Cobalt Complex Ions Research Articles

Magnetic anisotropy and slow relaxation of magnetisation in double salts containing four- and six-coordinate cobalt(II) complex ions.

Four novel Co(II) coordination compounds 1-4 of the general formula [Co(Ln)2][Co(NCY)4]·mCH3CN (where Ln are tridentate ligands L1 = 2,6-bis(1-hexyl-1H-benzimidazol-2-yl)pyridine for 1 and 2; L2 = 2,6-bis(1-octyl-1H-benzimidazol-2-yl)pyridine for 3; L3 = 2,6-bis(1-dodecyl-1H-benzimidazol-2-yl)pyridine for 4, Y = O for 1, 3, and 4 and Y = S for 2; m = 0 for 1 and 3, m = 0.5 for 2 and m = 2 for 4) were prepared and characterised. The molecular structures of all four compounds consist of the hexacoordinate complex cation [Co(Ln)2]2+ and tetracoordinate complex anion [Co(NCY)4]2-, with distorted octahedral and tetrahedral symmetry of coordination polyhedra, respectively. The electronic structures of all compounds feature an orbitally non-degenerate ground state well-separated from the lowest excited state, which allows the analysis of the magnetic anisotropy by the spin Hamiltonian model. ZFS parameters, derived from both CASSCF-NEVPT2 calculations and magnetic data analysis, indicate that tetrahedral anions [Co(NCY)4]2- exhibit small axial parameters |D| spanning the range of 2.2 to 7.7 cm-1, while octahedral cations [Co(Ln)2]2+ display significantly larger |D| parameters in the range of 37 to 95 cm-1. For 1-3, the Fourier-transform infrared magnetic spectroscopy (FIRMS) revealed a reasonable transmission with a magnetic absorption around the expected value for the ZFS accompanied by features allowing to identify phonon frequencies and simulate spin-phonon couplings. Dynamic magnetic investigations unveiled the field-induced slow relaxation of magnetisation, with maximal relaxation times (τ) of 92(2) μs for 2 at 2 K and BDC = 0.3 T. The temperature evolution of τ was analysed using a combination of Orbach, direct and Raman relaxations (Ueff = 8(1) K (5.6 cm-1)) or Orbach, direct and spin-phonon induced relaxations (Ueff = 10.3(9) K (7.2 cm-1)). The rest of the complexes, namely 1, 3, and 4 show field-induced slow relaxation of magnetisation with τ smaller than 16 μs.

Bis(N,N-diethyl-4-methyl-4-piperazine-1-carboxamide) tetra-kis-(iso-thio-cyanato-κN)-cobalt(II), a model compound for the blue color developed in the Scott test.

The complex, bis-(N,N-diethyl-4-methyl-4-piperazine-1-carboxamide) tetra-kis(iso-thio-cyanato-κN)cobalt(II) (N,N-diethyl-4-methyl-4-piperazine-1-carboxamide = di-ethyl-carbamazine), (C10H22N3O)2[Co(NCS)4], is presented. This com-plex is a blue precipitate, insoluble in water but soluble in organic solvents, that is formed from the reaction of diethylcarbamazine citrate, a protonated tertiary amine, with cobalt(II) and thio-cyanate. This reaction, in the form of the Scott test, is a common presumptive test for cocaine hydro-chloride. The known cobalt compound, [K2Co(NCS)4]·3H2O, has a deep-blue coloration due to the tetra-hedral [Co(NCS)4]2- that is also present in the ion pair with bulky amines, and is similar to the color of other tetra-hedral cobalt(II) complex ions, such as [CoCl4]2-. The structure is consistent with a previous proposal that a hydro-phobic ion pair formed between [Co(NCS)4]2- and two protonated mol-ecules of cocaine is responsible for the blue hydro-phobic products formed by cocaine in the Scott test.

Electron Transfer Reaction of Tris(1,10-phenanthroline)cobalt(III) Complex and Iodide Ion in An Aqueous Acidic Medium

The kinetics and mechanistic study of the electron transfer of tris(1,10-phenanthroline)cobalt(III) complex and iodide ion has been carried out in an aqueous acidic medium at ionic strength(I) = 0.20 mol dm−3 (NaCl), [H+] = 0.02 mol dm−3, T = 28 ± 1.0 °C and λmax of 495 nm. The rate of reaction was found to be third order overall: first order in the oxidant and second order in the reductant, and acid independent. The empirical rate law conforms to the equation: $$- = {\text{ k}}[({\text{Co}}\left( {{\text{phen}}} \right)_{{3}} )^{{{3} + }} ]\left[ {{\text{I}}^{ - } } \right]^{{2}}$$ The reaction rate was unaffected by change in ionic strength and dielectric constant of the reaction medium. Added cations and anions catalysed and inhibited the reaction rate respectively. Based on spectroscopic investigation and kinetic pieces of evidence from the Michaelis–Menten plot and effect of added ions, an outer sphere mechanism has been rationalised for the reaction.

Wide wavelength photon harvesting in dye-sensitized solar cells utilizing cobalt complex redox electrolyte: Implication of surface passivation

A combination of near infra-red (NIR) photon harvesting and cobalt electrolytes having deeper redox energy level are needed for the fabrication of high efficiency dye-sensitized solar cells (DSSCs). A logical molecular design of unsymmetrical squaraine dye (SQ-110) as a representative of NIR dyes has been demonstrated to function well in DSSC using cobalt complex redox electrolyte. Problem of mass transport limitations due to the bulky cobalt complex ions leading to relatively enhanced charge recombination was amicably solved by single as well as multiple compact metal oxide surface passivation on both of the transparent conducting oxide substrate as well as mesoporous TiO2. Complete absence of light absorption beyond 550 nm wavelength region by D-35 and utilization of a complementary light harvesting dye SQ-110 led to efficient wide wavelength photon harvesting. DSSC fabricated using a dye cocktail of D-35 and SQ-110 in 4:1 ratio resulted in to photoconversion efficiency (PCE) of 7.2%, which is much higher as compared to the constituent individual sensitizers D-35 (3.6%) and SQ-110 (1.9%). This synergistic enhancement in PCE by dye cocktail was associated with the mutual co-operation of respective dyes in terms controlling the dye aggregation and complementary photon harvesting. In this dye cocktail system, D-35 is involved in the prevention of dye aggregation, lower wavelength photon harvesting and energy transfer induced photocurrent enhancement.

Kinetic studies of gold leaching from a gold concentrate calcine by thiosulfate with cobalt-ammonia catalysis and gold recovery by resin adsorption from its pregnant solution

The leaching of gold from a gold concentrate calcine using a novel thiosulfate leaching method that utilizes cobalt-ammonia complex as the oxidant in place of the traditional copper-ammonia catalysis was investigated. The result shows that the thiosulfate consumption can be evidently reduced without the impact on the gold extraction. The leaching kinetics of gold in thiosulfate solution with cobalt-ammonia catalysis has been studied. It was found that the reaction orders with respect to ammonia, cobalt and thiosulfate concentrations are 0.42, 0.20 and 0.34, respectively. The optimal pH value for gold leaching is 10.0, and gold can be effectively extracted at ambient temperature. The apparent activation energy is determined to be 5.68 kJ/mol, and this indicates that the gold leaching in the Co-NH3-S2O32− system is likely to be controlled by the diffusion of reactants and products through a solid layer. The XPS analysis results strongly support this hypothesis. The apparent activation energies of gold leaching in the thiosulfate-only and Cu-NH3-S2O32− systems are 30.9 kJ/mol and 8.01 kJ/mol, respectively. It can be concluded that the cobalt-ammonia catalysis for thiosulfate leaching of gold has higher catalytic efficiency than copper-ammonia catalysis. The tests for gold recovery from the pregnant solution of the Co-NH3-S2O32− system by resin adsorption were implemented, and the results demonstrated that the competitive adsorption of cobalt with gold did not occur owing to the weak affinity of the strong base anion resin for cobalt complex ions. Therefore, the elution of gold on loaded resin only needs to perform a simple one-stage process instead of the complex two-stage elution process for the Cu-NH3-S2O32− system, which will be contribute to reduce the cost of gold recovery from the pregnant solution.

A comparative study on the electron transfer reaction (ETR) of surfactant cobalt(iii) complexes of aliphatic/aromatic ligands in micro heterogeneous media: a thermodynamic approach

The electron transfer reaction between different surfactant cobalt(iii) complex ions and Fe2+ ions in micelles as well as β-cyclodextrin was studied at different temperatures using a spectrophotometry method.

Computational analysis of tris(1,2-ethanediamine) cobalt(III) complex ion: calculation of the 59Co shielding tensor using LF-DFT

The ligand-field density functional theory (LF-DFT) approach is employed for calculations of the 59Co nuclear magnetic resonance (NMR) shielding tensor of all four diastereoisomers (λλλ, λλδ, λδδ, and δδδ) of tris(1,2-ethanediamine) cobalt(III) complex ion, [Co(en)3]3+. The obtained values split into two groups according to the point group of the diastereoisomers. The influence of the individual ring conformation on the 59Co NMR shielding tensor is small. Comparisons with results obtained with conventional DFT and experimental values are given. The good agreement between calculated and experimental values demonstrates the validity of LF-DFT for calculating the shielding tensor for transition-metal complexes. .

Synthesis and structural characterization of a novel seven-coordinate cobalt(II) complex: 2,9-Bis(ethanolamine)-1,10-phenanthrolinechlorocobalt(II) chloride

Condensation reaction of 2,9-dicarboxaldehyde-1,10-phenanthroline with 2-aminoethanol followed by NaBH 4 reduction yielded the polydentate Schiff base ligand 2,9-bis(ethanolamine)-1,10-phenanthroline in its reduced form. This ligand was characterized by elemental analysis, LC–MS, IR, UV–Vis and NMR spectroscopy. Reaction of the reduced Schiff base ligand with aqueous solution of cobalt(II) chloride affords 2,9-bis(ethanolamine)-1,10-phenanthrolinechlorocobalt(II) chloride in high yield. Single crystals of the cobalt(II) complex were obtained from the crystallization in ethanol and its structure was elucidated by X-ray structural analysis. The cobalt(II) complex ion was found to be seven-coordinated in a pentagonal bipyramidal geometry, whereby cobalt(II) ion is surrounded by the six donor atoms in the ligand molecule and a chloride ion.

Synthesis, characterization, and electron transfer reaction of some surfactant–cobalt(III) complex ions

The surfactant complex ion cis-[Co(tmd)2(C12H25NH2)2]3+ (tmd = 1,3-propanediamine, C12H25NH2 = dodecylamine) has been synthesized and characterized by elemental analysis and spectral data. In addition we have determined the critical micelle concentration of the surfactant–cobalt(III) complex and studied the kinetics and mechanism of the complex with ferrocyanide anion. The reaction is found to be second order, and the second-order rate constant increases with increasing initial concentration of the surfactant–cobalt(III) complex due to the presence of self-micelles formed by the complex itself. The thermodynamic parameters were determined. The results have been analyzed.

Studies on outer-sphere electron transfer between iron(II) and some surfactant–cobalt(III) complexes in micelles as well as in β-cyclodextrin

The kinetics and mechanism of iron(II) reduction of the surfactant–cobalt(III) complex ions, cis-[Co(bpy) 2(C 12H 25NH 2) 2] 3+, cis-[Co(phen) 2(C 12H 25NH 2) 2] 3+ (bpy = 2,2′ bipyridine, phen = 1,10 phenanthroline, C 12H 25NH 2 = dodecylamine) in self-micelles were studied at different temperatures. Experimentally the reaction was found to be second order and the electron transfer postulated as outer-sphere. The second order rate constant for this electron transfer reaction for both the complex ions was found to increase with increase in the initial concentration of these surfactant–cobalt(III) complex ions. The effect of inclusion of the long aliphatic chain of the surfactant complex ions into β-cyclodextrin on these reactions has also been studied.

Synthesis, micellar properties, DNA binding and antimicrobial studies of some surfactant–cobalt(III) complexes

A new class of surfactant–cobalt(III) complex ions of the type, cis-[Co(X) 2(C 14H 29NH 2)Cl] 2+ (where X = ethylenediamine (en), or 2,2'-bipyridyl (bpy), or 1,10-phenanthroline (phen)) and cis-[Co(trien)(C 14H 29NH 2)Cl] 2+ (trien = triethylenetetramine) were synthesized and characterized by IR, NMR, UV–visible electronic absorption spectra, elemental analysis and metal analysis. The critical micelle concentration (CMC) values of these surfactant–cobalt(III) complexes in aqueous solution were obtained from conductance measurements. Specific conductivity data (at 298, 308, 318 and 328 K) served for the evaluation of the temperature-dependent CMC and the thermodynamics of micellization (Δ G 0 m, Δ H 0 m and Δ S 0 m). Interactions between calf thymus DNA and the surfactant–cobalt(III) complexes in aqueous solution have been investigated by electronic absorption spectroscopy, emission spectroscopy and viscosity measurements. The electrostatic interactions, van der Waals interactions and/or partial intercalative binding have been observed in these systems. The surfactant–cobalt(III) complexes were screened for their antibacterial and antifungal activities against various microorganisms. The results were compared with the standard drugs, Ciprofloxacin and Fluconazole respectively.

Determination of dissociation constants for coordination compounds of Cr(III) and Co(III) using potentiometric and spectrophotometric methods

The acid–base properties of analogous complex ions of chromium(III) and cobalt(III) in aqueous solution have been studied. The equilibrium constants for all metal complexes were determined by using potentiometric and spectrophotometric titration methods. First, dissociation constants for the studied complexes of Cr(III) and Co(III) were determined by means of the potentiometric titration method and using the STOICHIO computer programme. Then, pH-spectrophotometric titrations were performed and the OriginPro 7.5 computer programme was used to calculate the same constants. The measurements using both methods were carried out under the same conditions of temperature, T = 298.15 K, and over the same pH range 2.00–10.00, respectively. It turned out that the two methods used enabled us to obtain acidity constants in very good agreement.

Reactivity of 1,2,4,5-tetracarboxylatebenzene with cobalt(II)

The complexes [Co(H2O)6][Co(BTCA)(H2O)4]⋅7.2H2O (1) and [Na2Co(H2O)4(μ-H2O)2 (μ-BTCA)] (2) (BTCA = 1,2,4,5-tetracarboxylatebenzene) have been synthesized and characterized by single crystal X-ray diffraction. Compound (1) crystallizes in the triclinic space group P-1 with a = 6.8591(9) A, b = 9.9691(13) A, c = 10.9231(11) A, α = 93.021(2)∘, β = 104.883(2)∘, and γ = 103.702∘ with Z = 1. This compound exhibits a 1-dimensional structure of two alternating layers. A chain of cobalt ions and BTCA constitute one layer. Cobalt complex ions and solvent water molecules occupy the other. Compound (2) crystallizes in the monoclinic space group C 2/m with a = 8.8647(6) A, b = 10.5247(7) A, c = 21.2265(14) A, and β = 92.525(2)∘, with Z = 2. This compound consists of a 3-dimensional network of cobalt and sodium ions linked by BTCA. The sodium complex moiety is disordered around a center of inversion.

Cobalt(III) EDTA complex removal from aqueous alkaline borate solutions by nanofiltration

At the PWR Paks diluted low-level radioactive waste water (LLW) contains the long-lived 60Co isotope in EDTA complex form, which has no simple separation procedure. In this research nanofiltration(NF) was studied for selective removal of the cobalt(III) EDTA complex from a drain waste water model solution, which contains mainly sodium borate at an alkaline pH. A suitable NF membrane was chosen to separate the cobalt complex from the borate solution. The NF experiments were performed at constant temperature (25°C) and pressure range 1–10 bar. The cobalt complex and the borate ion rejection ( R) as well as the permeate flux of the membrane was investigated as a function of pH. The rejection of the cobalt(III) EDTA complex ion and especially the borate were strongly pH dependent. The rejection of the complex ion and the borate was increased at alkaline pH (at pH 8, R = 73%; at pH 11.5, R = 96% for the cobalt complex; at pH 8, R = 7%; at pH 11.5, R = 59% for borate). NF seems to be a suitable separation method for the removal of the Co(III) EDTA complex from nuclear power plant waste streams. The removal of the cobalt complex ion from an alkaline borate solution by NF is possible in two ways: at slightly alkaline pH by a two-step separation, or at a more alkaline pH (pH > 9.5) by a one-step separation.

Chiral recognition in association between antimony potassium tartrate and bis(L-alaninate)ethylenediamine cobalt(III) complexes using electrospray ionization mass spectrometry

The chiral recognition of metal complexes by a quick and sensitive mass spectrometric analysis was investigated. The principle is introduction of an external chiral standard compound and detection of the differential association with two optical isomers. Using electrospray ionization mass spectrometry we detected weak intermolecular association between the external chiral anion bis(μ-L-, D-tartrato)-diantimonate(III), [Sb 2(L-, D-tart) 2] 2− and isomeric bis(L-alaninate) ethylenediamine cobalt(III) complex ions, [Co(L-ala) 2(en)] + in acetonitrile/water solution. The difference in the association with optical isomers of the Co complex was measured. The results were interpreted based on a model of intermolecular interaction involving hydrogen bonding. The prospects of the mass spectrometry method for chiral recognition using the external chiral negative ion [Sb 2(L-, D-tart) 2] 2− was discussed.

Effects of Tripositive Cobalt(III)-Complex Ions on the Structure of a Cholesteric Mesophase Composed of PotassiumN-Dodecanoyl-l-alaninate

The phase behavior of the aqueous cholesteric mesophase composed of potassium N-dodecanoyl-l-alaninate (L-KDDA) was studied in the presence of various cations such as a cobalt(III) complex and cesium ions using multinuclear magnetic resonance and laser and X-ray scatterings. The cobalt(III) complexes used are [Co(NH3)6]Cl3, [Co(en)3]Cl3 (en = ethylenediamine), Δ-[Co(chxn)3]Cl3 (chxn = (R,R)-1,2-cyclohexanediamine), [Co(tn)3]Cl3 (tn = trimethylenediamine), and [Co(phen)3]Cl3 (phen = 1,10-phenanthroline). Transition temperatures from anisotropic to isotropic phases determined by 2H2O NMR spectra were appreciably dependent on the kinds and concentrations of the added cations. The NH3-, en-, tn-, and phen-complex ions were more favorable for stabilizing the aqueous mesophase of L-KDDA compared to the chxn-complex ion. The change in the order parameters for the surfactant aggregates was monitored by anisotropic splittings of the 1H NMR spectra envelope and was compared to structural parameters of the mesophase...

Solvent Effects on 59Co Chemical Shifts for Tripositive Cobalt(III) Complex Ions

Abstract Interactions of tripositive cobalt(III) complex ions, such as Δ(lel3)-[Co(chxn)3]3+ (chxn = (R,R)-1,2-cyclohexanediamine), [Co(oct-en)(2,3,2-tet)]3+ (oct-en = N-octylethylenediamine, 2,3,2-tet = 3,7-diazanonane-1,9-diamine), [Co(sep)3]3+ (sep = sepulchrate = 1,3,6,8,10,13,16,19-octaazabicyclo[6.6.6]eicosane), and [Co(tn)3]3+ (tn = trimethylenediamine), in various solvents were studied using 59Co chemical shifts together with the electronic absorption spectra. The results are discussed in comparison with those of [Co(en)3]3+, whose 59Co chemical shift in various solvents had been previously reported to be fairly proportional to the donor numbers. There was a trend that the 59Co chemical shift changes greatly if the acidic NH-hydrogen atoms of the ligands are favorable to form hydrogen bonding with the solvents. The magnitudes of the chemical-shift changes for [Co(tn)3]3+ were significantly smaller than those for the en and chxn complexes. This difference can be attributed to the more conformationally labile structure of the tn complex in solution.

The ion-pair association constant of oxalate with fac-tris(2-aminomethylpyridine)cobalt(III)

The equilibrium constant K for the ion-pair formation fac-[Co(pic) 3] 3+ + C 2 O 2 2− ⇌ fac-[Co(pic) 3] 3+/C 2O 4 2−1 where pic = 2-aminomethylpyridine, has been determined spectrophotometrically at 0.35 M (KCl) ionic strength and 25.0°C, using four different calculation approaches. The best results were obtained when the concentration of the minor component (the cobalt complex ion) was not neglected in comparison with the oxalate ion concentration. The value of K (5.3 M −1) increases when the supporting electrolyte is LiCl (K = 8.2 M −1). The effect of the ionic strength variation from 0.35 to 2.0 M (LiCl) was also investigated.

Ion-pairing effects on the 59Co electric field gradients in the NMR relaxations of tripositive cobalt(III) complex ions

59Co NMR relaxation rates for the [Co(chxn) 3] 3+ (chxn = trans-(1R,2R)-1,2-diaminocyclohexane) and [Co(en) 3] 3+ (en = ethylenediamine) ions were measured in the presence of sulfate or oxalate ions. 1H relaxation rates for the chxn ligands in the same systems were also measured. The ratios of the 59Co relaxation rates to the 1H ones indicate that the 59Co electric field gradient of [Co(chxn) 3] 3+ is appreciably decreased by the formation of the 1:1 ion pair with the sulfate ion. The difference of the concentration dependence of the 59Co NMR relaxations between the sulfate and the oxalate ions can be attributed to the faster change in the configuration of the 1:1 ion pair of the oxalate ion.

Estimation of the Ratio of Hidden Multivalent Ions in Nematic Lyomesophases by Using Heteronuclear NMR

Abstract An estimation of the peak areas of the 59Co NMR spectra for cobalt(III) complex ions and of the 25Mg spectra for magnesium aqua ions gave population ratios of their hidden ions, which are defined as too strongly interacting with nematic lyomesophases (composed of cationic or anionic surfactants) to contribute to the NMR spectra. The cobalt(III) complex ions used were [Co(NH3)6]3+, [Co(en)3]3+ (en = ethylenediamine), [Co(phen)3]3+ (phen = 1,10-phenanthroline), and [Co(CN)6]3−. It was revealed that appreciable amounts of multivalent ions are present as hidden ions on the lyomesophase, whose sign of charge is opposite to that of the ion in question. For such hydrophilic ions as [Co(NH3)6]3+, [Co(en)3]3+, [Co(CN)6]3−, and magnesium ions, the ions binding to the mesophases are classified into two states based on the NMR spectra: One is an outer-sphere complex (ion pair); the other is a hidden ion. In these systems the hidden ion/total ion population ratios depending on the composition of the surfactant are roughly proportional to the ion pair/total ion population ratios, which are monitored by the magnitude of the quadrupole splitting. For the phen complex, the presence of a hidden ion was observed in the range where the fraction of the anionic surfactant is high; the quadrupole splittings were also observed only in limited composition ranges.