Solubility of Litharge (α-PbO) in Alkaline Media at Elevated Temperatures

An inert, flowing autoclave facility was used to investigate the solubility behavior of α-PbO (litharge, tetragonal) in aqueous solutions of morpholine, ammonia and sodium hydroxide between 38 and 260 ^∘C. Lead solubilities increased from about 0.4 mmol-kg⁻¹ at 38 ^∘C to about 4.5 mmol-kg⁻¹ at 260 ^∘C and were relatively insensitive to the concentration and identity of the reagent used to control the pH. The measured lead solubilities were interpreted using a Pb(II) ion hydroxocomplexing model and thermodynamic functions for these equilibria were obtained from a least-squares analysis of the data. A consistent set of thermodynamic properties for the species Pb(OH)⁺, Pb(OH)₂(aq) and Pb(OH)₃⁻ was obtained that will permit accurate lead oxide solubility calculations to be made over broad ranges of temperature and alkalinity.     

Synthesis,spectroscopy, electrochemistry,and methylation reaction of the dithiolate-based cobalt(II) complex derived from tert-butyl N-(2-mercaptoethyl)carbamate

A dithiolate-containing a carbamate mononuclear cobalt(II) complex namely, [Co(Boc-S)₂] (1), was obtained by the reaction of a methanolic solution of cobalt(II) nitrate hexahydrate with two equimolar amounts of the deprotonated form of tert-butyl N-(2-mercaptoethyl)carbamate (Boc-SH). The cobalt(II) complex (1) was characterized in the solid state and in solution by using FT–IR, Raman, UV–visible, and EI–mass spectroscopies, as well as thermal and X-ray diffraction studies. Spectral data showed that the carbamate (Boc-SH) acts as a mono-anionic bidentate ligand coordinating the cobalt(II) ion through two imine nitrogen and two deprotonated thiolate sulfur donor atoms in a distorted tetrahedral geometry. The thermoanalytical data evidence that the complex is stable up to 165 °C and undergoes complete decomposition, resulting in CoO. TEM imaging of the oxide residue shows its nano size clusters, suggesting that the complex (1) may be used as a precursor for nano-oxides. X-ray powder diffraction patterns evidence an isomorphism among the complex. The redox behavior of the cobalt(II) complex was also investigated by cyclic voltammetry. The reaction of the dithiolate cobalt(II) complex (1) with methyl iodide appears to occur intramolecularly with the cobalt-bound dithiolate, forming the cobalt(II)-bound dithioether complex [Co(Boc–SCH₃)₂]I₂ (2), as a dication complex with a clean second-order reaction of 13.24 × 10⁻² M⁻¹·s⁻¹.     

Spectrophotometric study of thiocyanato complexation of cobalt(II) and nickel(II) ions in micellar solutions of a nonionic surfactant triton X-100

Complexation of cobalt(II) and nickel(II) with thiocyanate ions has been studied by precise spectrophotometry in aqueous and micellar solutions of a nonionic surfactant Triton X-100 of varying concentrations (20–100 mmol-dm^–3). With regard to cobalt(II), the formation of [Co(NCS)]⁺, [Co(NCS)₂], and [Co(NCS)₄]^2– was established. The formation constant of [Co(NCS)₄]^2–, is increased with increasing concentration of the surfactant, suggesting that the [Co(NCS)₄]^2– complex is formed in micelles. In contrast, the formation constants of [Co(NCS)]⁺ and [Co(NCS)₂] are remained practically unchanged. On the other hand, with nickel(II), the formation of sole [Ni(NCS)]⁺ and [Ni(NCS)₂] was established in both aqueous and micellar solutions examined, their formation constants being also remained unchanged. Interestingly, no higher complex was confirmed in the nickel(II) system, unlike cobalt(II). The unusual affinity of the [Co(NCS)₄]^2– complex with micelles will be discussed from thermodynamic and structural points of view.     

Synthesis,characterization, and electrochemical studies of Co(II,III) dithiocarbamate complexes

Cobalt(II) complexes of N-methyl phenyl, 1-phenylpiperazyl, and morpholinyl dithiocarbamates have been synthesized and characterized by UV–Visible, FTIR, ¹H-, ¹³C-NMR, and mass spectrometry. The spectroscopic data indicated that two ligands coordinated in bidentate chelating to the metal ion to form four-coordinate cobalt(II) complexes (1–3), which was confirmed by mass analysis (TOF MS ES⁺) of the complexes with m/z [M]⁺ = 450.98, 382.94, and 382.94 for 1, 2, and 3, respectively. Single crystal analysis of 2A and 3A show centrosymmetric mononuclear cobalt(III) bonded to three dithiocarbamate ligands forming a distorted octahedral geometry, indicating the cobalt(II) undergoes aerial oxidation to cobalt(III) during recrystallization. In addition, 2A crystallized with one solvated molecule of toluene. The redox behaviors of the complexes were studied by cyclic and square wave voltammetry in dichloromethane; the result revealed a metal centered redox process consisting of a one-electron quasi-reversible process assigned to Co(III)/Co(IV) oxidation and a corresponding Co(IV)/Co(III) reduction. Randles–Sevcik plots (anodic peak current versus the square root of the scan rate (I_p,a versus ν^1/2)) for the redox couples revealed diffusion-controlled behavior.     

Separation of cobalt(II) from nickel(II) by solid-phase extraction into Aliquat 336 chloride immobilized in poly(vinyl chloride)

A solid-phase absorbent obtained by the immobilization of Aliquat 336 chloride in poly(vinyl chloride) is reported to extract preferentially Co(II) from its 7 M hydrochloric acid solutions containing Ni(II). Under the experimental conditions there was no extraction of Ni(II) which allowed the complete separation of these two ions. Co(II) was rapidly and quantitatively back-extracted with deionised water. A mechanism for the extraction of Co(II) is proposed based on the formation of the ion-pair A⁺[HCoCl₄]⁻ where A⁺ is the Aliquat 336 cation. Fe(III) and Cd(II), usually present in Co(II) and Ni(II) samples, were also extracted into the solid-phase absorbent though at a slower rate than Co(II) and they did not interfere with the separation of Co(II) from Ni(II). It was also demonstrated that this approach allowed the complete separation of Ni(II) from the other metal ions mentioned above.     

Investigation of the interaction between cobalt sulfide coatings and Ag(I) ions using cyclic voltammetry in KClO4 and NaOH aqueous solutions and X-ray photoelectron spectroscopy

Cobalt sulfide coatings have been investigated by means of cyclic voltammetry in 0.1 M KClO₄ and 0.1 M NaOH solutions and analyzed using X-ray photoelectron spectroscopy. They have been shown to contain CoS(OH), CoS and Co(OH)₂. After treating such Co sulfide coatings with AgNO₃ solution, their composition changes: both the cobalt and oxygen content decreases and Ag (up to 85 at%) appears in the coating as Ag₂S, Ag₂O and metallic Ag. Co(II) compounds react with Ag⁺ ions according to an exchange reaction [CoS+2Ag⁺+2H₂O→Ag₂S+Co(OH)₂+2H⁺]. In the course of the reaction of Co(OH)₂ with silver ions, a redox process occurs, giving metallic silver [Co(OH)₂+Ag⁺+H₂O→Ag°+Co(OH)₃+H⁺ or Co(OH)₂+Ag⁺→Ag°+CoO(OH)+H⁺]. Ag₂S reduction takes place at more positive potentials than Cu reduction; therefore sulfide layers of cobalt modified with silver ions, unlike unmodified ones, may be plated with Cu from both acid and alkaline electrolytes. Electronic Publication     

Cobalt(II) Chloride Complex Formation in Acetamide–Calcium Nitrate Tetrahydrate Melts

The absorption spectra of Co(II) chloride complexes, containing variable concentrations of chloride ligand, in a molten mixture of 80 mol% acetamide–20 mol% calcium nitrate tetrahydrate, were studied at 313, 333, 353, and 363 K, in the wavelength range 400-800 nm. The melt contains three possible ligands (CH₃CONH₂, H₂O, and NO₃ ^-) for competition with added chloride ligand. Addition of chloride caused a shift of the absorption maximum of octahedral cobalt(II) nitrate towards lower energies and pronounced changes in the shape of the initial spectrum of cobalt(II) nitrate. The effect of temperature changes on the molar absorption coefficient of the Co(II) species was dependent on the chloride concentration and was attributed to the structural changes occurring in the cobalt(II) species. The STAR and STAR FA programs were applied to identify the complex ionic species and to calculate the stability constants of Co(II) complexes formed in this solvent. The results indicate the highest probability of formation of the following complex species: Co(NO₃)₄ ^2-, Co(NO₃)₂Cl₂ ^2-, and CoCl₄ ^2-. Stability constants of each complex were presented for the equilibria occurring at 313, 333, 353, and 363 K. Distribution of the Co(II) species was also calculated over the ranges of chloride concentration and temperature investigated.     

Solubility and phase behavior of nickel oxide in aqueous sodium phosphate solutions at elevated temperatures

A platinum-lined, flowing autoclave facility was used to investigate the solubility/phase behavior of nickel oxide (NiO) in aqueous sodium phosphate solutions between 290 and 560 K. A layer of hydrous nickel oxide was concluded to exist on the nickel oxide surface below 468 K; only at higher temperatures did the anhydrous nickel oxide phase control the nickel ion solubility behavior. The measured solubility behavior was examined via a nickel(II) ion hydrolysis/complexing model and thermodynamic functions for the hydrolysis/complexing reaction equilibria were obtained from a least-squares analysis of the data. The existence of two new nickel ion complexes are reported for the first time: Ni(OH)₂(HPO₄)⁼ and Ni(OH)₃(H₂PO₄)⁼. The positive entropy change associated with the formation of Ni(OH)₃(H₂PO₄)⁼ leads to its dominance in alkaline phosphate solutions at elevated temperatures.     

Conductance behavior of some tris(ethylenediamine)cobalt(III) complexes and their ion association in aqueous solutions

The conductance behavior of some tris(ethylenediamine)cobalt(III) complexes was studied in dilute aqueous solutions at 25°C to investigate the ion-pair formation. The thermodynamic formation constants of the ion pairs [Co(en)₃]³⁺·X^– are 28 (chloride), 28 (bromide), 19 (nitrate), and 15 (perchlorate). These values were compared with theoretical values calculated by using Bjerrum's theory of ion association. The formation constant of [Co(en)₃]³⁺·Cl^– was larger than that obtained from the spectrophotometric measurement in solutions containing perchlorate ion. This difference in the formation constants was explained by considering the contribution of ion association of the complex cation with perchlorate ion.     

Thermal Analysis of Cobalt(II) Salts with some Carboxylic Acids

The thermal analysis of CoC₂O₄·2H₂O, Co(HCOO)₂·2H₂O and Co(CH₃COO)₂·4H₂O was carried out with simultaneous TG-DTG-DTA measurements under non-isothermal conditions in air and argon atmospheres. The intermediates and the end products of decomposition were characterised by X-ray diffraction and IR and UV-VIS spectroscopy. The decomposition of the studied compounds occur in several stages. The first stage of dissociation of each compound is dehydration both in air and argon. The next stages differ in air and argon. The final product of the decomposition of each compound in air is Co₃O₄. In argon it is a mixture of Co and CoO for cobalt(II) oxalate and cobalt(II) formate but CoO for cobalt(II) acetate. This revised version was published online in August 2006 with corrections to the Cover Date.     

Complexation between nickel(II), cobalt(III) and hydrazones derived from pyridoxal 5′-phosphate and hydrazides of 2-,3-,4-pyridinecarboxylic acids in aqueous solution

abstract

The present work reports on stoichiometry, apparent stability constants of biologically relevant complexes of nickel(II), cobalt(III) with hydrazones derived from pyridoxal 5′-phosphate and hydrazides of 2-,3-,4-pyridinecarboxylic acids at pH 7.4, T?=?25.0?°C, I?=?0.25 determined using UV-Vis spectroscopy. The thermodynamic constants of some complexes formation (NiL, NiL₂, NiL₂H) were estimated. Cobalt(II) ion was found to be oxidized to cobalt(III). Co(II) and Co(III) form low-spin state complexes. Hydrazones binding ability (pL_0.5) in the medium mimicking biological ones towards Ni(II) and Co(III) was estimated.     

Syntheses,Characterization and Equilibrium between Mono—and Aqua—bridged Dicobalt（Ⅱ）Complexes.A Structural Model for Methionine Aminopeptidase

A monomeric complex [Co(Im)₂(O₂CMe)2] (1) and a novel aquabridged dimeric complex [Co₂(μ‐H₂O)(μ‐CMe)₂(Im)₄‐(O₂CMe)₂] (2) (Im = imidazole) have been synthesized and characterized. Complexes 1 and 2 coexisted in solution. Pure forms of either complex can be obtained from the same solution by controlling the crystallization conditions. All two complexes possess a carboxylate‐Im‐cobalt(II) triad system analogous to the carboxylate‐histidine‐metal triad systems that have been found in many zinc enzymes and cobalt(II)‐substituted enzymes. In 2, two Co²⁺ ions are connected by a water molecule in a bridging fashion with Co°Co [0.3687(1) nm], Co—OH₂ [0.2159(3) nm], and Co‐OH₂‐Co [117.2(3)°], in which the water molecule is further stabilized by two intramolecular hydrogen bonds with the oxygens of the terminal monodentate acetate groups with the distance of O…0 [0.2609(7) nm]. The terminal monodentate acetate groups display quite abnormal geometry due to the strong “pulling effect” on the carboxylates by intermolecular and intramolecular hydrogen bonds. Complex 2 showed weak antiferromagnetic coupling at low temperature with g = 2.22 and J = ?1.60 cm^?1.     

配合物[Co(qina)2(DMSO)2]的结构及其对乙酸-1-萘酯水解的催化研究

合成了配合物[Co(qina)₂(DMSO)₂]单晶, 其中, qina^－为喹哪啶酸根, DMSO为二甲基亚砜. 配合物为单斜晶系, P2(1)/C空间群, 2个qina^－配体以氮原子和氧原子与Co(II)离子螯合配位, 2个DMSO以氧原子与Co(II)离子轴向配位, 形成规则的八面体构型配合物, 分子之间存在π-π堆积弱相互作用. 该配合物可显著提高乙酸-1-萘酯的水解速率, 在配合物浓度和萘酯浓度各为1.0×10^－4和3.0×10^－5 mol•L^－1条件下, 酯的水解速率提高460倍.     

Water-Assisted Concerted Proton-Electron Transfer at Co(II)-Aquo Sites in Polyoxotungstates With Photogenerated RuIII(bpy)33+ Oxidant

The cobalt substituted polyoxotungstate [Co₆(H₂O)₂(α-B-PW₉O₃₄)₂(PW₆O₂₆)]¹⁷⁻ ( Co6 ) displays fast electron transfer (ET) kinetics to photogenerated Ru^III(bpy)₃³⁺, 4 to 5 orders of magnitude faster than the corresponding ET observed for cobalt oxide nanoparticles. Mechanistic evidence has been acquired indicating that: (i) the one-electron oxidation of Co6 involves Co(II) aquo or Co(II) hydroxo groups (abbreviated as Co6(II) −OH ₂ and Co6(II) −OH, respectively, whose speciation in aqueous solution is associated to a pK_a of 7.6), and generates a Co(III)−OH moiety ( Co6(III) −OH), as proven by transient absorption spectroscopy; (ii) at pH>pK_a, the Co6(II) −OH→Ru^III(bpy)₃³⁺ ET occurs via bimolecular kinetics, with a rate constant k close to the diffusion limit and dependent on the ionic strength of the medium, consistent with reaction between charged species; (iii) at pH <pK_a, the process involves Co6(II) − OH₂ → Co6(III)−OH transformation and proceeds via a multiple-site, concerted proton electron transfer (CPET) where water assists the transfer of the proton, as proven by the absence of effect of buffer base concentrations on the rate of the ET and by a H/D kinetic isotope in a range of 1.2–1.4. The reactivity of water is ascribed to its organization on the surface of the polyanionic scaffold through hydrogen bond networking involving the Co(II)−OH₂ group.     

Synthesis,X-ray crystal structure and DFT studies of cobalt(II) and vanadium(V) complexes with N,N,O-tridentate aroyl-hydrazone based ligand

A new aroyl-hydrazone, 2-pyridine carboxaldehyde-derived hydrazone ligand and its cobalt(II) (1) and vanadium(V) (2) complexes were prepared. The structures of these compounds were investigated using elemental analysis, spectral (IR, UV), and X-ray diffraction measurements. The electrochemical properties of the complexes were studied by cyclic voltammetry. The hydrazone ligand acted as tridentate and coordinated to vanadium and cobalt via N-imine, N-pyridine, and O-benzohydrazide atoms. The Co(II) complex crystallizes in the monoclinic system, space group P2₁/c, and has a binuclear structure. Chloride ions behave as the linking bridge and a tridentate hydrazine ligand HL and water as the terminal capping ligands. The central Co(II) ion has distorted octahedral geometry. The vanadium(V) complex crystallizes in the monoclinic crystal system, space group P2₁/n, and can be described as having highly distorted trigonal-bipyramidal coordination. The geometries and electronic properties of the complexes were also obtained using DFT and TD-DFT calculations.     

Crystal structures of cobalt(II) complexes with N-(2-hydroxyethyl)iminodiacetic and N,N-bis(2-carbamoylethyl)aminoacetic acids: Co(Heida)·2H2O and Co(Bcegly)(ClO4)·2H2O

The cobalt atom in the structures studied is situated in the center of an octahedron involving donor atoms N and 3O organic ligands Heida or Bcegly (ions of hydroxyethyliminodiacetate or bis(carbamoylethyl)aminoacetate, respectively), water molecule oxygen atom, and a carboxylic atom of the neighboring ligand in the trans-position to the N atom, so that each (II) ion is linked with two organic anions. This results in a formation of infinite chains — uncharged [Co(Heida)(H₂O)]_n or cationic {[Co(Bcegly)(H₂O)]⁺}_n. In both cases, a molecule of crystallization water is present, and in the second case, the charge of the chains is compensated by perchlorate ions. Aminoacetic cycle of the Heida ligand is approximately coplanar to another such cycle, while a similar cycle of the Bcegly ligand is in the plane of one of six-membered aminopropionamide cycles.     

Synthesis,structures, and characterization of copper(II), nickel(II), and cobalt(III) metal complexes derived from an asymmetric bidentate Schiff-base ligand

An asymmetric bidentate Schiff-base ligand (2-hydroxybenzyl-2-furylmethyl)imine (L–OH) was prepared. Three complexes derived from L–OH were synthesized by treating an ethanolic solution of the appropriate ligand with an equimolar amount of metallic salt. Three complexes, Cu₂(L–O^?)₂Cl₂ (1), Ni(L–O^?)₂ (2) and Co(L–O^?)₃ (3), have been structurally characterized through elemental analysis, IR, UV spectra and thermogravimetric analysis. Single crystal X-ray diffraction shows metal ions and ligands reacted with different proportions 1?:?1, 1?:?2 and 1?:?3, respectively, so copper(II), nickel(II), and cobalt(III) have different geometries.     

Synthesis,crystal structures,DNA binding and cleavage properties and protein binding activities of three mononuclear cobalt(II) complexes

Three new mononuclear cobalt(II) complexes containing ligands with extended planar quinoxaline moieties, {dipyrido[3,2‐a:2′,3′‐c]phenazine (dppz) or dipyrido[3,2‐d:2′,3′‐f]quinoxaline (dpq)}, viz. [Co(dppz)(acac)₂] · CH₃OH ( 1 ), [Co(dpq)(tfnb)₂] ( 2 ) and [Co(dpq)(dbm)₂] ( 3 ), where acac = acetylacetonate, tfnb = benzoyltrifluoroacetone and dbm = dibenzoylmethane, have been synthesized and structurally characterized as octahedral complexes. The binding ability of the complexes with calf thymus (CT)‐DNA has been investigated by spectroscopic and viscosity measurements. Results indicate that all complexes bind to CT‐DNA via intercalative mode, and the DNA binding affinity of dppz complex 1 is apparently stronger than that of dpq complexes 2 and 3 . Furthermore, DNA photocleavage experiments indicate that these complexes are efficient DNA cleaving agents in UV‐A (365 nm) and hydroxyl radical (HO^·), singlet oxygen (¹O₂) and superoxide anion (¹O₂^?) serve as the major cleavage active species. In addition, interaction of the complexes with bovine serum albumin (BSA) was investigated using UV ? visible and fluorescence methods, which indicated that all complexes could quench the intrinsic fluorescence of BSA in a static quenching process. Copyright © 2014 John Wiley & Sons, Ltd.     

Characteristic features of the synthesis, solubility products, and absorption spectra of basic cobalt(II) acetate, nitrate, and chloride salts

The solubility products of basic cobalt(II) salts Co(OH)_1.80(An)_0.20, where An are NO₃⁻ and CH₃COO⁻, and Co(OH)_1.50(CH₃COO)_0.50 were determined by the method of three variables. The stability of the salts Co(OH)_1.80(An)_0.20 against hydrolysis increases in the series < CH₃COO⁻ < Cl⁻. The absorption maxima of Co²⁺ ions in solutions, β-Co(OH)₂ powders, and the pink Co(OH)_1.50Cl_0.5 salt are located in the frequency regions typical of the octahedral coordination; those of CoOH⁺ ions in solutions and powders of green basic cobalt salts are in the frequency regions typical of the tetrahedral coordination. A model for the formation and interconversion of basic cobalt salts with single-charged anions is proposed.     

Benzo[h]quinoline based Macrocyclic Copper(II), Cobalt(II) Complexes: Synthesis,Characterization and Light induced DNA Cleavage Studies

A new ligand dibenzo[h]quinolineno[1,3,7,9] tetraazacyclododecine-7,15 (14H, 16H)-dibenzene (L) and its Co(II)/Cu(II) metal complexes of type [MLX₂] (Where (M = Co(II) (5), Cu(II) (6) and X = Cl) were synthesized and are well characterized by FT-IR, ¹H-NMR, FAB mass elemental analysis, and electronic spectral data. The role of the cobalt/copper metals in photo-induced DNA cleavage reactions was explored by designing complex molecules having macrocyclic structure. Finally, we have shown that photocleavage of plasmid DNA is more efficiently enhanced when this macrocyclic ligand is irradiated in the presence of copper(II) than that of cobalt metal.