Kinetic and mechanistic studies on the interaction of<Emphasis Type="SmallCaps">DL</Emphasis> -Penicillamine with the hydroxopentaaquarhodium(III) ion

The kinetics of interaction between DL-Penicillamine and [Rh(H₂O)₅OH]²⁺ have been studied spectrophotometrically as a function of [Rh(H₂O)₅OH²⁺], [DL-Pen], pH and temperature. The reaction has been monitored at 242 nm, the _max of the substituted complex and where the spectral difference between the reactant and product is a maximum. The reaction rate increases with [DL-Pen] and reaches a limiting value at a higher ligand concentration. From the experimental findings an associative interchange mechanism for the substitution process is suggested. The activation parameters (H}=35.8 ± 1.6 kJ mol^–1, S=–209 ± 5 J K^–1 mol^–1) support the proposition. The negative G ⁰ (–13.6 kJ mol^–1) for the first equilibrium step also supports the spontaneous formation of an outersphere association complex.     

Nicotinamidoxime as an analytical reagent

Summary Uranium (VI) has been found to give a yellow colour with nicotinamidoxime in alkaline medium which is highly satisfactory for the spectrophotometric estimation of the metal. The optimumph for development of the colour is 10.9–11.5 in presence of a large excess of the reagent, at 10–40C. The colour intensity is measured at 400 m. Sensitivity is 0.045 g uranium per cm², with a visual identification limit of 5 g uranium per ml. Beer's law is obeyed in the range of 5–40 ppm of the metal with an optimum range of 8–40 ppm. The colour is stable for at least one hour. All the common anions are without effect, excepting however, phosphate, carbonate, and cyanide which are tolerated only in traces. Use of tartrate or EDTA helps to mask effectively all the interfering cations excepting copper, iron and vanadium.     

Phthaleinviolett als Indicator in der Chelatometrie

Zusammenfassung Durch Dünnschicht-Chromatographie auf Maisstärke konnte die Trennung und der Nachweis von Pb²⁺-, Ag⁺- und Hg₂ ²⁺- sowie Ba²⁺-, Sr²⁺-, Ca²⁺- und Mg²⁺-Ionen durchgeführt werden. Als Fließmittel diente Aceton-3 n Salpetersäure (11) bzw. Aceton-3 n Salzsäure (23). 1 · 10^–8 bis 5 · 10^–9 Äquivalente der Ionen konnten nachgewiesen werden.

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Summary Separation and identification of Pb²⁺, Ag⁺, Hg²⁺ and Ba²⁺, Sr²⁺, Ca²⁺, Mg²⁺ ions has been achieved by thin-layer chromatography on maize starch, using acetone — 3 n nitric acid (11) resp. acetone — 3 n hydrochloric acid (23) as a solvent. 1 · 10^–8 to 5 · 10^–9 equivalents of the ions could be detected.

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Ein Teil der Versuche für diese Arbeit hat die Chemie-Absolventin Ana Bem ausgeführt, wofür ihr auch bei dieser Gelegenheit gedankt sei.     

Ionic strength dependence of formation constants. Part 4. Potentiometric study of the system Cu2+-Ni2+-citrate

Summary The ternary Cu²⁺-Ni²⁺-citrate (cit^3–) system was investigated potentiometrically in aqueous solution, at different temperatures, 10t45°C, and ionic strengths, 0.03I0.8 mol dm^–3, using potassium nitrate or tetraethylammonium bromide as background salt. Since the citrate anion forms weak complexes with potassium, the stability constants here reported differ according to whether the potassium association is considered or not. In the presence of both Cu²⁺ and Ni²⁺, the mixed metal species, [CuNi(cit)₂H_–2]^4– is formed with citrate in solution, in addition to the various binary complexes. We have obtained the dependence for all the formation constants on ionic strength and temperature. The previous suggestions concerning a general equation for describing the dependence, log =f(I), are confirmed; from the study of log =f(T) we have obtained the values of thermodynamic parameters. The dependence of H on ionic strength is discussed.     

Application of l-cysteine-capped nano-ZnS as a fluorescence probe for the determination of proteins

Nanometer-sized l-cysteine-capped ZnS particles have been synthesized and used as a fluorescence probe to investigate the effect of proteins on fluorescent intensity. With =190 nm, maximum and constant synchronous fluorescence enhancement was produced at 267 nm and pH 5.12 in the presence of proteins. A highly sensitive synchronous fluorescence method for the rapid determination of proteins has been developed. Under optimum conditions, calibration graphs are linear over the range 0.03–8.0 g mL^–1 for bovine serum albumin (BSA), 0.01–6.0 g mL^–1 for human serum albumin (HSA), 0.05–8.0 g mL^–1 for -globulin (-G), and 0.04–4.0 g mL^–1 for ovalbumin, respectively. The relative standard deviations of seven replicate measurements were 1.75% for 1.0 g mL^–1 BSA, 1.90% for 1.0 g mL^–1 HSA, 1.65% for 1.0 g mL^–1 -G, and 2.32% for 1.0 g mL^–1 ovalbumin.     

Selective Kinetic Determination of Cu2+ with Tetraazamacrocyclic Bis(Methylphosphonate) Ligand (Dipon)

A new macrocyclic ligand, 1,4,8,11-tetraazacyclotetradecane-1,8-bis(methylphosphonic acid) (refered to as dipon) exhibits high thermodynamic and kinetic selectivity for Cu²⁺ compared to other transition metal ions. The initial-rate method (=310nm, pH=3.75, c_L4.6×10^–3molL^–1) was chosen as an optimal experimental approach in order to achieve maximum sensitivity of determination. The dynamic range of the method is (5–200)×10^–6molL^–1, and the detection limit is 2.5×10^–6molL^–1. A standard addition procedure was applied to the kinetic determination of Cu²⁺ to eliminate the effect of interfering ions (e.g. Zn²⁺, Ca²⁺, Mg²⁺, Cd²⁺, Pb²⁺, Mn²⁺, Co²⁺, Ni²⁺, HCO^–₃, Cl^–, SO₄^2–, etc.). The method was tested on artificial and real samples (alloys, pure and spiked mineral water) and gave satisfactory results which are in agreement with the values for some certified materials. The advantage of the proposed method is rapidity, simplicity and robustness in the presence of other metal ions.     

Magnetic properties of transition metal ion cubic 5T2 terms in axial ligand fields

The theory of magnetic anisotropy and susceptibility is worked out for cubic ⁵T₂ terms, the degeneracy of which is partially lifted by a ligand field component of axial symmetry as well as by spin-orbit coupling. Matrix elements are calculated by application of the method of Abragam and Pryce to a set of M.O. based wave-functions. The anisotropy in covalency of the metal-ligand bond and in spin-orbit coupling is taken into account. Numerical values of principal magnetic moments, P and P , are calculated as function of kT/, /, and .The theoretical results are employed in a rigorius analysis of existing single crystal magnetic data on high-spin iron(II) compounds. For (NH₄)₂Fe(SO₄)₂·6 H₂O, =–100 cm^–1, =1070 cm^–1 and =0.8 to 0.6 is obtained. For FeSiF₆·6 H₂O, =–80 cm^–1, =–760cm^–1 at 77.3K and –580 cm^–1 between 20.4 and 1.57K, and 0.7 is derived. No unique fit is possible for K₂Fe(SO₄)₂·6 H₂O. The data are reproduced to better than ±1% in most cases. The limitations of the approach are stressed.

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Zusammenfassung Die Theorie der magnetischen Anisotropie und der magnetischen SuszeptibilitÄt eines ⁵ T ₂ Grundterms im oktaedrischen Ligandenfeld wird für den Fall entwickelt, da\ die Entartung unter dem Einflu\ einer axial-symmetrischen Feldkomponente sowie der Spin-Bahn-Wechselwirkung teilweise aufgehoben ist. Eigenfunktionen werden auf der Grundlage der M.O.-Theorie aufgestellt, Matrixelemente mittels der Theorie von Abragam und Pryce ermittelt. Der Anisotropie der Metall-Ligand-Bindung sowie der Spin-Bahn-Kopplung wird Rechnung getragen. Numerische Werte für die magnetischen Hauptmomente P und P werden in AbhÄngigkeit von kT/, / und berechnet.Die Ergebnisse der Theorie werden für eine genaue Analyse der verfügbaren magnetischen Daten aus Messungen an Einkristallen magnetisch normaler Eisen(II)-Verbindungen verwendet. Für (NH₄)₂Fe(SO₄)₂·6 H₂O werden =–100 cm^–1, = 1070 cm^–1 und = 0,8 bis 0,6 erhalten. Für FeSiF₆·6 H₂O ergeben sich =–80 cm^–1, =–760 cm^–1 bei 77,3K und =–580 cm^–1 zwischen 20,4 und 1,57K sowie 0,7. Die experimentellen Daten können in den meisten FÄllen auf ±1% genau oder besser wiedergegeben werden. Bei K₂Fe(SO₄)₂·6 H₂O gelang keine eindeutige Bestimmung der theoretischen Parameter. Die Grenzen der vorliegenden Behandlung werden kritisch diskutiert.

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Résumé La théorie de l'anisotropie magnétique et de la susceptibilité magnétique est développée pour les termes cubiques ⁵ T ₂, dont la dégénérescence est partiellement levée par une composante à symétrie axiale du champ de ligandes ainsi que par le couplage spin-orbite. Les éléments de matrice sont calculés à l'aide de la méthode d'Abragam et Pryce employée sur un système M.O. des fonctions d'onde de base. On a pris en consideration l'anisotropie de la liaison entre le metal et le ligand et aussi du couplage spin-orbite. Les valeurs numériques des moments magnétiques principaux P et P sont calculées en fonction de kT/, /, et .Les résultats théoriques sont employés dans une analyse détaillée des données magnétiques disponibles sur monocristaux des composés ferreux spin-élevés. Pour (NH₄)₂Fe(SO₄)₂·6 H₂O on a obtenu =–100 cm^–1, =1070 cm^–1 et =0.8 à 0,6. Pour FeSiF₆·6 H₂O on a eu comme résultat =–80 cm^–1, =–760 cm^–1 à 77,3 K et =–580 cm^–1 entre 20,4 et 1,57K avec 0,7. Les valeurs expérimentales sont réprésentées dans la plupart de cas plus précises que ±1%. Au cas de K₂Fe(SO₄)₂·6 H₂O une détermination unique était impossible. Les limites de cette approximation sont discutées.

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Postdoctoral Fellow, Theoretical Chemistry, 1963–1964.     

Electrochemical synthesis of halogen derivatives of bis(1,2-dicarbollyl)cobalt(III)

A convenient electrochemical method for the synthesis of 8,8-dihalogen derivatives of bis(1,2-dicarbollyl)cobalt(III) anion [8,8X₂-3,3-Co(1,2-C₂B₉H₁₀)]^– (X = Cl, Br, I) was developed. The method includes the electrolysis of a solution of alkaline metal halide and tetramethylammonium salt of bis(1,2-dicarbollyl)cobalt(III) in methanol at 50 °C in a one-compartment electrochemical cell with a nickel cathode and platinum anode.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2448–2451, November, 2004.     

The substitution kinetics of the aqua ligand by cyanide ions in [Ru(TPPS)(CO)(H2O)]4−

Summary The reaction between the title compound, ,,,-tetra(p-sulphonatophenyl)porphynatoaquacarbonylruthenate(II), [Ru(TPPS)(CO)(H₂O)]^4–, and CN^- revealed that only the aqua ligand is substituted even in the presence of a large excess of the nucleophile. The pK _a1 was spectrophotometrically determined as 13.4(5) (at 33.2 °C) and kinetically as 13.44(5) (at 33.6 °C). The rate of aqua substitution was determined as 89(4)m ^–1 s ^–1 at 35.1 °C and the activation enthalpy and entropy as 55.44(1) kJ mol^–1 and-27.90(4) J K^–1 mol^–1, respectively.     

Kinetics and mechanisms of the oxidation of the octacyanoniobate(III)ion by oxyanions in alkaline aqueous media

Summary The kinetics and mechanisms of the oxidation of Nb(CN) _inf8 ^sup5– by the oxyanions S₂O _inf8 ^sup2– , BrO _inf3 ^sup– , and IO _inf4 ^sup– have been investigated in alkaline aqueous media (pH 12). The second-order rate constant for the electron transfer reaction between Nb(CN) _inf8 ^sup5– and S₂O _inf8 ^sup2– at 25.0 °C, I = 0.36m (K⁺), is 11.1± 0.3 m ^–1 s ^–1 with H = 30 ± 2kJmol^–1 and S = - 125 + 7JK^–1 mol^–1. The rate constant for the oxidation of Nb(CN) _inf8 ^sup5– by BrO _inf3 ^sup– at 25.0 °C, I = 0.20m (Na⁺), is 2.39 ± 0.08m ^–1 s ^–1 with H = 28 ± 2kJmol^–1 and S = -139 ± 7JK^–1mol^–1. The oxidation of Nb(CN) _inf8 ^sup5– by IO _inf4 ^sup– proceeds by two parallel pathways involving the monomeric IO _inf4 ^sup– ion and the hydrated dimer H₂I₂O _inf10 ^sup4– . The second-order rate constant for the oxidation of Nb(CN) _inf8 ^sup5– by monomeric IO _inf4 ^sup– at 5.0 °C, I = 0.050m (Na⁺), is (3.3 ± 0.6) × 10³ m ^–1 s ^–1 with H = 75 ± 6 kJ mol^–1 and S = 94 ± 15 J K^–1 mol^–1, while the rate constant for the oxidation by H₂I₂O _inf10 ^sup4– is (1.8 ± 0.1) × 10³ m ^–1 s ^–1 with H = 97 ± 5 kJ mol^–1 and S = 166 ± 16 J K^–1 mol^–1 under the same reaction conditions. The rate constants for each of the oxidants employed display specific cation catalysis with the order of increasing rate constants: Li⁺ < Na+ < NH _inf4 ^sup+ < K⁺ < Rb⁺ < Cs⁺, in the same direction as the electronic polarizability of the cations. The results are discussed in terms of the outer-sphere electron-transfer processes and compared with the corresponding data and mechanisms reported for other metal-cyano reductants.     

Kinetics of Free Radical Generation in the Catalytic Oxidation of Methanol

The formation of free radicals over the surface of platinum-containing catalysts in the methanol oxidation reaction depending on the temperature, the composition of the reaction mixture, and the procedure used for introducing platinum was studied by the matrix isolation method technique. The nature and transformations of surface intermediates depending on the temperature and the presence of oxygen in the gas phase were studied by Fourier transform IR spectroscopy. The main surface intermediate was the methoxy group. The following three types of these groups were stabilized in alumina-based catalysts: (I) CH₃O–Al_oct (_s(–) = 2806 cm^–1), (II) CH₃O–Al_tetr (_s(–) = 2825 cm^–1), and (III) CH₃O < (Al)₂ (_S(–) = 2845 cm^–1, _s(–) = 1460 cm^–1, _s(–) = 1440 cm^–1, r _|| (₃) = 1185 cm^–1, and (–) = 1095 cm^–1). At the same time, isolated methoxy groups (_as(–) = 2997 cm^–1, _as(–) = 2959 cm^–1, _s(–) = 2857 cm^–1, and (₃) = 1450 cm^–1) and hydrogen-bonded groups ((–) = 3400–3550 cm^–1), which resulted from chemisorption at siloxane bridges, were stabilized in silica gel–based catalysts. It was found that CH₃O and CH₃OO radicals were formed only over the surfaces of pure supports (SiO₂ and Al₂O₃) and their mechanical mixtures with platinum. The total concentration of radicals was described by an extremal function of the composition of reactants, whereas the relative concentration depends on the nature of the support. This is conceivably due to the effect of coordinatively unsaturated cations of the support, which are formed by dehydroxylation in the course of catalyst pretreatment. An increase in the rate of formation of gas-phase radicals on mixed catalysts was explained by special properties of the platinum/support interface region, at which surface intermediates were formed in superequilibrium concentrations under reaction conditions.     

Kinetics and mechanism of oxidation ofd-xylose by Mn(III) pyrophosphate

The oxidation ofd-xylose by Mn(III) pyrophosphate in sulphuric acid has been found to be first order with respect to [Mn(III)]. Variation of rate with [d-xylose] suggests the rapid formation of reversible cyclic complex between Mn(III) and id-xylose, which further disproportionates in a slow rate determining step. Oxidation rate has been found to increase with [H⁺]. Retardation of rate due to [pyrophosphate] and increase due to [Mn(II)] have been also observed. The value of thermodynamic parameters E, S, and G have been found to be 17.6±0.1 kcal/mole, –10.1±0.1 e.u. and 20.6±0.1 kcal/ mole respectively. A mechanism involving a free radical has been proposed for the reaction under study.     

Aktivierungsanalytische Gem?ldeuntersuchungen

Zusammenfassung Aktivierungsanalytisch wurden die Spurengehalte an Mn, Cu, Ba, Cr, Ag und Sb im Bleiweiß von Gemälden der Alten Pinakothek bestimmt. In Modellversuchen wurde ein aus radiochemischer Trennung und -Spektrometrie kombiniertes Analysenverfahren ausgearbeitet. Die Nachweisgrenzen lagen bei 5 · 10^–10 g für Ba, 2 · 10^–10 g für Cr, 10^–10 g für Ag und Cu, 10^–11 g für Mn und Sb. Für eine Analyse standen zum Teil nur 10 g Bleiweiß zur Verfügung. Es wurde vorwiegend Bleiweiß aus Gemälden venezianischer und niederländischer Meister des 16. und 17. Jahrhunderts analysiert, wobei sich eindeutige Unterschiede im Mn-, Ag- und Sb-Gehalt von venezianischem und niederländischem Bleiweiß ergaben. Modernes und altes Bleiweiß zeigen große Unterschiede vor allem im Cu- und Ba-Gehalt; dies kann zur Fälschungserkennung dienen.

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Summary Trace concentrations of Mn, Cu, Ba, Cr, Ag, and Sb in white-lead samples of paintings of the Alte Pinakothek were determined by activation analysis. In model experiments an analytical method comprising radiochemical separation and -spectroscopy was developed. The limits of identification were about 5 · 10^–10 g for Ba, 2 · 10^–10 g for Cr, 10^–10 g for Ag and Cu, 10^–11 g for Mn and Sb. Partly there were available only 10 g of white lead for one analysis. Predominately white-lead samples from paintings of Venetian and Dutch masters of the 16th and 17th centuries were analysed. In these samples unambiguous differences were found in the Mn, Ag, and Sb concentrations. Modern and old white lead show great differences mainly in Cu and Ba concentrations; this may be used for the recognition of forgeries.

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Auszugsweise vorgetragen auf der Tagung in Lindau. Lux, F., u. L. Braunstein: Angew. Chem. 78, 720 (1966).

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Auszug aus der von der Fakultät für Allgemeine Wissenschaften der Technischen Hochschule München genehmigten Dissertation über Die aktivierungsanalytische Bestimmung des Spurengehaltes im Bleiweiß von Gemälden der Alten Pinakothek des Dipl.-Chem. Lothar Braunstein.

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Herrn Dr. H. Kühn vom Doerner-Institut für Konservierung und naturwissenschaftliche Untersuchung von Kunstwerken, München, sind wir für zahlreiche wertvolle Anregungen, besonders bei der Auswahl der Gemälde, sowie für die Beschaffung der Analysenproben zu besonderem Dank verpflichtet.

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Herrn Prof. Dr. H.-J. Born danken wir herzlich für die Unterstützung dieser Arbeit. Der Bestrahlungsgruppe des FRM unter Leitung von Herrn Dipl.-Phys. G. Rau danken wir für die sorgfältige Durchführung der Bestrahlungen.Dem Bundesministerium für wissenschaftliche Forschung und der Deutschen Forschungsgemeinschaft gilt unser Dank für finanzielle Unterstützung.     

Synthesis and Application of a Novel Poly(Acryl-p-Toluenesulfonamideamidine-p-Toluenesulfonylamide) Chelating Fiber for Preconcentration and Separation of Trace Noble Metal Ions from Solution Samples

A novel poly(acryl-p-toluenesulfonamideamidine-p-toluenesulfonylamide) chelating fiber containing S, N and O elements was synthesized from polyacrylonitrile fiber and p-toluenesulfonamide and used for the preconcentration and separation for traces of Ru(III), Rh(III), Au(III) and Pd(IV) ions from waste water and ore sample solution. The synthesis of this fiber was simple and rapid. The results indicate that 100ngmL^–1 of these ions can be quantitatively enriched by the chelating fiber at a flow rate of 6mLmin^–1 and a pH of 4 and desorbed quantitatively with 20mL of 6molL^–1 HCl and 5% CS(NH₂)₂ solution at 50°C (with recovery>95%). A 50 to 1000-fold excess of Ca²⁺, Mg²⁺, Mn²⁺, Co²⁺, Fe³⁺, Cu²⁺, Zn²⁺, and Al³⁺ ions caused little interference in the concentration and determination of the analyzed ions. When the fiber had been reused twenty times, the recoveries of the ions enriched by the fiber were still over 96%. The saturated adsorption capacities of the fiber were in the range of 22–96mgg^–1. The relative standard deviation (RSD) of the method was between 0.70% and 0.84%. Recoveries of a standard added to actual samples were in range of 95–101%. The results obtained for these ions in real solution samples were basically in agreement with the given values, the average errors being below 5.0%. FT-IR spectra show that the existence of –SO₂–Ar, HN=C–NH–, O=C–NH– and –NH–SO₂ functional groups are verified in the chelating fiber. The experiments show that the method is rapid, precise, simple and convenient.     

Kinetics of anation of hexaaquachromium(III) by thiocyanates – specific salt effects

The kinetics of anation of hexaaquachromium(III) by thiocyanates follows the rate law: –d[complex]/dt=k[NCS] (20–40°C, [NCS^–]=0.1–0.6M, I=2.0M, pH=1.0). The specific salt effect has been studied for five media: NaCl, NaBr, NaClO₄, KCl and CsCl. The series of chloride (Na⁺, K⁺ and Cs⁺) salts show a negligible effect on the anation rate. On the contrary, the series of sodium salts (Cl^–, Br^– and ClO ₄ ^– ) reveal a marked difference in the reaction rate. The anation rate decreases sharply with the ionic strength increase (I=0.2–2.0M, NaCl). The results were interpreted within the frame of fast equilibria of ion-pair formation followed by an interchange mechanism step. The difference of reaction rate is a result of competition between anions (thiocyanates and supporting electrolyte anions) to the complex cation at an ion-pair formation process.     

“Titrations” in the submicro-range with microcrystal end-point detection

Summary Drops with increasing volume of a titrant standard solution are put on a microscope slide. One drop of equal volume of a sample solution is then added to all drops. The drops are allowed to evaporate at room temperature and the residues are observed under a microscope. If the end-point is reached, the characteristic crystals of the titrant appear at the periphery of the evaporated drops. Following substances have been determined by this technique: Ca²⁺ (0.4–4.0g) with (NH₄)₂C₂O₄, SO₄ ^2– (0.48–4.8g) with BaCl₂, Ni²⁺ (0.2–2.0g) with dimethylglyoxime, Fe³⁺ (0.6–6.0g) with K₄[Fe(CN)₆], Cl^– (0.15–1.5g) with silver acetate.

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Titrationen im Submikro-Bereich mit Mikrokristall-Endpunktsindikation

Zusammenfassung Tropfen mit zunehmenden Volumina eines Titrationsmittels (Maßlösung) werden auf einen Objektträger aufgetragen. Dazu gibt man gleich große Tropfen einer Probelösung. Man läßt diese bei Raumtemperatur eintrocknen und betrachtet die Rückstände unter einem Mikroskop. Nach Erreichen des Endpunkts erscheinen am Tropfenrand charakteristische Kristalle des Titrationsmittels. Mit dieser Technik wurden folgende Ionen bestimmt: Ca²⁺ (0,4–4,0g) mit (NH₄)₂C₂O₄, SO₄ ^2– (0,48–4,8/gmg) mit BaCl₂, Ni²⁺ (0,2–2,0/gmg) mit Dimethylglyoxim, Fe³⁺ (0,6–6,0/gmg) mit K₄[Fe(CN)₆] und Cl^– (0,15–1,5/gmg) mit Silberacetat.

     

2,3-Dihydroxypyridine Loaded Amberlite XAD-2 (AXAD-2-DHP): Preparation, Sorption–Desorption Equilibria with Metal Ions, and Applications in Quantitative Metal Ion Enrichment from Water, Milk and Vitamin Samples

2,3-Dihydroxypyridine loaded (via –N=N–linker) Amberlite XAD-2 (AXAD-2-DHP) was prepared and characterized by elemental analyses, TGA and FT-IR spectra. It (1g packed in a column of 1cm diameter; surface area 135.5m²g^–1) was found to be an effective solid phase sorbent for enriching Zn²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Co²⁺ at pH 3.5 to 7.0 using flow rates between 1.0–5.0mLmin^–1. For desorption (recovery 97.0–99.8%) of the metal ions, 8 to 10mL of 2.0molL^–1 HCl or 1.5molL^–1 HNO₃ at a flow rate of between 2.0 and 4.0mLmin^–1 were found most suitable. The t_1/2 (time for 50% sorption) is between 2 and 10min when a 50mL solution (containing a total amount of metal of 2mg) was equilibrated with 0.5g of resin. Sorption of all metal ions except Pb²⁺ follows the Langmuir model, whereas for Pb the data fits with the Freundlich model. The sorption capacity is between 60.7 (for Cd) and 406.7 (for Cu) µmolg^–1. The resin can withstand an acid concentration of 6molL^–1 and can be reused for thirty cycles of sorption–desorption. The preconcentration factor varies between 100 and 300. For Cd, Ni and Cu the sorption capacity of 2,3-dihydroxypyridine loaded cellulose is lower than that of the present resin. The tolerance limits of electrolytes, humic acid, complexing agents, Ca²⁺ and Mg²⁺ in the enrichment of all metal ions are reported. The limits of detection are 3.88, 5.37, 8.72, 13.88, 4.71, 1.24, 0.59 and 0.30µgL^–1 for Zn²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Co²⁺, respectively. The calibration curves for flame AAS determination were linear in the ranges 0.018–1.0, 0.067–5.0, 0.2–5.0, 0.9–20, 0.028–2.0, 0.077–5.0, 0.19–10 and 0.1–3.5µgmL^–1, respectively. All the eight metal ions in river and synthetic water samples, Co in vitamin tablets and Zn in milk samples have been quantitatively enriched with Amberlite XAD-2-DHP and determined by flame atomic absorption spectrometry.     

Homo- and heterodinuclear 2,2′-bipyrimidine-bridged complexes

[M(hfacac)₂(bpym)] complexes, where M = Co^II, Ni^II or Zn^II, hfacac = hexafluoroacetylacetonate and bpym = 2,2bipyrimidine; and [Cl₂M(bpym)M(hfacac)₂] complexes, where M = Co^II, Ni^II Mn^II or ZnII M = Ni^II; M = NiII or Zn^II and M = Zn^II; M = Ni^II and M = Co^II have been prepared and characterized by chemical analysis, conductance measurements, IR and electronic spectroscopies and magnetic susceptibility measurements (4.2–292K range). The dinuclear NiII–Ni^II, Co^II–Ni^II and Mn^II–Ni^II complexes are antiferromagnetic, with an intramolecular exchange parameter, J, of –2.3–8.9cm–1. Co^II and Mn^II are in a high spin state. The low temperature effect observed in monomers and in Ni^II–Zn^II dimers is considered a consequence of either an intermolecular antiferromagnetic interaction or the zero-field splitting in NiII.