Cobalt equilibrium

There is another possibility which was applied for interpretation of adsorption of organic ions [34,74]. One measures the effect of pH on the adsorption of cobalt ions at their different total concentrations. Simultaneous electrokinetic measurements provide the concentrations at isoelectric point so that each experimental run would yield the adsorption amounts and cobalt equilibrium concentration at zero electric potential. Regardless to different... 

Although this experiment is written as a dry-lab, it can be adapted to the laboratory. Details are given for the determination of the equilibrium constant for the binding of the Lewis base 1-methylimidazole to the Lewis acid cobalt(II)4-trifluoromethyl-o-phenylene-4,6-methoxysalicylideniminate in toluene. The equilibrium constant is found by a linear regression analysis of the absorbance data to a theoretical equilibrium model. 

Analogously, pyrazolyl-aluminate and -indate ligands have been prepared <75JCS(D)749) and their chelating properties evaluated with cobalt, nickel, copper and zinc. Gallyl derivatives of pyrazoles and indazoles have been extensively studied by Storr and Trotter e.g. 75CJC2944) who determined several X-ray structures of these compounds. These derivatives exist in the solid state as dimers, such as (212) and (288). A NMR study in acetone solution showed the existence of a slow equilibrium between the dimer (212) and two identical tautomers (289) and (290) (Section 4.04.1.5.1) (81JOM(215)157). 

A number of metals, such as copper, cobalt and h on, form a number of oxide layers during oxidation in air. Providing that interfacial thermodynamic equilibrium exists at the boundaries between the various oxide layers, the relative thicknesses of the oxides will depend on die relative diffusion coefficients of the mobile species as well as the oxygen potential gradients across each oxide layer. The flux of ions and electrons is given by Einstein s mobility equation for each diffusing species in each layer... 

Clausius-Clapeyron equation An equation expressing the temperature dependence of vapor pressure ln(P2/Pi) = AHvapCl/Tj - 1/T2)/R, 230,303-305 Claussen, Walter, 66 Cobalt, 410-411 Cobalt (II) chloride, 66 Coefficient A number preceding a formula in a chemical equation, 61 Coefficient rule Rule which states that when the coefficients of a chemical equation are multiplied by a number n, the equilibrium constant is raised to the nth power, 327... 

The same sort of competition for electrons is involved in reaction (11), in which Zn(s) releases electrons and Cu+2 accepts them. This time the competition for electrons is such that equilibrium favors Zn+2 and Cu(s). By way of contrast, compare the reaction of metallic cobalt placed in a nickel sulfate solution. A reaction occurs,... 

The tautomerization is induced by cobalt(II) which forms the thermodynamically more stable metalatcd hydroporphyrins from which the cobalt can be removed using trifluoroacctic acid under kinetic control. Experiments with porphyrinogen and hexahydroporphyrin show that the porphyrinogen-hexahydroporphyrin equilibrium can be shifted by complexation of porphyrinogen with metal ions to the more stable metal hexahydroporphyrins and that metal-free hexahydroporphyrins tautomerize back to the more stable metal-free porphyrinogens.29... 

Cobalt, tetraamminepyrophosphato-structures, 1, 202, 203 Cobalt, tetraammine(sarcosine)-chirality, 1,198 Cobalt, triammine-structure, 1, 8—10 Cobalt, tricarbonato-reactions, 1,22 Cobalt, tricarbonylnitroso-exchange reactions, 1, 290 Cobalt, trichloro-equilibrium constant, 1, 517 Cobalt, trichlorobis(triethylphosphine)-structure, 1, 45... 

The reaction does not feature a bimolecular step, such as direct Sn2 attack of the hydroxide nucleophile on the cobalt center. Rather, hydroxide ion participates in a prior-equilibrium reaction, and the actual rate-controlling reaction is believed to be the uni-molecular expulsion of the leaving group from a species that contains a coordinated... 

Prior equilibrium. Consider the net reaction between certain metal halide and alkyl cobalt complexes, RCo + MX = Co+ + RM + X". There is a rapid equilibrium ... 

It is interesting to note, as pointed out to me by Mr. J. L. Hoard, that these considerations lead to an explanation of the stability of trivalent cobalt in electron-pair bond complexes as compared to ionic compounds. The formation of complexes does not change the equilibrium between bivalent and trivalent iron very much, as is seen from the electrode potentials, while a great change is produced in the equilibrium between bivalent and trivalent cobalt. 

With a view to determining the equilibrium constant for the isomerisation, the rates of reduction of an equilibrium mixture of cis- and rra/i5-Co(NH3)4(OH2)N3 with Fe have been measured by Haim S . At Fe concentrations above 1.5 X 10 M the reaction with Fe is too rapid for equilibrium to be established between cis and trans isomers, and two rates are observed. For Fe concentrations below 1 X lO M, however, equilibrium between cis and trans forms is maintained and only one rate is observed. Detailed analysis of the rate data yields the individual rate coefficients for the reduction of the trans and cis isomers by Fe (24 l.mole sec and 0.355 l.mole .sec ) as well as the rate coefficient and equilibrium constant for the cw to trans isomerisation (1.42 x 10 sec and 0.22, respectively). All these results apply at perchlorate concentrations of 0.50 M and at 25 °C. Rate coefficients for the reduction of various azidoammine-cobalt(lll) complexes are collected in Table 12. Haim discusses the implications of these results on the basis that all these systems make use of azide bridges. The effect of substitution in Co(III) by a non-bridging ligand is remarkable in terms of reactivity towards Fe . The order of reactivity, trans-Co(NH3)4(OH2)N3 + > rra/is-Co(NH3)4(N3)2" > Co(NH3)sN3 +, is at va-... 

An example for a compound of the perovskite type is LaNiOj. In other com-ponnds of the perovskite type, nickel may be replaced by cobalt or iron, and lan-thannm in part by alkaline-earth metals, an example being Lag 8Sro2Co03. The activity of perovskites toward cathodic oxygen reduction is low at room temperature but rises drastically with increasing temperature (particularly so above 150°C). In certain cases the activity rises so much that the equilibrium potential of the oxygen electrode is established. 

An unusually slow relaxation has been observed for the 2,6-pyridine-dicarboxaldimine cobalt(II) complex [Co(2,6-(CH3NH=CH)2py)2](PFg)2 in solution. Thus a relaxation time -c = 83 ns has been reported [99], the rate constants being among the lowest found. It has been suggested that nonelectronic factors such as partial ligand dissociation, steric effects or solvent interaction may be rate determining in this equilibrium. 

Drawing a Conclusion The equilibrium system for the cobalt chloride solution may be expressed as follows ... 

Bied-Charreton (63) showed by XH NMR spectroscopy that a zinc porphyrin bearing a primary amino group attached via a flexible spacer to the meta position of a /neso-phenyl ring spontaneously dimerizes in solution via NH Zn coordination. The corresponding ortho derivative shows an equilibrium between the dimeric form and the intramolecu-larly coordinated monomer. ESR spectroscopy was used to demonstrate the same behavior in the corresponding cobalt porphyrin (64). 

Coprecipitation is a partitioning process whereby toxic heavy metals precipitate from the aqueous phase even if the equilibrium solubility has not been exceeded. This process occurs when heavy metals are incorporated into the structure of silicon, aluminum, and iron oxides when these latter compounds precipitate out of solution. Iron hydroxide collects more toxic heavy metals (chromium, nickel, arsenic, selenium, cadmium, and thorium) during precipitation than aluminum hydroxide.38 Coprecipitation is considered to effectively remove trace amounts of lead and chromium from solution in injected wastes at New Johnsonville, Tennessee.39 Coprecipitation with carbonate minerals may be an important mechanism for dealing with cobalt, lead, zinc, and cadmium. 

It is quite certain that the two cobalamin species with coordinated and free benzimidazole are in rapid equilibrium. However, the ligands bound to the lower coordination site are apparently not always easily displaced. As mentioned above, Brodie and Poe (130) have found that in DMSO, a water molecule is firmly bound to the sixth coordination position of alkyl cobinamides. Thus, even though DMSO is a good Lewis base, it will not easily displace water from the primary coordination sphere of the cobalt. 

A typical example of this is the dicobalt octacarbonyl catalyzed hydroformylation of olefins to yield aldehydes. According to the classical mechanism proposed by Heck and Breslow /29/ (Equations 28-31), the cobalt carbonyl reacts with hydrogen to form hydrido cobalt tetracarbonyl, which is in equilibrium with the coordinatively unsaturated HCo(C0)2. The tricarbonyl coordinates the olefin, and rearranges to form the alkyl cobalt carbonyl. 

Using the tri-iodide/iodide redox couple and the sensitizers (22) and (56), several groups have reported up to 8-10% solar cell efficiency where the potential mismatch between the sensitizer and the redox couple is around 0.5 V vs. SCE. If one develops a suitable redox couple that decreases the potential difference between the sensitizer and the redox couple, then the cell efficiency could increase by 30%, i.e., from the present value of 10% up to 13%. Towards this goal, Oskam et al. have employed pseudohalogens in place of the triiodide/iodide redox couples, where the equilibrium potential is 0.43 V more positive than that of the iodide/iodide redox couple.17 Yamada and co-workers have used cobalt tris-phenanthroline complexes as electron relays (based on the CoII/m couple) in dye-sensitized solar cells.95... 

Cfs-butene should lead initially to the anti form trrms-butene should lead initially to the syn form and 1-butene should give rise initially to both. The equilibrium distribution of syn and anti forms usually differs greatly from the equilibrium distribution of cis- and frans-butene for cobalt complexes 59, 60) the syn form, precursor of irans-butene, is by far the most stable. By way of contrast for the corresponding carbanion, the cis anion seems by far the more stable. This preference for the cis carbanion is presumed to be the source of the high initial cis-to-trans ratio in the initial products of base catalyzed isomerization. In the base catalyzed isomerization of more complex cf-s-olefins (cfs-S-methyl-stilbene), the ions corresponding to syn and anti are not interconvertible and cis-trans isomeriza-... 

The equilibrium, room temperature structure of pure cobalt is hep. The fee structure is stable at high temperatures (422 °C to 1495 °C) and has been retained at room temperature by rapid solidification techniques [101], X-ray diffraction analysis was used to probe the microstructure of bulk Co-Al alloy deposits containing up to 25 a/o Al and prepared from solutions of Co(II) in the 60.0 m/o AlCfi-EtMelmCl melt. Pure Co deposits had the hep structure no fee Co was observed in any of the deposits. The addition of aluminum to the deposit caused a decrease in the deposit grain size and an increase in the hep lattice volume. A further increase in the aluminum content resulted in amorphization of the deposit [44], Because the equilibrium... 

It was concluded that in this case an equilibrium existed which gave 100 ppm of soluble cobalt at reaction temperature. The polymer support acted as a reservoir for furnishing soluble metal at reaction temperature and reabsorbing it after completion (about 10 ppm in the product after cooling to ambient temperature). The rate approximated that obtained in a standard cobalt reaction with 100 ppm of cobalt catalyst. 

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