Studies on Mn(II) and Mn(IV) Complexes of an Unsymmetrical Bidentate Donor,N(4-Chlorophenyl)-Pyridine-2-Aldimine (ClL): Crystal Structure of [Mn(ClL)2(NCS)2]

The synthesis, characterisation and X-ray structure of an Mn(II) compound, [Mn(ClL)₂(NCS)₂], is described. Oxidation of the compound by H₂O₂ leads to a mononuclear Mn(IV) compound [Mn(ClL)(ClL')(NCS)₂]ClO₄·2H₂O where one of the ClL ligands is oxidised to the corresponding amide ClL'. Oxidation of [Mn(ClL)₂(NCS)₂] by Ce(IV), however, leads to a binuclear Mn(IV) compound [Mn₂O(ClL')₃(ClL)(H₂O)₂](NCS)₂ClO₄·2MeCN. Electron transfer behaviour of the compounds was investigated by cyclic voltammetry and differential pulse voltammetry.     

Rapid and selective determination of osmium(IV) by UV-visible spectrophotometry using o-methylphenyl thiourea as a chromogenic chelating ligand: sequential separation of osmium(IV), rhodium(III) and platinum(IV)

The objective of this research work was to develop a simple, highly sensitive and precise method for spectrophotometric determination of osmium(IV). O-Methylphenyl thiourea (OMPT) coordinates with osmium(IV) as a 1:1 (osmium(IV)–OMPT) complex in hydrochloric acid media (0.8 mol l^?1). The novelty of the investigated method is instant complex formation at room temperature with no need of heating or standing. The complex is stable for more than 8 days. The method is applicable over a wide linearity range (up to 110 µg ml^?1). A low reagent concentration is required (2 ml, 0.009 mol l^?1 in ethanol). The complex exhibits maximum absorption in the range of wavelength 510–522 nm and 514 nm was selected for further study. The molar absorptivity was 1.864 × 10³ l mol^?1 cm^?1, Sandell’s sensitivity was 0.102 µg of osmium(IV) cm^?2. Proposed method was successfully applied for separation and determination of osmium(IV) from binary and ternary synthetic mixtures containing associated metal ions. A scheme for mutual separation of osmium(IV), rhodium(III) and platinum(IV) is developed.     

Bromo-substituted Mn(II) and Mn(III)-tetraarylporphyrins: synthesis and properties

Abstract

Mono-, tetra-, and octa-bromo substituted Mn(II)- and Mn(III)-tetraarylporphyrins were synthesized by reactions of manganese(II) chloride with corresponding porphyrin ligands or their Cd(II)-complexes in DMF. With the use of the metal exchange reaction, the time of the Mn-porphyrins formation is significantly reduced with increase in yield of final products in comparison with the complexation reaction. Mn(III)-tetraarylporphyrins reduce to the Mn(II)-porphyrins in DMF in the presence of NaOH and in pure DMF. The obtained compounds were identified using UV–vis and ¹H NMR spectroscopy, mass-spectrometry, and elemental analysis.     

Tropoloae as a specific reagent for the determination of vanadium(V)

The blue colour developed on interaction of vanadium(V) with tropolone m 5.5-7.0N acid can be extracted into chloroform. The complex has an absorption maximum at 590 nm. Colour development is instantaneous and the extracted species is stable for 72 hr. Beer's law is followed in the range 1.02-14.25 ppm of vanadium. The molar absorptivity is 4.63 x 10(3)l.mole(-1).cm(-1). Most anions do not interfere. Of the 37 cations examined, only Ti(III), Ru(III), Pt(IV), Ir(IV), Mn(II), Ta(V) and Ce(III) were found to interfere. The interference due to these cations has been removed by masking them with EDTA.     

Oxidation Of Di-Peptides With Mn(III): Synthesis, Characterization And Mechanistic Study

Synthesis and characterization of the dipeptides(DP) namely Glycyl-Proline (Gly-Pro), Alanyl-Proline (Ala-Pro) and Valyl-Proline (Val-Pro), were made. Kinetics of oxidation of these DP by Mn(III) have been studied in the presence of sulfate ions in acidic medium at 26C. The reaction was followed spectrophotometrically at _max = 500 nm. A first order dependence of rate on both Mn(III) and DP was observed. The rate is independent of the concentration of reduction product, Mn(II) and hydrogen ions. Effects of varying dielectric constant of the medium and addition of anions such as sulfate, chloride and perchlorate were studied. Activation parameters have been evaluated using Arrhenius and Eyring plots. The oxidation products were isolated and characterized. A mechanism involving the reaction of DP with Mn(III) in the rate limiting step is suggested.     

Preparation,Spectroscopic Properties and Characterization of Oxovanadium(IV), Isothiocyanatomanganese(III), Cyanocobalt(III) and Cobalt(II) Complexes with a Bis-Crown Ether Tetraaza[14]Annulene

Oxovanadium(IV), isothiocyanatomanganese(III), cyanocobalt(III) and cobalt(II) complexes of tetraaza[14]annulene appended with two crown ethers at 2,3- and 11,12-positions have been prepared. Cation complexation behavior of these cavity-bearing tetraaza[14]annulene complexes has been investigated by optical absorption methods. The cation K + , which necessitates two crown ether cavities for complexation, induces dimerization of the tetraaza[14]annulene complexes, whereas the Na + does not. Formation of the sandwich complexes due to dimerization is hindered by the steric interactions involving the axial ligand as judged by the blue shift of the intense band around 385-425 nm. Judging from its ESR spectrum, the cobalt(II) complex becomes a monomeric dioxygen complex of a 1 : 1 molar ratio in the presence of O 2 and pyridine at 77 K.     

Kinetic Study of the Ce(III)‐, Mn(II)‐, or Ferroin‐Catalyzed Belousov‐Zhabotinsky Reaction with Allylmalonic Acid

In a stirred batch experiment and under aerobic conditions, ferroin (Fe(phen)₃²⁺) behaves differently from Ce(III) or Mn(II) ion as a catalyst for the Belousov‐Zhabotinsky (BZ) reaction with allylmalonic acid (AMA). The effects of bromate ion, AMA, metal‐ion catalyst, and sulfuric acid on the oscillating pattern were investigated. The kinetics of the reaction of AMA with Ce(IV), Mn(III), or Fe(phen)₃³⁺ ion was studied under aerobic or anaerobic conditions. The order of reactivity of metal ions toward reaction with AMA is Fe(phen)₃³⁺ > Mn(III) > Ce(IV) under aerobic conditions whereas it is Mn(III) > Ce(IV) > Fe(phen)₃³⁺ under anaerobic conditions. Under aerobic or anaerobic conditions, the order of reactivity of RCH(CO₂H)₂ (R = H (MA), Me (MeMA), Et (EtMA), allyl (AMA), n‐Bu (BuMA), Ph (PhMA), and Br (BrMA)) is PhMA > MA > BrMA > AMA > MeMA > EtMA > BuMA toward reaction with Ce(IV) ion and it is MA > PhMA > BrMA > MeMA > AMA > EtMA > BuMA toward reaction with Mn(III) ion. Under aerobic conditions, the order of reactivity of RCH(CO₂H)₂ toward reaction with Fe(phen)₃³⁺ ion is PhMA > BrMA > (MeMA, AMA) > (BuMA, EtMA) > MA. The experiment results are rationalized.     

铂电极上醋酸-醋酐溶液中Mn(III)/Mn(II)电对研究

平衡电极电势实验确定了25 ℃, 1.5 mol•L－1醋酸钾＋醋酸-醋酐(3:1体积比)溶液中Mn(III)/Mn(II)的条件电极电势为0.719 V（vs SCE）;采用电势扫描和旋转圆盘电极技术研究了醋酸-醋酐溶液中铂电极上Mn(III)/Mn(II)电对的阳极氧化动力学. 结果表明:Mn(II)阳极氧化成Mn(III)的电极反应控制步骤属电荷传递过程, 阳极传递系数β=0.347,交换电流密度i0=5.84×10－6 A•cm－2,阳极标准反应速率常数ka=1.35×10－8 m•s－1, Mn(II)和OAc－的反应级数均为一级.     

Triazine based Mn (II) and Mn (II)/Ln (III) complexes: Synthesis,characterization and catecholase activities

In the current work, two triazine‐based multidentate ligands (H₂L¹ and H₂L²) and their homo‐dinuclear Mn (II), mononuclear Ln (III) and hetero‐dinuclear Mn (II)/Ln (III) (Where Ln: Eu or La) complexes were synthesized and characterized by spectroscopic and analytical methods. Single crystals of a homo‐dinuclear Mn (II) complex {[Mn (HL¹)(CH₃OH)](ClO₄·CH₃OH}₂ ( 1 ) were obtained and the molecular structure was determined by X‐ray diffraction method. In the structure of the complex, each Mn (II) ion is seven‐coordinate and one of the phenolic oxygen bridges two Mn (II) centre forming a dimeric structure. The UV–Vis. and photoluminescence properties of synthesized ligands and their metal complexes were investigated in DMF solution and the compounds showed emission bands in the UV–Vis. region. The catecholase enzyme‐like activity of the complexes were studied for 3,5‐DTBC → 3,5‐DTBQ conversion in the presence of air oxygen. Homo‐dinuclear Mn (II) complexes ( 1 and 4 ) were found to efficiently catalyse 3,5‐DTBC → 3,5‐DTBQ conversion with the turnover numbers of 37.25 and 35.78 h^?1 (k_cat), respectively. Mononuclear Eu (III) and La (III) complexes did not show catecholase activity.     

Synthesis and structural characterization of manganese(III,IV) and ruthenium(III) complexes derived from 2-hydroxy-1-naphthaldehydebenzoylhydrazone

Reaction of 2-hydroxy-1-naphthaldehydebenzoylhydrazone(napbhH₂) with manganese(II) acetate tetrahydrate and manganese(III) acetate dihydrate in methanol followed by addition of methanolic KOH in molar ratio (2 : 1 : 10) results in [Mn(IV)(napbh)₂] and [Mn(III)(napbh)(OH)(H₂O)], respectively. Activated ruthenium(III) chloride reacts with napbhH₂ in methanolic medium yielding [Ru(III)(napbhH)Cl(H₂O)]Cl. Replacement of aquo ligand by heterocyclic nitrogen donor in this complex has been observed when the reaction is carried out in presence of pyridine(py), 3-picoline(3-pic) or 4-picoline(4-pic). The molar conductance values in DMF (N,N-dimethyl formamide) of these complexes suggest non-electrolytic and 1 : 1 electrolytic nature for manganese and ruthenium complexes, respectively. Magnetic moment values of manganese complexes suggest Mn(III) and Mn(IV), however, ruthenium complexes are paramagnetic with one unpaired electron suggesting Ru(III). Electronic spectral studies suggest six coordinate metal ions in these complexes. IR spectra reveal that napbhH₂ coordinates in enol-form and keto-form to manganese and ruthenium metal ions in its complexes, respectively. ESR studies of the complexes are also reported.     

An Efficient Aerobic Oxidation for p-Xylene to p-Toluic Acid using Azacrown Ether-tethered Mn(III) Schiff Base Complexes as Catalysts

The oxidation of p-xylene to p-toluic acid with air at 110°C under normal atmospheric pressure occurs efficiently in the presence of crown Mn(III) Schiff base complexes [Formula: See Text] (n=1-4). Significant conversion levels (up to 75%) and selectivity (up to 92-96%) are obtained; the effect of the azacrown ether pendants in Mn(III) Schiff base complexes on the oxidation of p-xylene are also investigated by comparison with the crown-free analogues [Formula: See Text] Moreover, addition of alkali metal ions accelerates the rate of conversion of p-xylene to p-toluic acid.     

A family of hexanuclear Mn(III) single-molecule magnets

In an attempt to employ salicylic acid (HOsalH), 2,6-dihydroxy benzoic acid {(HO)₂PhCO₂H}, and naphthalene-1,8-dicarboxylic acid {1,8-naph(CO₂H)₂} in Mn(III) salicylaldoximate chemistry as a means to alter the structural identity of the hexanucluear clusters usually obtained from this reaction system, we have isolated a family of hexanuclear Mn(III) complexes based on salicyladloxime (saoH₂) and 2-hydroxy-1-naphthaldehyde oxime (naphthsaoH₂). Five hexanuclear clusters, [Mn₆O₂(sao)₆(HOsal)₂(EtOH)₄]·EtOH (1·EtOH), [Mn₆O₂(sao)₆{1,8-naph(CO₂Me)(CO₂)}₂(MeOH)₆]·3MeOH (2·3MeOH), [Mn₆O₂(naphthsao)₆{1,8-naph(CO₂Et)(CO₂)}₂(EtOH)₆] (3·2MeOH), [Mn₆O₂(naphthsao)₆(MeCO₂)₂(EtOH)₄]·2H₂O (4·2H₂O), and [Mn₆O₂(naphthsao)₆{(HO)₂PhCO₂}₂(EtOH)₄]·4EtOH (5·4EtOH), have been synthesized and characterized by single-crystal X-ray crystallography. The magnetic properties of 3, 4, and 5 are discussed.     

Spectrophotometric determination of thorium in food using 2-(2,5-disulfonic-4-methoxyphenylazo)-7-(2-hydroxyl-5-carboxylphenylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic acid

A new highly sensitive and selective chromogenic reagent, 2-(2,5-disulfonic-4-methoxyphenylazo)-7-(2-hydroxyl-5-carboxylphenylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic acid (1), was synthesized and applied to the spectrophotometric determination of trace thorium. In 5 mL of a 6 M perchloric acid medium, which greatly increases the selectivity, thorium reacts with 1 to form a 1: 2 green complex, having a sensitive absorption peak at 670 nm. Under optimal conditions, Beer’s law is obeyed over the range from 0 to 0.8 μg/mL Th(IV) and the apparent molar absorptivity is 2.09 × 10⁵ L/mol cm. It is found that, uranium(VI), Ti(IV), heavy rare earths, and most of other common metal ions do not interfere. The method has been tested on the determination of thorium in food samples with satisfactory results. The text was submitted by the authors in English.     

Mandelazo I As A Reagent For Zr(IV) Determination

Abstract

A spectromeric study of the reaction of the Zr(IV) ions with Mandelazo I was carried out. Absorption spectra revealed that the maximum absorption of the zirconium compound appears at a wavelength (316 nm) different from the maxima of the reagent (253 and 390 nm). Beer-Lambert law is followed for zirconium concentrations of the order of 8.8x 10^?5 M (i.e. 8 μg Zr (IV)/mL). Possible interferences of ions such as Be(II), Cu(II), Zn(II), Al(III), Th(IV), U(VI), Mn(II), Fe(III), Co(II) and Ni(II) were investigated in connection with some masking agents such as SO₄ ^2- and C₂O₄ ^2-. Also, the solid state Zr(IV)-Mandelazo I compound was prepared and characterized by nitrogen and thermogravimetric analyses.     

Structural and physical characterization of tetranuclear [Mn(II)3Mn(IV)] and [Mn(II)2Mn(III)2] valence-isomer manganese complexes

Two tetranuclear Mn complexes with an average Mn oxidation state of +2.5 have been prepared. These valence isomers have been characterized by a combination of X-ray crystallography, X-ray absorption spectroscopy, and magnetic susceptibility. The Mn(II)3Mn(IV) tetramer has the Mn ions arranged in a distorted tetrahedron, with an S = 6 ground spin state, dominated by ferromagnetic exchange among the manganese ions. The Mn(II)2Mn(III)2 tetramer also has a distorted tetrahedral arrangement of Mn ions but shows magnetic behavior, suggesting that it is a single-molecule magnet. The X-ray absorption near-edge structure (XANES) spectra for the two complexes are similar, suggesting that, while Mn XANES has sufficient sensitivity to distinguish between trinuclear valence isomers (Alexiou et al. Inorg. Chem. 2003, 42, 2185), similar distinctions are difficult for tetranuclear complexes such as that found in the photosynthetic oxygen-evolving complex.     

Oxidative polymerization of acrylamide in the presence of thioglycolic acid

Chemical polymerization of acrylamide at room temperature was examined by using thioglycolic acid-cerium (IV) sulfate and thioglycolic acid-KMnO₄ redox systems in acid aqueous medium. Water soluble polyacrylamides containing thioglycolic acid end groups were synthesized. The effects of the molar ratio of acrylamide to Ce(IV) n _AAm /n _Ce(IV) , the polymerization time, the temperature, the monomer concentration, the molar ratio of cerium (IV) sulfate to thioglycolic acid and the concentration of sulfuric acid on the yield and molecular weight of polymer were investigated. Lower molar ratios of acrylamide/Ce(IV) at constant monomer concentration resulted in an increase in the yield but a decrease in molecular weight of polymer. The increase of reaction temperature from 20 to 70°C resulted in a decrease in the yield but generally resulted in a constant value for the molecular weight of polymer. With increasing polymerization time, the yield and molecular weight of polymer did not change substantially. Ce(IV) and Mn(VII) ions are reduced to Ce(III) and Mn(II) ions respectively in the polymerization reaction. The existence of Ce(III) ion bound to polymer was investigated by UV-visible spectrophotometry and fluoresce measurements. The amount of Mn(II) incorporated into the polymer was determined using graphite furnace atomic absorption spectrometry. The mechanism of this phenomenon is discussed.     

Simultaneous flow injection determination of iron(III) and vanadium(V) and of iron(III) and chromium(VI) based on redox reactions

A flow injection analysis (FIA) method is presented for the simultaneous determinations of iron(III)-vanadium(V) and of iron(III)-chromium(VI) using a single spectrophotometric detector. In the presence of 1,10-phenanthroline (phen), iron(III) is easily reduced by vanadium(IV) to iron(II), followed by the formation of a red iron(II)-phen complex (lambda(max) = 510 nm), which shows a positive FIA peak at 510 nm corresponding to the concentration of iron(III). On the other hand, in the presence of diphosphate the reductions of vanadium(V) and/or chromium(VI) with iron(II) occur easily because the presence of diphosphate causes an increase in the reducing power of iron(II). In this case iron(II) is consumed during the reaction and a negative FIA peak at 510 nm corresponding to the concentration of vanadium(V) and/or chromium(VI) is obtained. The proposed method makes it possible to obtain both positive (for iron(III)) and negative (for vanadium(V) or chromium(VI)) FIA peaks with a single injection.     

系列Mn(II)配位超分子的合成、晶体结构和表面光电压研究

采用水热合成方法得到了三种Mn(II)配位超分子: Mn(2,5-dcp)₂(H₂O)₂ (1), Mn(INA)₂(H₂O)₄ (2)和Mn(phen)₂Cl₂ (3) (2,5-dcp＝pyridine-2,5-dicarboxylic acid, INA＝iso-nicotinic acid, phen＝1,10-phenanthroline). 通过X射线单晶衍射、红外光谱(IR)、紫外光谱(UV-Vis)及表面光电压光谱(SPS)等方法对化合物进行了表征. 三种化合物中均存在大量的氢键, 使化合物晶体构成了无限延伸的三维网络结构. 表面光电压谱显示了化合物1～3在300～600 nm范围内呈现出正的光伏响应带, 具有P-型半导体的特征. 讨论了氢键在超分子构建中的作用以及不同配位环境对于配合物表面光电压的影响.     

Preparation of uranium(III) by mercury cathode electrolysis and its absorption spectra in hydrochloric acid solution

The reduction of hexavalent to trivalent uranium by mercury cathode electrolysis in hydrochloric acid solution was investigated. The dependence of the reducton ratio on the different media, the acid and uranium concentrations, and on the time of electrolysis was determined. It was found that hexavalent uranium can be reduced quantitatively to trivalent state by mercury cathode electrolysis. The absorption spectra of U(III) and U(IV) in 1M and 9M hydrochloric acid solutions were examined. The molar extinction coefficient of U(III) at 521 nm was 16.7 m²·mol^–1 within the HCl concentration range of 0.5–4.5M. U(IV) practically does not interfere in the photometric determination of U(III) at this wavelength. A good linear dependence of absorbance on the concentration of U(III) was found.     

丽春红S褪色光度法测定微量铈

依据在酸性条件下,铈Ce(IV)的强氧化性使丽春红S褪色的原理,建立了一种褪色光度法测定微量铈的新方法。实验结果表明:丽春红S溶液的最大吸收波长为510 nm,铈量在0～5.0 mg/L范围内遵循比尔定律,线性回归方程为:y=0.0048x-0.0068,相关系数为r=0.9993,表观摩尔吸光系数为ε510=2.18×104L.mol-1.cm-1。新方法用于稀土氧化物中微量铈的测定,样品分析结果的相对标准偏差为0.99%(n=5),加标回收率为96.9%～99.0%。