Complexation reaction of metal ions with peptide systems. Part II. Potentiometric studies of the complexes of glycyl-DL-valine with Gd, Dy, Er and Yb

The stable complexes of amino acids with rare earths have found importance in the separation of these metals¹. The complexation reactions of a number of dipeptides with copper and nickel have been reported in the literature^{2 – 9}; but little work appears to have been done with rare earth metals. This paper is a continuation of our earlier communication¹⁰, and deals with the study of complexes of Gd³⁺, Dy³⁺, Er ³⁺ and Yb³⁺ with Glycyl-DL-valine. The Calvin—Bjerrum^{11, 12} pH titration technique, as modified by Irving and Rossotti¹³, has been employed.     

Thermal and chromatographic behaviour of metal complexes. Part II. Complexes of platinum(II) with dipeptide ester

Experimental measurements of the rate of reduction of particles of Carol Lake and Kiruna ores have been made using pure hydrogen and pure carbon monoxide and mixtures of these two gases. The temperature range covered was 773–1143 K and throughout this range the reduction rate with hydrogen was greater than that with carbon monoxide. A retracting core model was found to best fit the experimental data even when granules of 9 × 10^?4 m diameter were used. Reduction with gas mixtures of hydrogen and carbon monoxide give rates intermediate between those of the pure gases.     

Thermal and chromatographic behaviour of metal complexes. Part III. Complexes of palladium(II) with iminodiacetic acid

A study of the thermal properties of the complexes formed between Pd(II) and iminodiacetic acid (IDA) and the chromatographic analysis of their thermal decomposition products have been carried out. The dehydration of the isolated compounds is detected above 100°C. The decarboxylation process of the COO^? groups takes place yielding CO₂ and CO simultaneously or consecutively if they are not coordinated, respectively. The formation of gases (methane, ethane, etc.) is also observed.     

Voltammetric study of humic and fulvic substances: Part II. Mechanism of reaction of the Pb-fulvic complexes on the mercury electrode

A model is presented for the electrode process corresponding to the reduction of Pb(II) complexed by fulvic substances. The various factors which may affect the polarographic results are discussed and a mathematical expression is given for the polarographic wave. The influence of various parameters was tested. It was found that the formation of complexes both present in solution and adsorbed at the surface of the electrode is the predominant factor which affects the potential of the wave. Moreover, the diffusion coefficient of the complexes is much lower than that of free lead. We discuss the nature of the complexes adsorbed at the electrode surface and the implications of the findings of this work when using the polarographic methods for the determination of the complexing ability of waters.     

Thermal studies on metal dithiocarbamato complexes. A review

In the present review, the work done on thermal studies of metal dithiocarbamato complexes during the period 1969–1982 are given. The thermal studies include thermogravimetry, differential thermogravimetry, differential thermal analysis, differential scanning calorimetry and mass spectrometry. Fifty-two references are included.     

Electrode kinetics of the metal complexes with aminopolycarboxylic acids: Part II. Cadmium-ethylenediamine-N,N,N′,N′-tetraacetate (EDTA) complexes

The d.c. polarographic current-potential curves of Cd(II)-EDTA complexes were examined in the pH range 0.5–10.0, to elucidate the mechanism of their electrode processes and to determine the relevant electrochemical kinetic parameters. It was shown that the first wave observed below pH 3 at ?0.58 to ?0.65 V vs. SCE is the reversible reduction wave of Cd(II) aquo-ion with kinetically-controlled limiting current, and the second wave observed above pH 1.5 at ?0.75 to ?1.21 V vs. SCE corresponds to the simultaneous irreversible reduction of four complex species, CdH₃L⁺, CdH₂L, CdHL^? and CdL^2?, where CdH_pL^(p?2)+ and L^4? denote the protonated complex species with p protons and the unprotonated EDTA ion, respectively. Analysis of the dependence of limiting current on the hydrogen ion concentration led to the conclusion that the preceding reaction determining the behaviour of limiting current is CdH₃L⁺?Cd²⁺+H₃L^? with k₃^d=6.3×10² s^?1 and k₃^f=3.3×10⁶ s^?1M^?1, where k₃^d and k₃^f are the dissociation and formation rate constants, respectively. On the other hand, from analysis of the dependence of half-wave potentials of the second wave on the hydrogen ion concentration, the kinetic parameters of the four complex species were evaluated, and are given in Table 1. Further, it was shown that the cathodic rate constants of these four charge transfer processes at some reference potential together with those of Cd(II)-HEDTA complexes fulfil the linear free energy relationship.     

Transition metal–carbene complexes XCVII. π-cyclopentadienyldicarbonylmethylphenylcarbenerhenium

Addition of P(OMe)₃ to [Rh(η³?C₃H₅) (CO)₂] gives [Rh(η³?C₃H₅){P(OMe)₃}₃]; this reacts with hydrogen or silanes to form a species which is an effective hydrogenation catalyst for olefins and a hydrosilylation catalyst for terminal olefins, aldehydes and ketones.     

Alkylation reactions with organometallic compounds : IV. The reaction of tris(triphenylphosphine)methylcobalt with diphenylacetylene

Tris(triphenylphosphine)methylcobalt;(Ph₃P)₃CoCH₃, reacts with diphenyl-acetylene to give α-methylstilbene as the sole addition product.(Ph₃P)₃CoCH₃ can be used as an alkylation reagent in ethers or in aromatic solvents.     

Antiferromagnetic complexes involving metalmetal bonds : I. Synthesis and molecular structure of an antiferromagnetic dimer with a CrCr bond

The binuclear complex (C₅H₅)₂Cr₂(S)(SCMe₃)₂ was prepared by refluxing a solution of chromocene and t-butylmercaptane in heptane. The structure of the product was determined by single crystal X-ray diffraction. The chronium atoms are linked by a sulphide bridge (SCr 2.24 Å;, <CrSCr 74.1° and two SCMe₃ bridges (CrS 2.38 Å;, <CrSCr 68.3–69.3°). The two cyclopentadienyl ligands (CC 1.41 Å;, CrC 2.23 Å;) are in apical positions, their ring planes being parallel to each other. The complex is an antiferromagnet (?2J cm^?1) despite the small CrSCr angles and short chromiumchromium distance (2.689 Å;) indicative of strong CrCr bonding.     

A study of the reaction of N-chlorosuccinimide with indoles and its analytical application

The reaction of N-chlorosuccinimide with indole and few of its derivatives in acid medium has been studied. The purified products have been identified by TLC, elemental analysis and infrared studies, and a reaction mechanism is proposed on the basis of the results. The reaction proceeds smoothly and consistently, and can be used for microdetennination of indole and its derivatives.     

Boron hydride reduction of transition metal—acetyl complexes

Acetyl complexes of iron(II) and ruthenium(II) of the type (π-C₅H₅)(CO)LM(COCH₃), where L = PPh₃, P(OPh)₃, P(cyclohexyl)₃, PMe₂Ph or CO for M = Fe, and PPh₃ for M = Ru, are rapidly reduced to the corresponding ethyl complexes by BH₃ · THF or B₂H₆/C₆H₆. In some cases hydrido complexes of the type (π-C₅H₅)(CO)LMH are also formed. The reaction has been studied by use of ¹H NMR and the spectrum of (π-C₅H₅)(CO)(PPh₃)FeC₂H₅, which shows several unusual features, is discussed in detail. It is suggested that the rate of reduction increases with increasing electron density at the metal centre.Acetyl complexes of other transition metals, i.e. Ir, Pt, Pd, Co and Mo, are also reduced to the corresponding ethyl compounds by B₂H₆/C₆H₆.     

Oxidimetric determination of methionine and its metal complexes with chloramine-B and dichloramine-B

Simple, rapid, and reproducible methods for the determination of methionine (HMt) and its metal complexes, [NiMt]ClO₄₊ and Na[AgMt₂], in aqueous solutions have been developed, based on their oxidation with chloramine-B and dichloramine-B at room temperature. The direct titration, with a visual or potentiometric endpoint, involves a two-electron change corresponding to the formation of methionine sulfoxide. Several amino acids and common anions and cations do not interfere under these conditions. In the back-titration procedure methionine and its complexes are oxidized by excess CAB in 0.1 N NaOH medium with a four-electron change corresponding to the formation of methionine sulfone. The amino acid and its complexes are, however, oxidized to the respective nitrile, with excess DCB with an eight-electron change.     

Competitive transport of alkali metal ions from aqueous media into toluene solutions of 2-(sym-dibenzo-16-crown-5-oxy)-decanoic acid. A comparative study

Competitive permeation of alkali metal ions from an alkaline source phase into or through a toluene phase facilitated by the lipophilic crown ether carboxylic acid 2-(symdibenzo-16-crown-5-oxy)-decanoic acid is studied in liquid—liquid extraction, bulk liquid membrane transport, and emulsion liquid membrane transport. Most rapid transport was obtained in emulsion liquid membrane experiments. Some differences in selectivity orders for alkali metal permeation were observed for the three separation techniques.     

Rare earth transition metal sulfides,LnMS3

Ternary rare earth transition metal sulfides LnMS₃ with Ln = La, Nd, and Gd, and M = V and Cr; as well as Ln = La and M = Mn, Fe, Co, and Ni have been prepared and characterized. The vanadium and chromium sulfides crystallize in a monoclinic layer structure isotypic with LaCrS₃, while the other LnMS₃ sulfides crystallize in a hexagonal structure. Chemical shifts of the metal K-absorption edge and XPS binding energies of core levels indicate that the transition metal is trivalent in the V and Cr sulfides, while it is divalent in the Mn, Fe, Co, and Ni sulfides. Electrical and magnetic properties of the sulfides are discussed in terms of their structures and the electronic configurations of the transition metal ions.     

A polarographic study of some complexes of Tl(I) with polyoxa macrocyclic ligands

The log β₁ values at 25° for the reaction in aqueous solution of Tl(I) with 15-crown-5, benzo-15-crown-5, 18-crown-6 and dicyclohexyl-18-crown-6 (isomer cis-syn-cis) have been determined by d.c. and a.c. polarographic measurements.     

Thermal studies on 2,6-xylyliminodiacetato compounds of some transition metal ions

Some new 2,6-xylyliminodiacetato compounds of Mn(II), Fe(III), Ni(III), Zn(II) and Cd(II) have been prepared in aqueous media. The thermal behaviour of these compounds has been studied by TG, DTG, and DSC techniques. Heats of dehydration have been calculated from the DSC curves.     

Fluoride complexes of the alkali metal ions

Measurements by fluoride ion-selective electrode potentiometry on the very weak monofluoride complexes of the alkali metal ions in aqueous solution at 25°C and an ionic strength of 1M indicate their stability constants lie in the order Li⁺ > Na⁺ > K⁺ > Rb⁺ ? Cs⁺. Data at varying ionic strengths and temperatures were used to calculate infinite dilution stability constants and enthalpies and entropies of complexation for LiF and NaF.