Bivalent cobalt

The effect is so pronounced that covalent compounds of bivalent cobalt are difficult to prepare, decomposing water with the liberation of hydro-11 R. G. Dickinson, This Journal, 44, 2404 (1922). 

Several complexes of bivalent cobalt and zinc with imidazoline-(l//,3i/)-2-thione (34 R = H) of the forms ML2X2 (X = halide ion) and ML4X2 (X = N03 or C104) have been isolated and characterized by physicochemical techniques.247 In contrast with the S monodentate behaviour concluded for the earlier-reported Ni11 complexes, the ligands are N—S bidentate in these metal salts to form four-membered chelate rings. Similar coordination behaviour has been observed for the... 

It is of interest that covalent compounds of bivalent cobalt can decompose H2O with liberation of H2, whereas the trivalent cobalt ion decomposes H2O, liberating O2, being one of the most powerful oxidizing agents known (5). These materials should have a use in modern aerospace problems. 

Five-coordinated high-spin complexes of bivalent cobalt, nickel and copper with tris(2-dimethylaminoethyl)amine, M. Ciampolini and N. Nardi, Inorg. Chem., 1966, 5, 41. 

JOB] Job, P., About the bivalent cobalt, copper and nickel salts in hydrochloric and hydrobromic acids, Ann. Chim. (Paris), 6, (1936), 97-144. Cited on pages 140,153, 156,265. 

In the previous section efficient catalysis of the Diels-Alder reaction by copper(II)nitrate was encountered. Likewise, other bivalent metal ions that share the same row in the periodic system show catalytic activity. The effects of cobalt(II)nitrate, nickel(II)nitrate, copper(II)nitrate and zinc(ll)nitrate... 

Most commercial sorbic acid is produced by a modification of this route. Catalysts composed of metals (2inc, cadmium, nickel, copper, manganese, and cobalt), metal oxides, or carboxylate salts of bivalent transition metals (2inc isovalerate) produce a condensation adduct with ketene and crotonaldehyde (22—24), which has been identified as (5). 

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. 

Nickel sulfate forms double salts with ammonium or alkali metal sulfates. For example, blue-green hydrated ammonium nickel sulfate, (NH4)2S04 NiS04 6H20, crystallizes from a mixed solution of nickel sulfate and ammonium sulfate. Such double sulfates are isomorphous to corresponding alkali metal or ammonium double sulfates of iron, cobalt, magnesium, zinc, and other bivalent metals. 

The oxidation of propene to acrolein has been one of the most studied selective oxidation reaction. The catalysts used are usually pure bismuth molybdates owing to the fact that these phases are present in industrial catalysts and that they exhibit rather good catalytic properties (1). However the industrial catalysts also contain bivalent cation molybdates like cobalt, iron and nickel molybdates, the presence of which improves both the activity and the selectivity of the catdysts (2,3). This improvement of performances for a mixture of phases with respect to each phase component, designated synergy effect, has recently been attributed to a support effect of the bivalent cation molybdate on the bismuth molybdate (4) or to a synergy effect due to remote control (5) or to more or less strong interaction between phases (6). However, this was proposed only in view of kinetic data obtained on a prepared supported catalyst. 

The bivalent ions of cadmium, cobalt, and copper, in concentrations of the order of 10-100 fiM, accelerate inactivation in experiments of the type shown in Figs. 4 and 5. An excess of Zn2+ prevents, or reverses, inactivation by these ions. 

The ion-exchange reaction of the synthetic zeolites NaX and NaY with cobalt, zinc and nickel ions is shown to be non-stoichiometric at low bivalent-ion occupancy, the hydrolytic sodium loss being about twice as large for NaX ( 5 ions/unit cell) as for NaY. The effect is more pronounced at high temperatures and disappears at high occupancies. Reversibility tests in NaX toward zinc and cobalt ions, as studied by a temperature-variation method, show the temperature history to be an important factor in the irreversibility characteristics. The low-temperature partial irreversibility, induced by a high-temperature treatment (45°C) is interpreted in terms of a temperature-dependent occupancy of the small-cage sites by divalent cations, which become irreversibly blocked at low temperature (5°C). 

Figure 1. Stoichiometry factor vs. bivalent ion occupancy in NaX (upper curve) and NaY (lower curve) at 25°C for cobalt (squares), nickel (circles), and zinc (triangles) (---------------) confidence interval at 95% level...

Reversibility. Apparent irreversibility phenomena of ion exchange in NaX were studied with zinc and cobalt ions using a temperature-variation method described in the experimental section. In view of the high selectivity of NaX for bivalent cations at low zeolite loading, the concentration of bivalent ions in the equilibrium solution is quite sensitive to small changes in the surface composition. In fact, the adsorption removal of bivalent cations at low loading, below 0.2, is quantitative or nearly so (99.5% or better). Consequently the value of the equilibrium concentration is an ideal criterion for assessing either reversibility or equilibrium conditions. 

The most important point is the effect of thermal history upon the equilibrium level of cobalt and zinc ions in solution. Within experimental error, the results obtained with the 45 °C—two day systems are identical to the 45°C systems which had received a prior one-day treatment at 5°C. The duration of the experiments has very little effect upon the equilibrium distribution, as evidenced by the fact that the results obtained by longterm equilibrations at both temperatures and for both ions were nearly identical to those shown in Table III. Most important however is the finding that the equilibrium levels of cobalt and zinc at 5°C are significantly higher than these which are obtained after a 45°C treatment. This indicates that the 5°C distribution over the various possible sites, as induced by a 45°C pretreatment, differs from the normal low-temperature distribution in that a significant portion of the adsorbed bivalent ions which participate in the 45°C equilibrium no longer do so at 5°C. In other words, when returned to 5°C, part of the solid-phase metal ions appear irreversibly sequestered in sites where they are out of reach at low temperature. 

Although square-planar configuration is customarily considered classical for v/c-dioximate of nickel(II), attempts have been made repeatedly over the years for preparing the above complexes in other configurations also. By employing weakly polar solvents and some other variations, success has been claimed in the preparation of mono(dioxime) complexes of nickel(II).42,43 The dichloro-bis(l,2-cyclohexanedione dioximato)nickel(II) has been shown to have an octahedral vie structure.44 Examples of tris(dioxime) complexes of transition metals in general45"18 and of bivalent atoms40,47 in particular are rare and structural details of only a tris(dioxime) complex of cobalt(III) are known.48 In a more recent publication,49 the crystal structure of tris(l,2-cyclohexanedione dioximo)nickel(II) sulfate dihydrate has been elucidated. 

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