between the paramagnetic and diamagnetic forms. Electrochemical properties have been studied extensively for Ni(III/II) and Ni(II/I) couples. The equilibrium between the paramagnetic and diamagnetic forms and the nickel(III/II) couple are strongly dependent on the electrolyte. It has been observed that the sulphate group coordinated selectively on the apical position of the nickel(II) centers of the compounds. The structural and electrochemical studies suggest that cooperative effects, involving coordination of sulphate to one nickel center, is responsible for the recognition of this anion. Various ligand field parameters have been calculated and discussed.     

Magnetic, electronic and electrochemical studies of mono and binuclear Cu(II) complexes using novel macrocyclic ligands

A series of new mono and binuclear copper (II) complexes [Cul]X(2)and [Cu(2)lX(2)] where 1 = L(1), L(2) and L(3) are the macrocyclic ligands. In mononuclear complexes the geometry of Cu(II) ion is distorted squareplanar and in binuclear complexes the geometry of Cu(II) is tetragonal. The synthesized complexes were characterized by spectroscopic (IR,UV-vis and ESR) techniques. Electrochemical studies of the complexes reveals that all the mononuclear Cu(II) complexes show a single quasireversible one-electron transfer reduction wave (E(pc) = -0.76 to -0.84V) and the binuclear complexes show two quasireversible one electron transfer reduction waves (E(pc)(1) = -0.86 to -1.01V, E(pc)(2) = -1.11 to -1.43V) in cathodic region. The ESR spectra of mononuclear complexes show four lines with nuclear hyperfine splittings with the observed g(11) values in the ranges 2.20-2.28, g( perpendicular) = 2.01-2.06 and A(11) = 125-273. The binuclear complexes show a broad ESR spectra with g = 2.10-2.11. The room temperature magnetic moment values for the mononuclear complexes are in the range [mu(eff) = 1.70-1.72BM] and for the binuclear complexes the range is [mu(eff) = 1.46-1.59BM].     

Facile synthesis,characterization and application of magnetic Fe3O4-coir pith composites for the removal of methyl violet from aqueous solution: Kinetics,isotherm, thermodynamics and parametric optimization

Dyes are commonly used in coloring clothes; in fertilizers, as anti-freezers, as detergents and so on. The use of such dyes has carcinogenic and genotoxic effects. These dyes require proper removal from the environment. Subsequently, a green and low-cost approach promises to adhere to sustainability of the environment while maximum removal of these toxic dyes. The present study describes removal of methyl violet (MV) dye by adsorption process magnetically separable Fe₃O₄-coir pith composites. The study was evaluated in batch system taking the optimum conditions as: pH: 7, contact time: 12 h, stirring speed: 200 rpm, concentration of dye: 100 mg/L, adsorbent weight: 3 g/L, temp.: 308 K. The central composite design approach of response surface methodology in design-expert software showed maximum removal efficiency (>98%) for optimal parameters. The experimental equilibrium data fitted reasonably well to Langmuir isotherm model. ANOVA analysis along with Fisher's statistical test was also performed to validate the model. The predicted model was at par with the experimental values with adjusted R² of 0.9914. A thorough investigation of kinetic ($R_{\text{Pseudo second order}}^2$ = 0.99; $R_{\text{Pseudo second order}}^2=0.97;R_{\text{intra}?\text{particle diffusion}}^2=0.98)$, thermodynamic, adsorption isotherm $(R_{\text{Langmuir isotherm}}^2=0.997$ $R_{\text{Freundlich isotherm}}^2=0.99$ and eco-toxicological characteristics were performed for proper evaluations of the properties as well as sustainability of the adsorbent material. The whole research indicated encouraging potential of the developed material for adsorption, reusability and sustainability in applications for industrial scale wastewater treatment.     

Normal- and Reversed-Phase Thin-Layer Chromatography of Amino Acids on Unconventional Supports with Mixed Mobile Phases Containing Dimethyl Sulfoxide

JPC – Journal of Planar Chromatography – Modern TLC - The chromatographic behavior of twenty-four amino acids has been studied on untreated and on triaryl phosphate (TAP)-impregnated...     

Synthesis, spectroscopy and cyclic voltammetry of new iron(III) complexes with 5-methyl-3-formyl pyrazole 3-hexamethyleneiminyl thiosemicarbazone (HMPz3Hex): X-ray crystallographic identification of [Fe(MPz3Hex)2]ClO4 · 2H2O with an indication for unusual rotation about the azomethine double bond on complexation with iron(III)

New iron(III) complexes of 5-methyl-3-formylpyrazole 3-hexamethyleneiminylthiosemicarbazone (HMPz3Hex), [Fe(MPz3Hex)₂]X · nH₂O (where X = Cl, NO₃or ClO₄ and n = 1–2) have been synthesized and physico-chemically characterized by magnetic data (polycrystalline state), electronic, i.r. and e.p.r. spectral studies. The reported complexes are all cationic electrolytes (1:1) containing two moles of monodeprotonated title ligand and an anionic counterpart. I.r. spectra (4000–200 cm^?1) indicate coordination to the central iron(III) ion via the pyrazolyl (tertiary) ring nitrogen, azomethine nitrogen and thiolato sulphur atoms of the primary ligand molecule. E.p.r. data (r.t. and l.n.t.) show the presence of a low-spin iron(III) cation with d _xz ² d _xz ² d _xz ¹ configuration. Cyclic voltammograms of iron(III) complexes indicate a reversible Fe⁺³/Fe⁺² couple. X-ray data of [Fe(MPz3Hex)₂]ClO₄ · 2H₂O (P₁, triclinic) authenticate a FeN₄S₂ distorted octahedral coordination with the two azomethine nitrogens trans to each other; the pyrazolyl nitrogens and thiolato sulphurs are in cis-positions, indicating an unusual rotation about the azomethine (C=N) double bond of the free HMPz3Hex during complexation with iron(III).     

Influence of unsaturated aliphatic and aromatic volatile organic compounds on the oxidation of aqueous sulfur dioxide by oxygen in aqueous medium

The trace atmospheric volatile organic compounds(VOCs) are reported to influence the oxidation of dissolved sulfur dioxide, S(IV), by oxygen, which is an important reaction in atmospheric acid formation. In this work, the influence of 15 VOCs on uncatalyzed oxidation of S(IV) by oxygen has been investigated by following the disappearance of [O₂]. The inhibition of oxidation reaction by toluene, aniline, benzene, cinnamic acid, hydroquinone, acrylamide, acrylonitrile and allyl alcohol was defined by the rate law(A):k_VOC = k₀/(1+B [Inh]) (A)where, k_VOC, and k₀ are the first order rate constants in the presence and the absence of VOCs respectively. B is the inhibition parameter and [Inh] is the concentration of inhibitor.On the other hand, fumaric, maleic and crotonic acids, which have conjugated CC bonds, catalyze the reaction defined by the rate law(B):k_VOC = k₀ + k_cat [VOC] (B)where k_cat is catalytic constant and [VOC] is the concentration of catalytic VOC.Interestingly, presence of 1-hexene, cyclohexene, methacrylic acid, methyl acrylate was without any significant effect on the rate of reaction.     

Dynamics of polar solvation: Route to single exponential relaxation via translational diffusion

A microscopic theoretical calculation of time-dependent solvation energy shows that the solvation of an ion or a dipole is dominated by a single relaxation time if the translational contribution to relaxation is significant. Contribution No. 545 from the Solid State and Structural Chemistry Unit