Cobalt, Co Ar

26 COBALT, Co (Ar 58-93) Cobalt is a steel-grey, slightly magnetic metal. It melts at 1490°C. The metal dissolves readily in dilute mineral acids  

The dissolution in nitric acid is accompanied with the formation of nitrogen oxide  

In aqueous solutions cobalt is normally present as the cobalt(II) ion Co2+ sometimes, especially in complexes, the cobalt(III) ion Co3+ is encountered. These two ions are derived from the oxides CoO and Co203 respectively. The cobalt(II)-cobalt(III) oxide Co304 is also known. 

In the aqueous solutions of cobalt(II) compounds the red Co2+ ions are present. Anhydrous or undissociated cobalt(II) compounds are blue. If the 

Cobalt(III) ions Co3+ are unstable, but their complexes are stable both in solution and in dry form. Cobalt(II) complexes can easily be oxidized to cobalt(III) complexes. 

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Cobalt (Co, [Ar]3 J74s2), name from the German word kobold (evil spirit). Isolated (1735) by the Swedish chemist Georg Brandt. 

Ozin, Hanlan, and Power, using optical spectroscopy (49,121). In view of the marked temperature-effect observed for the cobalt system, we shall focus on this cluster system here. Evidence for cobalt-atom aggregation at the few-atom extreme first came from a comparison of the optical data for Co Ar — 1 10 mixtures recorded at 4.2 and 12 K (see Fig. 4). A differential of roughly 8 K in this cryogenic-temperature regime was sufficient to cause the dramatic appearance of an entirely new set of optical absorptions in the regions 320-340 and 270-280 nm (see Fig. 4). Matrix variation, from Ar, to Kr, to Xe, helped clarify atom-cluster, band-overlap problems (see Fig. 5). 

The effect of deposition temperature on the clustering ability of Co atoms to form small, cobalt clusters was most revealing in terms of optical assignments, as well as activation-energy considerations. A series of runs with Co Ar — 1 10 deposited at 4.2, 12, 20, 25, 30, and 35 K (see Fig. 4) nicely demonstrated the gradual progression from isolated Co atoms to mixtures of Co/Coj to mixtures of C0/C02/C03. The most... 

The rhodium-catalyzed PK reaction has many unique features as compared to the original cobalt-mediated version. For example, most of the rhodium-catalyzed reactions could be carried out under only 1 atm CO. Initially, these reactions were expected to proceed more effectively under higher CO pressures. However, experimental results demonstrated that the reaction was retarded by elevated CO pressure (>1 atm.), while the reaction at a lower CO pressure (0.1 atm.) proved to be superior [13b]. For example, the reaction of la with [RhCl(CO)2]2 under a high pressure of CO (3 atm.) afforded 2a in 70% yield, but was not complete after 36 h. The analogous reaction under a mixed CO/Ar atmosphere (1 atm. CO/Ar=l 9) was complete within an hour to afford 2a in 90% yield. 

Low-valent cobalt [Co, Co° and Co" ] are known to complex with unconjugated dienes (e.g., 1,5-COD, NBD, etc.) and acetylenes. The Co or Co " precatalyst is presumably reduced by EtjAlCl to either Co° or Co. Co, which has the electronic configuration [Ar]3d and commonly forms five-coordinate complexes in a trigonal bipyramidal form. Thus, although very little is known about the structure of the catalytic intermediates, an intermediate with structures Ij and/or seems reasonable (Fig. 2). 

Similarly, reduction of the less crowded cobalt species Ar CoCl 2 with KCg in the presence of excess PMes afforded the related compound Co(ti 1 -(HaOaC-Ce... 

Cobalt monoboride crystals are deposited on a graphite substrate by simultaneous reduction with hydrogen of a mixture of CoClj (prepared in situ by chlorination of Co powder at 800°C) and BClj in an Ar flow ... 

Cobalt-supported-on-MgO catalysts were prepared by impregnating MgO (JRC-MGO-4 lOOOA, 14-16 m g ) with aqueous solutions of Co(N03)2-6H20 (Kanto Co.), followed by drying. The material was then calcined in air for 8 h at 873 K or 1173 K. Before catalytic tests, catalysts were reduced at 1173 K in H2/Ar (50/50 vol.%). 

Cobalt(II) Complexes. Spin conversion rates greater than 10 s have been estimated for [Co(terpy)2](PFg)2 [29]. Although Ar 0.04 A is available for the [Co(terpy)2] complex [132] there is a large uncertainty concerning the magnitude of electronic coupling. Therefore, no attempt has been made to calculate the rate constant. 

Studies of nitrosopentamminecobaitic saits such as red complex [Co(NH3)s (NO)] (N03)ar 0.5HjO. They are not listed in our tables 20a)J.L.Mil ward et al, JCS 1938, 233-6 CA 32, 8296(1938) (Constitution of nitrosopent-ammine cobalt salts, among them the compd listed in the previous reference) 2l)R. Duvai, CR 206, 1652-4(1938) CA 32, 5720 (1938) [Studies of trinitrotriamminocobalt (III) [Co(NHs)3 (NOj)s] (See item Co2 in table B) 22)W.Strecker E.Schwinn,JPraktChem 152, 205-18(1939) CA 33, 5314(1939)1 Introduction of the azide group into complex compds to replace Cl was studied. Among the compds prepd were several ammines such as diamminecadmium(II)azide, diam-minecopper(II) azide, tetramminecopper(II) azide, chloropentamminechrome(lll) azide, hexamminechrome(Ul) azide and hexam-minenickel(II) azide (See items Cdl, Cr5,... 

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