Some limiting factors of the ion-exchange equilibrium method for determining apparent formation constants of mononuclear complexes

Some limiting analytical conditions of the ion-exchange equilibrium method are discussed. The most reliable apparent formation constants are obtained when the range of the experimental complexant concentration brackets the reciprocal value of the stability constant for ML-type complexes. This working range will ensure significant analytical differences in the total metal remaining in solution for successive experiments with increasing complexant concentrations. For accurate determination of stepwise formation constants for ML(2)-type complexes, the intermediate complex species ML(+) must not be exchanged by the resin to any extent. Otherwise Schubert's equations are no longer valid, and the partition ratios of all cationic species present should be taken into account.     

Effect of the complexant shape on the large first hyperpolarizability of alkalides Li+(NH3)4M-.

The effect of complexant shape effect on the first hyperpolarizability beta(0) of alkalides Li(+)(NH(3))(4)M(-) (M=Li, Na, K) was explored. At the MP2/6-311++G level, Li(+)(NH(3))(4)M(-) (M=Li, Na, K) have considerable beta(0) values due to excess electrons from chemical doping and charge transfer. By comparison with the alkalides Li(+)(calix[4]pyrrole)M(-), a complexant shape effect in Li(+)(NH(3))(4)M(-) is detected. The beta(0) values of Li(+)(NH(3))(4)M(-) with the "smaller", inorganic, T(d)-symmetric (NH(3))(4) complexant are more than four times larger than those of Li(+)(calix[4]pyrrole)M(-) with the "larger", organic C(4v)-symmetric calix[4]pyrrole complexant. The ratios of the beta(0) values of Li(+)(NH(3))(4)M(-) and Li(+)(calix[4]pyrrole)M(-) are 6.57 (M=Li ), 6.55 (M=Na), and 5.17 (M=K). In the Li(+)(NH(3))(4)M(-) systems, the NBO charge and oscillator strength are found to monotonically depend on the atomic number of the alkali metal anion. The order of the NBO charges of the alkali anions M(-) is -0.667 (M=Li )>-0.644 (M=Na)>-0.514 (M=K), while the order of the oscillator strengths in the crucial transition is 0.351 (M=Li )<0.360 (M=Na)<0.467 (M=K). This indicates that complexant shape effects are strong, and consequently the beta(0) values of Li(+)(NH(3))(4)M(-) are found to be beta(0)=70 295 (M=Li )<96 780 (M=Na)<185 805 a.u. (M=K). This work reveals that the use of a high-symmetry complexant is an important factor that should be taken into account when enhancing the first hyperpolarizability of alkalides by chemical doping.     

Thermometric titrations at elevated temperatures

The oxidizing power of hexacyanoferrate(III) in alkaline conditions is wellknown. Unfortunately many if its oxidation reactions are too slow at room temperatures for direct titrimetric procedures. A method has been developed for the determination of millimolar amounts of selenium(IV), arsenic(III), antimony(III), chromium(III), and thallium(I) using thermometric titrimetry at approximately 330 K. The reproducibility and accuracy of the method are approximately 1%.     

Complexation of N4-Tetradentate Ligands with Nd(III) and Am(III)

To improve understanding of aza-complexants in trivalent actinide?Clanthanide separations, a series of tetradentate N-donor ligands have been synthesized and their complexation of americium(III) and neodymium(III) investigated by UV?Cvisible spectrophotometry in methanolic solutions. The six pyridine/alkyl amine/imine ligands are N,N??-bis(2-methylpyridyl)-1,2-diaminoethane, N,N??-bis(2-methylpyridyl)-1,3-diaminopropane, trans-N,N-bis(2-pyridylmethyl)-1,2-diaminocyclohexane (BPMDAC), N,N??-bis(2-pyridylmethyl)piperazine, N,N??-bis-[pyridin-2-ylmethylene]ethane-1,2-diamine, and trans-N,N-bis-([pyridin-2-ylmethylene]-cyclohexane-1,2-diamine. Each ligand has two pyridine groups and two aliphatic amine/imine N-donor atoms arranged with different degrees of preorganization and structural backbone rigidity. Conditional stability constants for the complexes of Am(III) and Nd(III) by these ligands establish the selectivity patterns. The overall selectivity of Am(III) over Nd(III) is similar to that reported for the terdentate bis(dialkyltriazinyl)pyridine molecules. The cyclohexane amine derivative (BPMDAC) is the strongest complexant and shows the highest selectivity for Am(III) over Nd(III) while the imines appear to prefer a bridging arrangement between two cations. These results suggest that this series of ligands could be employed to develop an enhanced actinide(III)?Clanthanide(III) separation system.     

Titanocene(III)-promoted Reformatsky additions

[reaction: see text] A novel method for the promotion of Reformatsky-like reactions is presented. The technique employs titanocene(III) chloride as a mild and homogeneous single-electron reductant. The reactions are rapid, operationally simple, and compatible with a wide range of functionalities. These additions are also anti diastereoselective.     

Kinetic spectrophotometric method for o-phenylenediamine in the presence of gold(III)

From the color developing reactions of o-phenylenediamine oxidizing agent and gold(III), the kinetic reactions between both of them in aquaeous solutions were studied using spectrophotometric and differential method. Light absorbances in the visible spectral range are measured as a function of mole fractions of phenylenediamine at a fixed gold(III) concentration and as a function of mole fraction of gold(III) at a fixed o-phenylenediamine concentration at periodic time internal. In the differential method, which was suggested by van't Hoff, one deals with the actual rates of reactions as determined by measuring the slopes of absorbance-time curves. Optimum condition of the reaction were established as pH 6 at lambda=466 nm and room temperature. When the oxidation of o-phenylenediamine by gold(III) was investigated, it was observed that the following rate formula and rate constant were found: v=k[Au+3]1/2[o-phenylenediamine]1/2, k=2.33x10(-2) s-1.     

Alkali metals plus complexants: From alkalides and electrides to aromatic anions

Electron transfer from an alkali metal to a suitable complexant for the cation can yield crystalline ionic solids that contain the complexed cation and either an alkali metal anion (alkalide) or a trapped electron (electride). The nature and properties of electrides are emphasized in this paper. When the organic complexant contains aromatic groups, the anionic species is an aromatic radical anion. Preliminary work on the addition of alkali metals to LOGEAs (large organic globular electron acceptors) is described and strategies for the synthesis of mixed electride-anion compounds are considered.     

固相配位化学反应研究——ⅩⅩⅩⅩⅠ.[Co(NH_3)_5(H_2O)]Br_3,[Cr(NH_3)_5(H_2O)](NO_3)_3与无机盐KY(Y=Cl,Br,Ⅰ)的固相反应动力学研究

本文主要用气相色谱逸出气体分析方法,借助于红外、紫外可见漫反射谱等手段研究了[Co(NH_3)_5(H_2O)]Br_3、[Cr(NH_3)_5(H_2O)](NO_3)_3与无机盐KY(Y=Cl,Br,Ⅰ)的固相反应,计算了失水与失氨的动力学参数,发现第一步反应失水生成一取代中间产物,其活化能与外加阴离子无关,为S_N1过程。第二步失氨反应活化能与中心离子M以及取代基Y有关,当M=Co(Ⅲ)时,反应体系的失氨活化能大小有下列顺序:Cl>Br>Ⅰ(E值分别为187、155、98kJ·mol~(-1)),M=Cr(Ⅲ)时则正好相反:Ⅰ>Br>Cl(E值分别为213、146、79 kJ·mol~(-1))。     

高效毛细管电泳法测定镍盐中的钴含量

用２－亚硝基－１－萘酚－５－磺酸与Ｎｉ、Ｃｏ络合,在波长５３０ｎｍ和其他优化测定条件下,用高效毛细管电泳法定量测定市售镍盐中微量钴,为测定镍 微量钴提供了一种快速,简便的新方法。     

STABILITIES OF IRON(III) COMPLEXES WITH 3- AND 4-HYDROXYPYRIDINE

Abstract

Equilibrium constants for the reaction of 3- or 4-hydroxypyridine with iron(III) were measured in aqueous solution. The experimental method involved the measurement of hydrogen ion concentration and optical absorbance for each of a series of reaction mixtures. The results are consistent with the interpretation that the separate interactions between iron(III) and the hydroxypyridines are of the hard acid-hard base type, with sigma bonding alone being important. Equilibrium constants are reported for both the reactions in which iron(III) displaces a proton in protonated hydroxypyridine and for the direct combination of iron(III) and the hydroxypyridine.     

Determination of the valence distribution of vanadium in polyolefin catalysts prepared from vanadium trichloride

An electrochemical method has been developed for determining the relative amounts of V(II) and V(III) in polyolefin catalysts prepared using aluminum alkyls and vanadium trichloride. The catalyst, usually obtained as a slurry in n-heptane, is titrated potentiometrically with ceric sulfate using a platinum indicator electrode. Under proper experimental conditions, 2 breaks are obtained, corresponding to the reactions V(II) →V(III) + e and V(III) →V(IV) + e. Interferences from other components of the catalyst are negligible. The method is useful for the analysis of both laboratory catalysts and grab samples taken from pilot plant reactors.     

Complexation of Am(III) and Nd(III) by 1,10-Phenanthroline-2,9-Dicarboxylic Acid

The complexant 1,10-phenanthroline-2,9-dicarboxylic acid (PDA) is a planar tetradentate ligand that is more preorganized for metal complexation than its unconstrained analogue ethylendiiminodiacetic acid (EDDA). Furthermore, the backbone nitrogen atoms of PDA are aromatic, hence are softer than the aliphatic amines of EDDA. It has been hypothesized that PDA will selectively bond to trivalent actinides over lanthanides. In this report, the results of spectrophotometric studies of the complexation of Nd(III) and Am(III) by PDA are reported. Because the complexes are moderately stable, it was necessary to conduct these titrations using competitive equilibrium methods, competitive cation complexing between PDA and diethylenetriaminepentaacetic acid, and competition between ligand protonation and complex formation. Stability constants and ligand protonation constants were determined at 0.1 mol·L^?1 ionic strength and at 0.5 mol·L^?1 ionic strength nitrate media at 21 ± 1 °C. The stability constants are lower than those predicted from first principles and speciation calculations indicate that Am³⁺ selectivity over Nd³⁺ is less than that exhibited by 1,10-phenanthroline.     

Kinetics and mechanism of indigo carmine-acidic iodate reaction. An indicator reaction for catalytic determination of Ru(III) ion

A kinetic study of uncatalyzed and Ru(III) catalyzed oxidation of indigo carmine(IC) (disodium 3,3′-dioxobi-indolin-2,2′-ylidene-5,5′-disulphonate) by iodate ion in aqueous sulphuric acid solution is reported. The uncatalyzed reaction order was found to be four; one each with respect to IC and iodate ion and second order with H⁺ ion. The Ru(III) catalyzed reaction was of fifth order, second order with respect to H⁺ and first order with respect to reductant, oxidant, and catalyst. Stoichiometric ratios of both reactions were the same with a 3:2 reductant-oxidant ratio. In both uncatalyzed and catalyzed reactions isatin-5-monosulphonic acid (2,3-dioxoindoline-5-sulphonic acid) was observed as the oxidation product. Rate constants for both the reactions are reported. Reaction mechanisms consistent with the experimental data are suggested. Further, a fixed time method is described for the determination of Ru(III), based on its ability to catalyze the oxidation of IC by acidic iodate. Using [H⁺] 2.25M, [iodate] 1.00 × 10^?3M and [IC] 5.0 × 10^?5M, in presence of Ru(III), the reaction followed first order kinetics with respect to IC. The interference of various cations, neutral salts, and potassium iodide on the determination of Ru(III) was studied using synthetic mixtures. The selectivity of the method and the recommended procedure are described.     

Micellar catalysis in reactions of some β-lactam antibiotics with p -dimethylaminobenzaldehyde

Kinetic study of the reactions of amoxicillin (I), ampicillin (II) and cephlaxin (III) with p-dimethylaminobenzaldehyde (DAB) in weakly acidic EtOH/H₂O solution has been investigated using spectrophotometric method. Relatively slow reversible reactions of first order with respect to the antibiotic have been found. A derived equation for detecting the existence of reversibility from the linearity has been introduced. The effect of anionic surfactants (sodium dodecyl sulfate, SDS) on the kinetic of these reactions in aqueous solution has been studied. The presence of 0.005 M of SDS increases the rate constants by 4.3, 2 and 3.3 times for I, II and III, respectively. The consequence of the rate constants have a similar order in absence and presence of SDS; III > II > I. The rate constants pass through maxima with increasing SDS concentration followed by a gradual but steady decrease in the rate as the surfactant concentration increases further. Multiple linear regression method has been performed to evaluate the binding constants of each drug and DAB with SDS from the resulted kinetic data. The results suggest using multiple linear correlation method for such calculations, which is more accurate, reliable and less time consuming. The calculated binding constants between these drugs with SDS are following the consequence I > II > III which is related to the differences in their substitutions. The kinetic results were employed for spectrophotometric microdetermination of these drugs (I–III) in aqueous solution. The method was based on the reaction of β-lactam with an excess of DAB in presence of SDS and HCl (pH 2) at a wavelength 410 nm. The results indicate that the presented method is simple, precise and accurate. This method is applied to bulk antibiotics and some of their pharmaceutical preparations.     

Simultaneous determination of speciation parameters of Cu,Pb, Cd and Zn in model solutions of Suwannee River fulvic acid by pseudopolarography

There is a growing awareness of the importance of quantitative determinations of speciation parameters of the trace metals Cu, Zn, Cd and Pb in aqueous samples containing chemically heterogeneous humic substances, especially when they are present together, interacting with one another and competing for specific binding sites of the humic substances. Such determinations require fundamental knowledge and understanding of these complex interactions, gained through basic laboratory-based studies of well-characterized humic substances in model solutions. Since the chemical heterogeneity of humic substances plays an important role in the thermodynamics (stability) and kinetics (lability) of trace metal competition for humic substances, a metal speciation technique such as pseudopolarography that can reveal the special, distinctive nature of metal complexation is required, and it was therefore used in this study. A comparison of the heterogeneity parameters (Gamma) for Zn(II), Cd(II), Pb(II) and Cu(II) complexes in model solutions of Suwannee River fulvic acid (SRFA) shows that GammaCd>GammaZn>GammaPb>GammaCu, suggesting that SRFA behaves as a relatively homogeneous complexant for Zn(II) and Cd(II), whereas it behaves as a relatively heterogeneous complexant for Pb(II) and an even more heterogeneous complexant for Cu(II) under the experimental conditions used. The order of values of log K* (from the differential equilibrium function, DEF) for the trace metals at pH 5.0 follow the sequence: log K*Cu>log K*Pb>log K*Zn>log K*Cd. These results are in good agreement with the literature values. The results of this work suggest the possibility of simultaneously determining several metals in a sample in a single experiment, and hence in a shorter time than required for multiple experiments.     

Hydrogenation of molecular cyclic diborane4 compounds featuring B-B bonds and olefinic or aromatic bridges: a quantum chemical study

Hydrogenation reactions starting with di- or oligonuclear boron compounds featuring direct B-B bonds with the B atoms in the formal oxidation state +II are analyzed with the aid of ab initio quantum chemical (RI-MP2) calculations. The products of these reactions are B(III) hydrides which might be useful starting reagents for stoichiometric hydrogenation reactions and possibly in special cases also for hydrogen storage. Several different isomers of these B(III) hydrides featuring either terminal or bridging H atoms were considered. The results are compared to hydrogenation reactions of related molecules.     

Study on Chemiluminescence Reactions of Lucigenin and Reductants by Flow Injection Analysis

Preceding studies involved two kinds of chemiluminescence (CL) reactions of Lucigenin(Lu ),one was the reaction of Lu with H=O, catalyzed by metal ions, the other was that ofLu with organic reductants such as glucose, uric acid and so on.We found that Mo (Ill),V (11 ),U (ill),W (ill),Cr (11 ),Ti (ill) and Fe (11 ), whichwere produced on-line by passing Mo (VI),V (V ),U (VI), W (VI), Cr (VI,lll),Ti (N) andFe (ill) through a micro Jones column', can react with Lu to generate strong …     

Separation and micro-identification of metallic ions by ring oven technique. I

Summary Attempts to separate Hg(I), Pb(II), Ag(I), Hg(II), Bi(III), Cu(II), Cd(II), As(III), Sb(III) and Sn(II) in ternary, quaternary and quinary mixtures by the Weisz ring oven technique have been made, using oxalate as complexing agent and aqueous ethanol as solvent. It is found, in general, that addition of oxalate as complexing agent enables separations to be carried out which do not occur in the uncomplexed solutions. The effect of adding varying concentrations of the complexing agent to the solutions has been studied. The sequences of separation in ternary, quaternary and quinary mixtures with varying concentrations of the complexing agent have been described.

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Zusammenfassung Es wurde versucht, Hg(I), Pb(II), Ag(I), Hg(II), Bi(III), Cu(II), As(III), Sb(III) und Sn(II) in Drei-, Vier- und Fünfstoffgemischen unter Verwendung von Oxalat als Komplexbildner und wäßrigem Äthanol als Lösungsmittel nach der Ringofentechnik vonWeisz zu trennen. Im allgemeinen ermöglicht die Komplexierung mit Oxalat Trennungen, die sonst nicht durchführbar sind. Die Einwirkung verschiedener Konzentrationen des Komplexbildners auf die Probelösungen wurde geprüft. Die Reihenfolge der Trennung aus den angeführten Mischungen bei verschiedener Oxalatkonzentration wird angegeben.

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Résumé On a essayé de réaliser la séparation de Hg-I, Pb-II, Ag-I, Hg-II, Bi-III, Cu-II, Cd-II, As-III, Sb-III et Sn-II dans des mélanges ternaires, quaternaires et quinquénaires, au moyen de la technique du four annulaire deWeisz, en utilisant des oxalates comme agents complexants et l'éthanol aqueux comme solvant. On a trouvé que, généralement, l'addition d'oxalates comme agents complexants oblige à effectuer des séparations qui ne se rencontrent pas dans les solutions non complexées. On a étudié l'effet de l'addition de concentrations variables de l'agent complexant aux solutions. On a décrit les étapes de la séparation dans les mélanges ternaires, quaternaires et quinquénaires pour des concentrations variables de l'agent complexant.

     

Catalytic determination of nanogram amounts from iron(III) using its catalytic effect on the oxidation of sodium pyrogallol-5-sulphonate by hydrogen peroxide

A kinetic method is described for the determination of iron(III) based on its catalytic effect on the oxidation of sodium pyrogallol-5-sulphonate by hydrogen peroxide. The reaction was followed spectrophotometrically by measuring the rate of change in the absorbance of the coloured product at 436.8 nm. Nanogram amounts of iron(III) (2.0-75.0 ng cm(-3)) can be determined with good accuracy and reproducibility. The influence of foreign ions on the results was investigated and the method was found to be adequately selective. It has been applied satisfactorily to the determination of iron(III) in tap water samples. The kinetic parameters of both the catalysed and uncatalysed reactions are reported.     

The coordination chemistry of simple phospholes. Complexes of rhenium,ruthenium, cobalt,rhodium and iridium chlorides and of some chlorocarbonyls of ruthenium and rhodium

The reactions of 1-phenylphosphole (PP), 3-methyl-1-phenylphosphole (mPP), 3,4-dimethyl-1-phenylphosphole (dPP) and, in certain instances, 1-n-butyl-3,4-dimethylphosphole (dBP) with some transition metal chlorides and some metal-Cl-CO systems are reported. These reactions show that simple phospholes in general unexpectedly behave much like ordinary tertiary phosphines and that, unlike the reactions with Ni(II), Pd(II) and Pt(II), the complexes formed are conventional in most respects. However, a few unusual reactions were observed. For example, mPP partially reduces Ru(III) to give a mixed-valent Ru(III)-Ru(II) complex while PP reduces Ir(III) to Ir(I). From infrared spectroscopic studies of the square-planar Rh(I) complexes L₂Rh(CO) Cl (L = phosphole), it appears that donor character decreases with decreasing substitution on the phosphole ring carbon atoms. Phosphorus-phenyl cleavage has been observed in reactions of 1-phenylphosphole with Rh-CO systems. The results are briefly discussed in relation to the behaviour of other phospholes in similar reactions and in the context of the electronic structure of phospholes.