Cleavage by halogens of carboncobalt bonds in organometallic complexes of cobalt(III) : II. Organobis(dimethylglyoximato)cobalt(III) complexes

The reaction between organocobaloximes and ICl in chloroform has been studied. In absence of an excess of added chloride ion the reaction is electrophilic in character; in presence of an excess of chloride ion both oxidative dealkylation and radical attack can occur.     

Thermal studies on oxalate complexes. II. Complexes of iron (III) and chromium (III)

The decomposition of solid K₃[Fe(C₂O₄)₃] · 2 H₂O and K₃[Cr(C₂O₄)₃] · 3 H₂O has been studied using TGA and DSC. After dehydration, the chromium compound was found to decompose by the loss of CO in two steps, the loss of CO₂ and additional CO, and finally the loss of CO₂. The final product appears to be either K₃CrO₃ or the mixed oxides of chromium and potassium. Kinetic parameters and enthalpy data are presented for these reactions. In the case of K₃[Fe(C₂O₄)₃] · 2 H₂O, dehydration is followed by the loss of CO₂ and CO, CO₂ alone, and finally CO. The final product appears to be a basic carbonate of the type K₃[FE(O)₂(CO₃)]. Kinetic and thermal data are presented for most of these decomposition reactions.     

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 and X-ray diffraction investigations of some lanthanum(III) and neodymium(III) oxide-alkali persulfate binary systems

Different molar ratios of La₂O₃ or Nd₂O₃:Na₂/K₂S₂O₈ have been prepared, and the results of their TG and DTA investigations, under an atmosphere of static air, are reported. The effects of either La₂O₃ or Nd₂O₃ on the thermal decomposition of the persulfates from ambient to 1050°C, using a derivatograph, have been studied. It has been found that La₂O₃ lowers the initial decomposition temperatures of these alkali persulfates through catalytic activity. Nd₂O₃ shows little or no catalytic effect and therefore it acts as an insulator. Intermediate and final products are identified by X-ray diffraction analysis. The stoichiometric molar ratios of the solid state reactions are 1:3::R₂O₃:M₂S₂O₈. (R = La or Nd. M = Na or K), which give double salts of formulae: NaLa(So₄)₂, KLa(SO₄)₂, NaNd(SO₄)₂, and KNd(SO₄)₂. No sulfates or oxysulfates of lanthanum or neodymium have been identified.     

Photolysis of methyl(triphenylphospine)gold(I)

Methyl(triphenylphosphine)gold(I) reacts with chloroform under UV irradiation to give methyl and solvent-derived radicals in triplet pairs showing CIDNP. An S_H2 substitution by methyl radicals at the gold centre is observed.     

Thermal decomposition of some dihalotetramminecobalt(III) nitrates

The thermal decomposition of some dihalotetramminecobalt(III) nitrates [tetrammire =(NH₃)₄, (NH₃)₂(en), (NH₃)(dien), (en)₂, (pn)₂, (trien), etc.] with different degrees of chelation was studied by various thermoanalytical techniques. A partial oxidation—reduction was observed for these complexes above 200°C which was indicated by a rapid TG mass-loss and a large exothermic DTA peak. A relative order thermal stability is reported.     

Mössbauer and infrared spectroscopic studies of some organotin(IV) schiff base complexes

Several organotin(IV) complexes with quadri- and terdentate anionic Schiff base ligands have been investigated in the solid state using ¹¹⁹Sn Mössbauer and IR spectroscopies, Mössbauer parameters derived from both zero-field and magnetically perturbed spectra suggest that the R₂Sn(Salen)(R = Me, Et, Ph) and Me₂Sn(Saldap-2OH) complexes have similarly distorted trans-octahedral structures. However, in Ph₂Sn(HSaldap-2-O) the ligand appears to be only terdentate, leading to a penta-coordinate structure similar to those of the R₂Sn(Sal-N-2-OC₆H₄) derivatives (R = Me, Ph). For Ph₃Sn(Sal-N-2-OC₆H₄) the asymmetry parameter of the electric field gradient is close to unity, confirming a mer-octahedral configuration for this complex.     

An electrochemical study of the adsorption of two isomeric chromium(III) complexes on mercury electrodes: Thioether as an anchoring group

Cyclic voltammetry and chronocoulometry were utilized to examine the electrochemistry and adsorption on mercury of two isomeric complexes of Cr(III) with a multidentate ligand bearing a thioether group, thiobis(ethylenenitrilo) tetraacetic acid, S[CH₂CH₂N(CH₂COOH)₂]₂. One isomer contains a sulfur-chromium bond and is exceedingly strongly adsorbed. The second isomer lacks this bond and is adsorbed much less strongly. Back-bonding from chromium to sulfur is argued to play an important role in the adsorption of the first isomer. Upon reduction, both isomers yield the same Cr(II) product. A dimeric form of the second isomer in which the two Cr(III) centers are bridged by an acetate group is proposed to form at certain pH values. The different coordination environments of the two Cr(III) centers in the dimer cause them to be reduced at different potentials.     

Preparation and electronic spectra of some alkyl- and aryl(2,2′-bipyridine)platinum(II) complexes

A series of alkyl- and aryl-(2,2′-bipyridine)-platinum (II) complexes has been prepared by displacement of the diene ligand in the corresponding cyclooctadiene complexes with 2,2′-bipyridine. Dimethyl(1,10-phenanthroline)platinum(II) was prepared in an analogous way. The electronic spectra of the complexes contain metal to ligand charge transfer bands whose energy is dependent on the nature of the substituents on platinum and on the solvent. It is suggested that π-bonding is important in the phenyl—platinum bond.     

Stability and thermodynamics of La(III)-, Pr(III)-, Nd(III)-, Gd(III)- and Eu(III)-p-nitrobenzaldehyde thiosemicarbazone systems

Three complexes containing bidentate N-2,3-dimethylphenylglycine, (2,3-HDPG), N-2,4-dimethylphenylglycine, (2,4-HDPG) and N-2-ethylphenylglycine, (2-HEPG) acids have been prepared and characterized. These compounds have the general formula Zn(2,3-DPG)₂·2 H₂O, Zn(2,4-DPG)₂ and Zn(2-EPG)₂·2 H₂O, respectively. The structure of the complexes as inferred from their chemistries have been found to be compatible with the infrared spectral data. The thermal behaviour of these complexes has been studied from their TG, DTG and DSC diagrams obtained in a dynamic atmosphere of pure air. Heats of dehydration have been calculated from DSC curves.     

Reactions of some electrophilic olefins with (carbonato)bis(triphenylphosphine)- and (carbonato)bis(triphenylarsine)-platinum complexes

Carbonato complexes L₂PtCO₃ (L = PPh₃ or AsPh₃) react with certain electrophilic olegins, such as 1,1-dicyanoolefins, under mild conditions to liberate CO₂. The reaction of L₂PtCO₃ with tetracyanoethylene at room temperature is solvent dependent, and in alcoholic solvents, in contrast to an earlier report, the dicyano complexes, L₂Pt(CN)₂, and tricyanoethenolato complexes, L₂Pt(CN) [OC(CN)C(CN)₂] have been isolated and identified.     

Thermal studies on purine complexes. I. Thermal behaviour of some xanthine complexes of cobalt(II), copper(II) and cadmium(II)

Cobalt, copper and cadmium xanthinate tetrahydrates have been prepared in aqueous medium, and characterized on the basis of elemental analysis, IR and ¹HNMR studies. The thermal behaviour of these compounds has been studied using TG, DTG and DSC techniques. Heats of dehydration have been calculated from DSC curves.     

The electrochemical behavior of Os(II) complexes with α,α′-bipyridine and o-phenanthroline in non-aqueous solvents

The electrode reactions of Os(II) complexes with α,α′-bipyridine and o-phenanthroline have been studied in non aqueous solvents. Tris bipyridine and tris phenanthroline complexes of Os(II) give one-step oxidation waves and three-step reduction waves, while bis bipyridine complexes of Os(II) containing py₂, en, CN₂, Cl₂ and Br₂ as mixed ligands give one-step oxidation waves and two-step reduction waves. Most of these waves correspond to reversible single electron transfers. It is noticed that the half-wave potentials or the peak potentials of bis bipyridine complexes are shifted to more negative direction than those of the tris complex in both oxidation and reduction processes. This is attributable to less electron with drawing nature of substituted ligands than bipyridine. These potential data, the shifts of E_1/2 or E_p from those of tris complexes, and δE*, the potential difference between two consecutive single electron waves, are discussed in terms of molecular orbital scheme.     

Mixed ligand complexes in vinyl polymerization—II: [NN′-ethylenebis(salicylideneiminato)] (benzoylacetonato)cobalt(III) as an initiator

The polymerization of methyl methacrylate initiated by a mixed ligand complex. [NN′-ethylenebis(salicylideneiminato)](benzoylacetonato)cobalt(III) has been studied in bulk and in benzene at 70° and 80°. The rate of polymerization is proportional to (concentration of the chelate)${}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and the monomer exponent is close to 1.5. The activation energy and the kinetic and transfer constants are evaluated. A free radical mechanism has been proposed.     

A correlation between spin state and electrochemical electron-transfer rate for tris(N,N-disubtituted dithiocarbamato) iron(III) complexes

The electrochemical electron-transfer rate constants for the redox systems Fe(IV)L₃⁺/Fe(III)L₃ (L=N,N-disubstituted dithicarbamate ion) and Fe(III)L₃/Fe(II)L₃^? with a variety of substituents were measured at a platinum electrode in acetonitrile with the galvanostatic double-pulse method. It is known that each of the Fe(III) complexes exists both in a highspin state ⁶A₁ and a low-spin state ²T₂ in equilibirium of which position is widely changed by a subtle change in substituent. The standard rate constants for Fe(IV)L₃⁺/Fe(III)L₃ were larger or smaller than those for Fe(III)L₃/Fe(II)L₃^? according as the Fe(III)L₃ complexes are predominantly low- or high-spin complexes. Since the Fe(IV) and Fe(II) complexes are low-and high-spin complexes respectively, these findings suggest that electrochemical electron-transfer reactions accompanied by a spin-state change are slower than those without it. Such spin-state effect on electrode reactions has rarely been discussed so far.     

Polarographic studies on bipyridine complexes: III. Polarography of tris(2,2′-bipyridine) complexes of chromium(I), chromium(0), vanadium(0), titanium(0) and molybdenum(0)

Polarograms and cyclic voltammograms for tris(2,2′-bipyridine) complexes of V(0), Cr(0), Cr(I), Ti(0) and Mo(0) in N,N-dimethylformamide are reported. The reversible half-wave potentials for the following redox systems in lower oxidation states are determined: Cr(?I)/Cr(?II), Cr(?II)/Cr(?III), V(I)/V(0), V(0)/V(?I), V(?I)/V(?II), V(?II)/V(?III), Ti(0)/Ti(?I), Ti(?I)/Ti(?II), Mo(?I)/Mo(?II) and Mo(?II)/Mo-(?III). On the basis of the half-wave-potential shift caused by the methyl substitution of ligands, it is concluded that each excess electron of the reductant species of the redox systems, V(bipy)₃^?/V(bipy)₃^2?, Cr(bipy)₃/Cr(bipy)₃^?, Cr(bipy)₃^?/Cr(bipy)₃^2? and Cr(bipy)₃^2?/Cr(bipy)₃^3? (bipy=2,2′-bipyridine), occupies a ligand π^*-orbital and that of the V(bipy)₃²⁺/V(bipy)₃⁺ and V(bipy)₃⁺/V(bipy)₃ systems a metal t_2g-orbital. The apparent π-character of the excess electron of the redox systems Cr(bipy)₃⁺/Cr(bipy)₃ and V(bipy)₃/V(bipy)₃^? is discussed. It is pointed out that the relative electron affinities of trisbipyridine complexes can be determined from the half-wave potential data. The lowest π^*-orbitals of V(bipy)₃^?, Cr(bipy)₃ and Fe(bidy)₃²⁺ become higher in this order. This suggests that the electrostatic interaction between a π^*-electron and the residual charge on the central metal ion predominantly accounts for the observed π^*-level shift.     

Formation equilibria of copper(II) complexes with some pyridinols in various solvents

Complexation of copper(II) with two different pyridinols in three solvents has been studied by visible spectrophotometry and flow-microcalorimetry. The influence of the solvent on tautomeric equilibrium of the ligand, on distribution, on stability and on formation enthalpies of the main complex species is discussed.     

The behaviour of alkylcobalt carbonyls under “oxo” conditions

Alkylcobalt carbonyls, synthesized under oxo conditions from alkyl halides and sodium tetracarbonylcobaltate, give the corresponding aldehydes on treatment with CO and H₂. The alkylcobalt carbonyls do not isomerize significantly under oxo conditions. Alkylcobalt carbonyls prepared from alkyl halides and sodium tetracarbonylcobaltate or from orthoformic esters dicobalt octacarbonyl, CO and hydrogen do not isomerize even in the presence of an excess of olefin.     

Polarographic studies on the electrode kinetics of the nickel(II) complexes with glycine and some of its derivatives: I. glycine complexes

D.C. polarograms of the Ni(II)-glycine complexes were measured with varying pH values at constant total glycine concentration (0.05 M) and conversely with varying total glycine concentration at constant pH values (3.5, 4.5, 7.5 and 9.5). The current—voltage curves obtained were analysed to determine the limiting currents, the transfer coefficients, and the half-wave potentials, by using the non-linear least squares method. From the dependence of the half-wave potentials on the free glycine concentration, the mechanism of the electrode processes was elucidated. It was shown that the first wave corresponded to the reduction of the Ni²⁺ aquo-complex, the second to the NiG⁺ complex, the third to the NiG₂ complex and the fourth to the NiG^?₃ complex. The kinetic parameters for the four charge transfer processes were determined.The second and third waves were kinetic in character and the rate constants of the dissociation and association reactions between NiG⁺ and NiG₂ and between NiG₂ and NiG^?₃ were determined by analysing the dependence of the kinetic limiting currents on the free glycine concentration.