15365-75-0Relevant academic research and scientific papers
Magnetic Separation of Metal Ions
Chie,Fujiwara,Fujiwara,Tanimoto
, p. 14374 - 14377 (2003)
The magnetic separation was investigated for Co2+ (9500 ?? 10-6 cm3 mol-1) and Fe3- (14600 ?? 10-6 cm3 mol-1) ions and for Cr 3+ (6200 ?? 10-6 cm3 mol-1) and Al3+ (-2 ?? 10-6 cm3 mol -1) ions. The metal ion solutions were spotted on a silica gel support, and exposed to a magnetic field of 410 kOe2 cm-1 intensity ?? gradient. The Co2+ ions move farther toward the maximum field than the Fe3+ ions. The result is explained by the fact that the Fe3+ ions are adsorbed more strongly on the silica gel surface than the Co2+ ions. The Cr3+ ions move farther toward the field center than the Al3+ ions. This occurs because the Cr3+ ions are attracted more strongly by the magnetic force than the Al3+ ions. It is demonstrated that the separation makes effective use of the adsorption activities as well as the magnetic susceptibilities.
Electromicrogravimetric study of underpotential deposition of Co on textured gold electrode in ammonia medium
Montes-Rojas, Antonio,Torres-Rodriguez, Luz Maria,Nieto-Delgado, Cesar
, p. 1769 - 1776 (2007)
Formation of a layer of a metal M on a foreign metal substrate, S, at potentials positive to its reversible potential, Er, (underpotential deposition, UPD) is a phenomenon that appears only in some systems. In the case of the UPD process of Co on a gold substrate, there is still a controversy about its existence, for which reason, in this study, voltammetry and chronoamperometry were coupled with a quartz microbalance in ammonium solution to better understand its formation mechanism. The results obtained show that the Co forms only one layer on the substrate before the bulk deposition of cobalt occurs. During the UPD process, the Co atom completely transfers its two electrons to the electrode and is adsorbed as a discharged species. The monolayer charge density, determined by electromicrogravimetry, is 448 μC cm-2 and probably corresponds to a commensurate overlayer on the gold substrate. In addition, the UPD process is controlled by adsorption as shown by voltammetric experiments. Finally, the analysis of the process of Co monolayer destruction (desorption) shows a mechanism different from that in the formation process, possibly due to H adsorption on the substrate produced during the process of adsorption of Co. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
Profiles of Co (NH3)62 + and Ni (NH3)62 + complexes in two-cation Liesegang systems
Badr, Layla,Sultan, Rabih
, p. 40 - 44 (2008)
Liesegang patterns of Co(OH)2 and Ni(OH)2 seemingly migrate in space as time advances because of redissolution of the bands in excess NH4OH. The formation of the complexes Co (NH3)62 + and
Reduction of Cobalt(III) Complexes by Intramolecular Electron Transfer from Bound Free Radicals. A Pulse Radiolytic Study
Cohen, Haim,Nutkovich, Mordchi,Meyerstein, Dan,Wieghardt, Karl
, p. 943 - 950 (1982)
The specific rates of reduction of 3+ by a series of nitrobenzoate and nitrogen heteroatomic anion radicals are reported.The rates of intramolecular electron transfer from the same anion radicals to a central cobalt(III) bound to them via a carboxylate group are reported, as well as for some pyrazine carboxylate anion radicals bound to the cobalt via the carboxylate and the N1 atom.The factors affecting the rate of intramolecular electron transfer processes are discussed in detail.
Magnetodynamic effects on outer-sphere electron-transfer reactions: A paramagnetic transition state
Ronco,Ferraudi
, p. 3961 - 3967 (2008/10/08)
The effect of the magnetic field on the rate of outer-sphere electron-transfer reactions has been investigated as a function of the field intensity, between 0 and 9 T, and at a given temperature. In complexes of d6 metal ions, i.e., Ru(II) and Co(III), the rate constant exhibits a complex dependence on the field: a complexity associated with field-induced changes of the electronic matrix element and the activation energy. Changes in the activation energy have been investigated as a function of the temperature at a given field intensity. These measurements have shown that the magnetic susceptibility of activation has the large positive values that are expected for a strongly paramagnetic transition state. The magnetic field effects are discussed in terms of symmetry-determined selection rules for the coupling of the initial and final electronic states of the reactions.
Effect of steric crowding on the rates of reactions of a nickel(I) tetraaza macrocycle with organic halides and hydroperoxides
Sadler, Novelette,Scott, Susannah L.,Bakac, Andreja,Espenson, James H.,Ram
, p. 3951 - 3954 (2008/10/08)
The reactions of the sterically crowded decamethylcyclam complex of nickel(I), Ni(dmc)+, with organic halides, hydrogen peroxide, and tert-butyl hydroperoxide occur some 104 times more slowly than the corresponding reactions of Ni(tmc)+, a tetramethylcyclam complex. This supports the assignment of an inner-sphere mechanism in both cases, because reactions that necessarily adopt an outer-sphere mechanism (e.g., those of cobalt(III) amine complexes) differ no more in their relative rates than can easily be explained by the small difference in driving force.
Spectroscopic Investigation of the Interaction of Co2(CO)8 with MgO and SiO2
Rao, Kanithi Mohana,Spoto, Giuseppe,Guglielminotti, Eugenio,Zecchina, Adriano
, p. 2195 - 2208 (2007/10/02)
Co2(CO)8, when absorbed in the gas phase, in vacuo, on fully dehydrated MgO, forms a variety of carbonyl clusters both neutral and ionic.These clusters disintegrate into monometallic species upon dosing with either CO or NH3, resulting in Co(CO)4- and Co2+(CO)n (n=2 or 3) with CO and Co(CO)4- and Co2+(NH3)6 with NH3, respectively.The negatively charged species are formed via several routes, including disproportionation and nucleophilic attack by O2- on the carbonyl groups of different cobalt carbonyl clusters.These effects are attributed to the strongly basic nature of the highly dehydroxylated magnesia used in the present investigation.Diffuse reflectance and e.s.r. spectral studies performed in similar conditions on magnesia confirm all these transformations.The results on a highly dehydrated SiO2 surface are quite different: Co2(CO)8 is mostly absorbed without appreciable chemical modification, giving two isomers containing linear and bridged CO.Only by removing CO by outgassing at the beam temperature, is the total transformation into Co4(CO)12 and possibly Co6(CO)12 observed.
Formation and Decomposition of Iron-Carbon ?-Bonds in the Reaction of Iron(II)-Poly(amino carboxylate) Complexes with CO2- Free Radicals. A Pulse Radiolysis Study
Goldstein, Sara,Czapski, Gidon,Cohen, Haim,Meyerstein, Dan
, p. 3903 - 3907 (2007/10/02)
The reactions of ferrous poly(amino carboxylate) complexes with CO2- were studied at neutral pH in aqueous solutions.The results indicate that complexes with metal-carbon ?-bonds are formed as unstable intermediates with maximum absorption bands at 405 nm (e = 620 +/- 50 M-1 cm-1) and at 420 nm (e = 950 +/- 100 M-1 cm-1) for the NTA and HEDTA complexes, respectively.The transient complexes are in equilibrium with the ferrous poly(amino carboxylate) complex and CO2- free radical.The stability constants for the complexes of CO2- with ferrous NTA and HEDTA complexes were determined to be larger than 1E5 M-1.The kinetics of formation and decomposition and possibile reaction mechanisms for these intermediates are discussed.We determined the specific rate constants for the formation of the iron-carbon ?-bonds (1.5 x 1E7 and 6.2 x 1E6 M-1 s-1 for NTA and HEDTA, respectively) as well as for the homolytic cleavage of the metal-carbon bond (140 and 25 s-1 for NTA and HEDTA, respectively).It is shown that the ferrous poly(amino carboxylate) complexes induce the disproportionation of the CO2-1 free radicals to form CO and CO2 via CO2- + L-FeIIICO22- with specific rate constants of 1.9 x 1E7 and 4.5 x 1E6 M-1 s-1 for L = NTA and HEDTA, respectively.
Charge-Transfer Perturbations of the Electronic Contributions to Electron-Transfer Reactions. Enhanced Donor-Acceptor Couplings Mediated by Coordinated Ligands
Endicott, John F.,Ramasami, T.
, p. 3740 - 3747 (2007/10/02)
The factors contributing to variations in the adiabaticity of a series of Co(III)-Co(sep)(2+) (sep= (S)-1,3,6,8,10,13,16,19-octaazabicycloeicosane) cross-reactions have been investigated.Coordinated ligands can be effective in making the electron-transfer rates more adiabatic by altering the electronic structure of the complex and/or by contributing to intermolecular charge-transfer interactions.Alterations of the coordinated ligands change both the ligand field and the charge-transfer excited states of the Co(III) acceptor, and the contributions of each kind of excited state perturbation must be considered in evaluating rate patterns.For Co(NH3)5X(2+) oxidants, the inferred values of the electronic transmission coefficient, κel, increase systematically through the series X=CN, Cl, Br, N3, and I with the smallest value of κel being ca. 10-3 and the largest approaching unity.Simple models are proposed which account for the variations in κel based on the perturbational effects of ligand to metal charge transfer and triplet ligand field excited states on the electron exchange integral coupling reactants and products.
Stabilization of the monovalent nickel complex with 1,4,8,11-tetraazacyclotetradecane in aqueous solutions by N- and C-methylation. An electrochemical and pulse radiolysis study
Jubran, Nusrallah,Ginzburg, Gregory,Cohen, Haim,Koresh, Yaacov,Meyerstein, Dan
, p. 251 - 258 (2008/10/08)
The divalent nickel complexes with 1,4,8,11-tetraazacyclotetradecane (L1), 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (L2), meso-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (L3), and 1,4,5,7,7,8,11,12,14,14-decamethyl-1,4,8,11-tetraazacyclotetradecane (L4) were reduced by reactions with eaq- and CO2-? and by electrochemical reactions in aqueous solutions. The redox potentials of the NiLi2+/NiLi+ couples are -1.58, -1.15, -1.42, and -0.98 V vs. SCE for i = 1, 2, 3, and 4, respectively. The UV absorption bands of NiLi+ are attributed to CTTS transitions. The kinetics of reduction of Co(NH3)63+, Ru(NH3)63+, O2, and N2O by NiLi+ are reported and discussed. The self-exchange rates of reaction between NiLi+ and NiLi2+ were calculated by using the Marcus cross relation. The EPR spectra of NiL2+ and NiL4+ are reported. The complexation of NiLi2+ by OH- was studied. The results are discussed in detail. NiL2+ and NiL4+ are suggested as new, powerful, easily attainable single-electron-reducing agents that can be used over a wide pH range in aqueous solutions.
