Cobalt equilibrium constants

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. 

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... 

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... 

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-... 

The kinetic effects of C02 in the base catalyzed hydrolysis of some carboxylato amine cobalt(III) complexes have been reported (80-82). In the base catalyzed hydrolysis of oxalatopentaammine-cobalt(III) (80), C02 retarded the reaction due to the formation of a virtually unreactive ion-pair, f (N H .) r, 2 2 COi ]. The equilibrium constant for formation of carbonate ion-pairs with (glycinato-O) (tetraethylene-pentamine)cobalt(III), (81) and (o-methoxybenzoato) (tetraethylenepentamine)cobalt(III) (82) were, however, much smaller than for the oxalatopentamminecobat(III) and a very weak rate retardation and virtually no effect was observed in the base catalyzed hydrolysis of the latter two complexes. 

Measurements of the equilibrium constants of the reactions imply that the stabilities of the monosubstituted complexes are predominantly determined by steric effects of the ligand, reflecting a very crowded space around the metal in this system. The large ligands PPh3 or P(c-C6H,) do not react with the cobalt complex. 

Reaction of Cytochrome cimu with Tris(oxalato)cobalt(III) The cytochrome c protein was also used as reductant in a study of the redox reaction with tris (oxalato)cobalt(III).284 Selection of the anionic cobalt(III) species, [Conl(ox)3]3 was prompted, in part, because it was surmised that it would form a sufficiently stable precursor complex with the positively charged cyt c so that the equilibrium constant for precursor complex formation (K) would be of a magnitude that would permit it to be separated in the kinetic analysis of an intermolecular electron transfer process from the actual electron transfer kinetic step (kET).2S5 The reaction scheme for oxidation of cyt c11 may be outlined ... 

Nickel and cobalt often occur with copper, and must be separated in pure form from hydrometallurgical leach liquors. Organic acid extractants can quite readily separate copper from cobalt and nickel, but the separation of cobalt from nickel is rather difficult. In one Ni/Co separation process, di-2-ethyl hexyl phosphoric acid (D2EHPA) is used as extractant, with strict control of the pH of the aqueous phase to take full advantage of the slightly different equilibrium constants for the Co and Ni reactions. Pulsed column contactors are used rather than mixer-settlers, and nickel impurity is removed from the loaded organic phase by scrubbing it with a cobalt-rich phase. 

Complexes of cobalt (III) containing coordinated perrhenate ion have not previously been reported. % They are of special interest because of their close relationship to the unstable perchlorate complexes and are of use in studies on the mechanism of hydrolysis. Since the equilibrium constant of formation is small and [Co(NH )5(HjO)](Re04) -2H20 is relatively insoluble, the present procedure is similar to that used previously for mom common complex ions. 

Equilibrium. Reactions of the type depicted by Equation 16 have been identified as synthetic routes to or-ganocobalt compounds (17, 18). Cobalt-alkyl bond-dissociation energies could be deduced from the enthalpies of such reactions if the latter could be determined, for example from the temperature dependence of the corresponding equilibrium constants. 

The degree to which the reaction can proceed is the greater the further apart both substances are in the standard potential series. Thus e. g. from the potential values of the elements Zn Zn++ and Pt I Co++, Co+++ it follows that the equilibrium constant of the reaction % Zn -f- Co+++ = Co++ -f- % Zn++ at 25 °C is approximately K = 1044, which means that the salt of the trivalent cobalt is reduced by zinc almost completely. The equilibrium constant K — 6.4 will belong on the other hand to the reaction Fe + Cd++ = Cd + Fe++ this comparatively small value shows a considerable amount of cadmium ions remaining in a state of equilibrium and not reduced. 

Under these experimental conditions, the equilibrium constant of cobalt-calcium ion exchange in montmorillonite cannot precisely be determined for two reasons. First, for the determination of the equilibrium constant, the integration has to be in the whole range of X. It is seen in Figure 2.8 (and it is in good agreement with the data in Table 2.7) that there is a surface concentration range (XCa = 0.8-1... 

Although a statistical factor contributes to the equilibrium constants for many types of reactions, it is in reactions of the type being considered here—the replacement of one neutral ligand by another neutral ligand— that this factor may be the principal factor in causing variation of Kn with n. Other series of reactions of this type are the formation of ammonia complexes in aqueous solution. The variation of Kn with n observed for the chromium (III)/water-methyl alcohol system is slightly smaller than observed for ammonia complexes of cobalt(II) (18) and nickel(II) (19) ... 

Granted quasi-equilibrium of ligand exchanges and neutralizations and the fact that Co(CO)3Ph is catalytically inactive and accounts for only an insignificant fraction of total cobalt, the system 8.13 can be modeled with two of the three equilibrium constants linking the concentrations of HCo(CO)3Ph, HCo(CO)4, and Co(CO)4 . This will be shown in more detail in Example 8.11 in Section 8.8.2. 

When Y is HgO the concentration of free H2O is ignored and the constants are expressed in units of liters per mole. In the cobalamins the base (Bz) which is normally coordinated to the cobalt is also attached to a side chain of the corrin. The equilibrium constant for the displacement of Bz by H2O can therefore be written... 

The polarographic determination of manganese, iron, cobalt and nickel is not so often used as that of the above mentioned elements. Probably, competition with other analytical methods is the main reason. However, the polarography of these metals has been thoroughly investigated and it is frequently used for studies of equilibrium constants of their complexes. 

The inertness of the dinuclear complexes is greatest in slightly acidic solutions, which therefore have been employed for the reprecipitation reactions. Apparently the chromium systems are much more labile toward bridge breaking than are the cobalt systems. In aqueous solution the meso-[(en)2Cr(OH)2Ci(en)2] cation (I) enters into a rapidly established (t 1 min. at room temperature) equilibrium with the mono-ju-hydroxo complex [(OHXen)2Cr(OH)Cr(en)2-(HaO)] (n) The equilibrium constant K = [II]/[I] is 0.83 in 1 Af NaC104 at 0°. The salts (dithionate, bromide, chloride, and perchlorate) of the di-p-hydroxo cation are less soluble than the respective salts of the mono-/i-hydroxo cation. It is therefore possible to precipitate the pure salts of the di-/i-hydroxo cation from the equilibrium mixture following the procedure given above. 

The cobalt(II) cyclidene product VI is reasonably stable toward autoxidation in the solid state, and a solid state IR spectrum can be obtained under aerobic conditions. The cobalt(II) complex is best identified by its ESR spectrum in an acetonitrile-1.5M M-methylimidazoIe solution, frozen to a glass at — 196 C a 2.3 and 2.00. Exposure of the thawed solution to O2 then causes replacement of this spectrum with that of the 1 1 Oj adduct % 2% 2.01 and 3% 2.08. At 20 °C in 2.5 M aqueous N-methylimidazole the complex binds dioxygen reversibly with an equilibrium constant Kq = 1.6 torr. An X-ray structure of the cobalt(II) complex confirms the presence of the commodious lacuna, which protects the coordinated dioxygen from autoxidation in polar sol vents.An X-ray structure determination of the dioxygen adduct, prepared by recrystallization of the complex from aqueous V-methylimidazole exposed to the atmosphere, confirms the existence and nature of the O, adduct. ... 

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