Chloro complexes of cobalt(II) in acetone

Equilibria of cobalt(II) perchlorate with lithium chloride in 0.1 M LiClO₄ acetone solution have been investigated by means of potentiometry and spectrophotometry at 25.0°C. By the addition of a large excess of medium salt (LiClO₄), the ionic dissociation of electrolytes are surpressed and the ion-pairs predominate in this medium. It was confirmed that AgAgCl electrode gives rise to the Nernstian response in this medium. The potentiometry reveals the formation of following chloro complexes of cobalt (II): $\text{Co(ClO}{}_4\text{)}{}_2\text{+LiCl}\text{⇌}\text{K}{}_1\text{CoCl(ClO}{}_4\text{)+LiClO}{}_4$$\text{Co(ClO}{}_4\text{)+LiCl}\text{⇌}\text{K}{}_2\text{CoCl}{}_2\text{+LiClO}{}_4$$\text{CoCl}{}_2\text{+LiCl}\text{⇌}\text{K}{}_3\text{LiCoCl}{}_3$Successive formation constants were determined as log K₁ = 5.0 ± 0.3, log K₂ = 6.2 ± 0.3 (log β₂ = log K₁K₂ = 11.15 ± 0.03) and log K₃ = 5.97 ± 0.03. By the spectrophotometric titration at higher concentration of lithium chloride, we have the following equilibrium: $\text{LiCoCl}{}_3\text{+LiCl}\text{⇌}\text{K}{}_4\text{LiCoCl}{}_3$ with formation constant of log K₄ = 2.64 ± 0.05. Absorption spectra of these complexes are presented.     

Free energy of transfer of cobalt(III) complexes from water into water—t-butyl alcohol mixtures

The solubility of trans-(Coen₂Cl₂)₂ReCl₆ has been determined in water and in water +t-butyl alcohol mixtures. By comparzng these values with the solubility of Cs₂ReCl₆ in similar mixtures, values for the difference in free energy of transfer, G _t ^o (i) between water and water + t-butyl alcohol can be calculated for i =[Coen₂Cl₂]⁺ and Cs⁺. The introduction of G _t ^o (Cs⁺) then produces values for G _t ^o (Coen₂Cl₂ ⁺). The difference in G _t ^o (i) for i=[Coon₂Cl]²⁺ in the transition state and i=[Coen₂Cl₂]⁺ in the initiad' tate for the solvolysis of the trans-[Coen₂Cl₂]⁺ ion in water + t-butyl alcohol can be derived from the application of a free energy cycle: using G _t ^o (Coen₂Cl₂ ⁺) determined from the solubility measurements allows the calculation of values for G _t ^o (Coen₂Cl²⁺). G _t ^o (i) in water + t-butyl alcohol for bis (1,2-diamino) cobalt (III) ions are compared with G _t ^o (i) for tetrapyridinecobalt (III) ions.     

Synthesis and characterization of neutral ligand-bridged binuclear dialkylcobalt(III) complexes

A series of neutral ligand-bridged binuclear dialkylcobalt(III) chelates has been prepared. Chelate systems based on monoanions of dimethylglyoxime (dm     

Solvation of inorganic complexes: transfer chemical potentials for mono- and bi-nuclear cobalt(III) complexes to methanol + water mixtures

Solubilities in MeOH--H₂O mixtures at 298.2 K are reported for a number of salts of mono- and bi-nuclear cobalt(III) complexes. From these solubilities and published single ion transfer chemical potentials, on the TPTB (Ph₄P⁺ = BPh^– ₄ ) assumption, transfer chemical potentials have been derived for these mono- and bi-nuclear cobalt(III) complexes. The results and trends are discussed in relation to those for other complexes and ions in these binary aqueous solvent mixtures.     

Kinetics of aquation of cis-aquabromo-bis(ethylenediamine) complexes of cobalt(III) and chromium(III) in binary aqueous mixtures

Summary The kinetics of aquation of cis-[Co(en)₂(H₂O)Br]²⁺ and cis-[Cr(en)₂(H₂O)Br]²⁺ (en = ethylenediamine) were investigated in aqueous mixtures of MeOH, EtOH, i-PrOH and t-BuOH. The values of transfer functions corresponding to the transfer of reactants and activated complex from water to the solvent mixtures were evaluated from kinetic measurements and from solubilities of the complex salt. Analysis of the solvent effect confirmed a common I_d mechanism for the aquation of the Co^III and Cr^III complexes.     

N-monoaryldithiocarbamate cobalt(III) complexes(1)

Summary Diamagnetic cobalt(III) complexes of the type (RHNCS₂)₃Co [R = Ph, XC₆H₄ (X=p-Me,p-OMe,p-Cl,p-Br andp-I) and 2,4-Me₂C₆H₃] have been synthesised by reaction of the corresponding dithiocarbamate ammonium salts and hexaaquocobalt(II) chloride. Ligand field parameters calculated from visible spectral data indicate strong covalent character for the Co-S bond. The i.r. spectral data reveal that the CN bond in these dithiocarbamates has less double bond character compared to the corresponding dialkyldithiocarbamates.     

Activation volumes for peroxodisulphate oxidation of cobalt(III), iron(II) and nickel(II) complexes

Summary Dependences of rate constants on pressure (in aqueous solution up to 1.25 kbar) are reported for peroxodisulphate oxidation of hexacyanoferrate(II), tris(2,2-bipyridyl)iron(II), tris(1,10-phenanthroline)iron(II), bis(1,4,7-triazacyclononane)nickel(II) and bis(1,2-ethanediamine)cysteinatocobalt(III) and its thioglycollato-analogue, and for periodate oxidation of the two last-named complexes. Derived activation volumes are reported and discussed in terms of intrinsic and solvational contributions. Rate laws and pressure effects on reactivity are reported for the reaction of peroxodisulphate with pentacyanoferrates(II) containing N-alkylpyrazinium ligands.     

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.     

Solvation of ligandopentaamminecobalt (III) complexes in dimethyl sulfoxide–water mixtures

The rate constants for the replacement of water from the inner-coordination shell of Co(NH₃)₅OH₂³⁺, I, by dimethyl sulfoxide (DMSO) as DMSO gradually replaced water in the solvation shell of I were found to approach, and finally equal, the water-exchange rate constant of I in aqueous media in accordance with expectation for a dissociative mechanism. Also the rate constants for the replacement of DMSO from the innercoordination shell of Co(NH₃)₅DMSO³⁺, II, by water as water replaced DMSO in the solvation shell of II were found to approach, and approximately equal, the DMSO-exchange rate constant for II in liquid DMSO in accordance with expectation for a dissociative mechanism. The DMSO-exchange rate constant for II in liquid DMSO was determined and found to be equal to (3.6 ± 0.8) × 10^?4 sec^?1 at 45°C. The dissociation quotient, [II] [NO₃^?]/[Co(NH₃)₅NO₃²⁺], was found to be equal to 0.28 ± 0.11 M at 45°C by NMR methods. The pseudo first-order rate constants for anation of II by NO₃^? and the solvation of Co(NH₃)₅NO₃ ²⁺ by DMSO were determined at various temperatures.     

Transfer chemical potentials for cobalt(III) and chromium(III) complexes from water into aqueous methanol; their relevance to reactivity trends for cobalt(III)-chloride aquation

Summary We report solubilities of a number of cobalt(III) and chromium(III) complex salts in methanol-water mixtures. From these, and published solubilities of salts of other complexes of these metals, we have calculated transfer chemical potentials from water into aqueous methanol for a variety of cationic and anionic complexes of cobalt(III) and chromium(III), using the assumption _m(Ph₄As⁺) + _m(BPh ₄ ^– ). The established trends are discussed in terms of electrostatic factors and of the hydrophilicity or hydrophobicity of the ligands present. The effects of single ion assumptions on conclusions of initial state-transition state analyses of solvent effects on reactivity are assessed with particular reference to aquation of thetrans-[Co(en)₂Cl₂]⁺ andtrans-[Co(py)₄Cl₂]⁺ cations.On leave from the Faculty of Science, Sohag, Egypt.     

Cyclophosphates as ligands for cobalt(III) in water

Examination of cyclotriphosphate and cyclotetraphosphate as ligands for Co(III) in aqueous solutions revealed that cyclotetraphosphate affords stable complexes as a hemilabile ligand, while cyclotriphosphate exhibits facile hydrolysis.     

Kinetics of the solvolysis of thetrans-dichlorobis(1,2-diaminoethane) cobalt(III) in water + ethanonitrile mixtures

Summary The kinetics of the solvolysis of thetrans-[Coen₂Cl₂]⁺ cation (en = 1,2-diaminoethane) have been investigated over a range of temperatures in water with added ethanonitrile which has much less effect on the solvent structure than the acohols already used as co-solvents with water for this solvolysis. However, the non-linear relationship obtained for the variation of log (rate constant) with the reciprocal of the dielectric constant at constant temperature shows that the effect of changing solvent structure is still important, although, as expected from the absence of pronounced extrema in the variation with composition in water + ethanonitrile of physical properties which are influenced by such changes in solvent structure, the enthalpy and entropy of activation for the solvolysis vary smoothly with composition. The application of a free energy cycle shows that changes in solvent structure affect the pentacoordinated cobalt(III) ion in the transition state more than the hexacoordinated cobalt(III) ion in the initial state.     

Photocleavage of lysozyme by cobalt(III) complexes

Photochemical reagents that cleave proteins at specific sites (photoproteases) are useful for studying protein structure and protein-ligand interactions. PolyammineCo(III) complexes are tested here as photochemical probes to cleave proteins. Irradiation of a mixture of lysozyme, a model protein, and polyammineCo(III) complexes resulted in the facile cleavage of the peptide backbone. Photocleavage yielded two fragments of molecular weights 10.6 and 3.7 kDa, and these masses sum to the molecular mass of lysozyme (14.3 kDa). No cleavage was detected in the absence of the metal complex, in the dark, or upon irradiation at wavelengths of >420 nm. The photocleavage yield increased with irradiation time and with the concentrations of the metal complex and the protein. N-terminal sequencing of the 10.6 kDa fragment indicated residues that are identical to the N-terminus of lysozyme, and sequencing of the 3.7 kDa fragment indicated Val-Ala-Trp-Arg, an internal sequence of lysozyme. From the known primary sequence of lysozyme and the sequencing data, the cleavage site was assigned to Trp108-Val109. Molecular modeling indicates that the observed cleavage site is within few angstroms from the proposed metal binding site at Glu35-Asp52. This is the first report of the successful photocleavage of proteins, with high selectivity, by transition metal complexes. This novel observation can facilitate the rational design of transition metal complexes for the photochemical footprinting of metal binding sites on proteins.     

Bacterial activity of cobalt(III) complexes. Part IV: Diethylenetriaminemonoacetatocobalt(III) complexes

Summary The activities of the diethylenetriaminemonoacetatocobalt(III) complexes, [Co(en)(DTMA)]I₂, [CoX₂(DTMA)] and [CoCO₃(DTMA)]·H₂O (DTMA=diethylenetriaminemonoacetato or formally 3-amino-3, 6-diazaoctanato; en=ethylenediamine, X=Cl^–, NO ₂ ^– , NCS^–) were studied onEscherichia coli B growing in a minimal glucose medium in both lag- and log-phases. Activities decrease in the order: [Co(NCS)₂(DTMA)]> [Co(NO₂)₂(DTMA)]>[Co(en)(DTMA)]I₂>[CoCl₂(DTMA)] >[CoCO₃(DTMA)]·H₂O. The antagonistic activities of the complexes were also studied.     

Simple and mixed complexes of cobalt(II) and cobalt(III) ions

Summary Bivalent and trivalent cobalt complexes with 1-(2-pyridylazo)-2-naphthol (PAN), PAN+1, 10-phenanthroline and PAN+2, 2-bipyridyl were prepared and characterized by physico-chemical and magnetic measurements. The spectral studies suggest that PAN behaves as a bidentate ligand and is coordinated to metal ions through oxygen and (pyridine) nitrogen, whereas 1, 10-phenanthroline and 2, 2-bipyridyl are coordinated through (pyridine) nitrogen. The tentative (M–O) and (M–N) band assignments in the lower i.r. region, and magnetic moment data favour four coordination for the complexes studied.     

Cleavage by halogens of carbon—cobalt bonds in organometallic complexes of cobalt(III) : III. Kinetics and mechanism of the reactions of organobis(dimethylglyoximato)cobalt(III) complexes with iodine in chloroform

The kinetics of the reaction between organocobaloximes, RCo(DH)₂H₂O, and iodine have been investigated. They reveal the participation of an RCo(DH)₂H₂O · I₂ intermediate which undergoes intramolecular transalkylation and acts as an electrophile towards a second organocobaloxime molecule. The trend in reactivity as the R group is varied is discussed.     

Polythermal solubility of chromium(III) and cobalt(III) tris(acetylacetonates) in water-tert-butanol mixtures

Solubility data for chromium(III) and cobalt(III) tris(acetylacetonates) in water and water-tert-butanol mixtures over a wide range of temperatures and alcohol concentrations were obtained, and thermodynamic parameters of solution were calculated. The dependences of solubility on the concentration of tert-butanol have an inversion point corresponding to a change in the hydration mechanism, when the solvent structure changes from water to aqueous alcohol.