Some analytical applications of aromatic sulfonyl haloamines: Determination of thiosemicarbazide alone and in its metal complexes with bromamine-B and dichloramine-B

Simple, rapid, and reproducible back titration methods for the determination of thiosemicarbazide (TSC) in free state and in Zn, Cd, Hg, Ni, Pt, and Pd metal complexes with bromamine-B (BAB) and dichloramine-B (DCB) have been developed. The oxidation reaction involves a 12-electron change per TSC molecule in 0.2–1.0 M NaOH and water-acetic acid media with BAB and DCB, respectively. The proposed analytical procedures for the assay of TSC are also useful for computing the number of TSC ligands present in the respective metal complexes. The two aromatic sulfonyl haloamines used, BAB and DCB, were prepared and then characterized by ¹³C FT-NMR spectral data.     

Preparation of chlorodivinylborane transition metal complexes and their nucleophilic substitution at boron

Chlorodivinylborane (I) prepared in situ from boron trichloride and dimethydivinyltin, reactions under photochemical conditions with ironpentacarbonyl and cyclopentadienyldicarbonylcobalt to give (η⁵-chlorodivinylborane)tricarbonyliron (II) and (η⁵-chlorodivinylborane)cyclopentadienylcobalt (III), respectively, in high yield. Complexes II and III readily undergo base-assisted nucleophilic substitution at boron.     

Girard-P derivative of 2-pyridinecarboxaldehyde as analytical reagent. Spectrophotometric determination of copper

The synthesis, characteristics, properties, and reactions with metallic ions of pycolinaldehyde derivatives of Girard-P reagent have been studied. The reagents form complexes with Cu(II), Ni(II), Co(II), Hg(II) and (I), Zn(II), Cd(II), and Fe(III), and (II), which exhibit a good sensibility but whose spectra have the absorption maxima located in the ultraviolet zone. The spectrum of copper complex in the presence of ascorbic acid shows another absorption band at the visible region and this makes the spectrophotometric determination of copper very selective. The influence of the different experimental parameters on the formation of copper complex without ascorbic acid and with this compound was studied, and the optimum conditions for the determination of copper were established. The precision of the procedure, expressed in terms of relative standard deviation, was 1.1%. The method has been tested on “white metal E-8” samples.     

The pzc of mercury in the presence of humic acids and their complexes with aluminium

Variation of the lifetime of a mercury drop with potential was used to determine the pzc of mercury in the presence of soil humic acids and their aluminium complexes. In all cases there was an overall net shift in the pzc in the cathodic direction. Variation in the extent of the shift with pH and concentration indicated greater adsorption of negatively charged species. The shift was smaller in the presence of aluminium humates, probably due to a decrease in the negative charge of the humic acid molecules after complexing. The use of electroanalytical techniques for metal speciation studies in soils and natural water, if humic materials are known to be present, might therefore be limited.     

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.     

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.     

The effect of the central metal charge on the reduction half-wave potentials of d6 metal complexes

A SCF MO calculation is made to obtain the energies of the lowest vacant π-orbitals of tris-2,2′-bipyridine complexes of d⁶ transition metals in various oxidation states. Any overlap of a metal t_2g-orbital and a ligand π-orbital is neglected and the metal ion is considered as a source of an electrostatic potential field. The π-electron system of the three ligand molecules is treated as a whole by taking account of the overlap of 2pπ-AO's belonging to different ligand molecules. When it is assumed that a ligand π^*-orbital is occupied by the electron added in the course of reduction, the results of the calculation and the Born equation for solvation energy together lead to a linear relation between the reduction half-wave potentials of the complexes and the sum of the charges on the central metal ion and the ligand nitrogen atoms. This linear relation is confirmed experimentally by using the available data on the reduction half-wave potentials of the tris-bipyridine complexes of the following d⁶ metals: Ir(III), Fe(II), Ru(II), Os(II), Cr(0), Mo(0), V(?I) and Ti(?II).     

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.     

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.     

Oxidative addition of aryl halides to iridium(I) complexes. A new arylation reagent

Oxidative addition of aryl halides, ArX, to chlorocarbonylbis(triphenylphos-phine)iridium(I) yields iridium(III) aryl complexes, IrCl(X)(Ar)(CO)(PPh₃)₂. The reactivity of the aryl halide decreases in the order I > Br > C1, and electron-withdrawing substituents in the aryl ring accelerate the reaction. The Ir^III compounds may be utilised as arylating agents.     

N,N-Dibromobenzenesulfonamide as an analytical reagent: Determination of thiocyanate and cyanide ions in metal complexes and salts and thiosemicarbazide alone and in its metal complexes

Simple, rapid, and reproducible analytical procedures, for determining thiocyanate and cyanide ions in metal salts and complexes and thiosemicarbazide (TSC) in the free state and in its metal complexes, with the new oxidant, dibromamine-B (DBB), have been proposed. These procedures are also useful for computing the number of ligands present in the complexes. With DBB, CN⁻, and NCS⁻ ions and TSC undergo stoichiometric oxidations with 2-, 8-, and 12-electron changes per ion or molecule, respectively, in water-acetic acid medium. The reagent DBB has been prepared and characterized by elemental analyses and ir and FT-NMR-¹H and -¹³C spectral data.     

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.     

Spectrophotometric determination of BrO3− using the 1,2,4-trihydroxyanthraquinone-3-carboxylic acid as reagent

The reaction between the 1,2,4-trihydroxyanthraquinone-3-carboxylic acid and BrO₃^? in hydrochloric acid medium has been studied spectrophotometrically. The red color of the oxidation product serves as basis for a new method for determination of traces of BrO₃^?, measuring the absorbance at 520 nm. The influence of foreign ions on the determination, the stoichiometry of the reaction, and the nature of the oxidation product, have been reported.     

Transport of alkali metal cations across liquid membranes by crown ether carboxylic acids

Competitive alkali metal transport from an alkaline aqueous source phase through a chloroform phase to an acidic aqueous receiving phase facilitated by nine crown ethers with pendant carboxylic acid groups has been investigated. Transport selectivity is controlled by the size of the polyether cavity of the carrier. Increasing the lipophilicity of the carrier, while maintaining a constant polyether cavity size, enhances the total transport rate but does not affect the selectivity. There is poor agreement between the results of competitive transport and the behavior anticipated on the basis of single cation transport studies.     

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.     

Thermal studies on purine complexes. VII. 8-theophylline derivatives and their silver(I) complexes

Four theophylline derivatives: 8-ethyltheophylline (ETH), 8-isopropyltheophylline (IPH), 8-propyltheophylline (PRH), and 8-phenyltheophylline (FTH) have been synthesized and characterized by spectroscopic techniques and thermal analysis. The melting points of these theophylline derivatives increase with the molecular weight, from 263.8°C (ETH) to 384.7°C (FTH). The values of the fusion enthalpy increase in the same order, from 28.4 kJ mol⁻¹ (ETH) to 36.5 kJ mol⁻¹ (FTH).

The interaction of these theophylline derivatives with Ag(I) has been studied by means of spectroscopic techniques, TG, DTG and DSC. In all cases, the pyrolysis of these compounds gave metallic silver.     

Transition metal complexes with long-chain amines thermal behaviour and crystal structure of (n-CaH2a+1NH2)2ZnCl2

The thermal behaviour of (n-C_aH_2n+1NH₂)₂ZnCl₂ complexes with n = 6, 8, … 16 has been investigated by DSC and by temperature variable IR and X-ray powder diffraction techniques. Complexes with n = 12,14,16 show solid—solid phase transition which are “melting” transitions of the hydrocarbon regions of the structure. The crystal structure of both the low and the high temperature polymorphs is characterized by the piling of sandwiches, each formed by an “inorganic” layer sandwiched between two alkylammonium layers.