Rare cobalt compounds

Colour - A striking feature of transition-metal compounds is their colour. Whether it is the pale blue or pink hues of copper(ii) sulfate and cobalt(ii) chloride, or the intense purple of potassium permanganate, these colours tend to be associated most commonly with transition-metal compounds. It is rare for compounds of main group metals to be highly coloured. 

About structures of lithium compounds LisMeFs we have but rare knowledge. Klemm, Brandt and Hoppe (193) report in accordance with Meyers and Cotton (225) that the x-ray-diagrams of the cobalt compound LisCoFe were of a poor quality. The polymorphism that Carton and Wanklyn (108) report of the aluminium compound LisAlFe points to a more complicated situation in this ternary fluoride. The sizes given of the unit cells do not show any simple relation to the cryolite cell. The same may be true of compounds LisMeFa of the transition metals. 

C. The Rare Earth-Cobalt Compounds 1. TheRCo2 Series... 

Vitamin B,2 is a cobalt complex. It is essential for good health in man and without it pernicious anaemia will eventually result in death. The vitamin is not synthesised in the human body and has to be obtained from food, mostly meat and dairy products, or micro-organisms. It is the only vitamin which contains a metal ion and furthermore it is often found in vivo with a cobalt-carbon bond - one of Nature s rare organometallic compounds. It is usually used in the laboratory as the beautiful red crystalline solid, which is the cyano-complex. The structure of vitamin B12 was originally determined using this compound, cyanocobalamin, and this is shown in Figure 7.21. The cyano-species is only found in the bodies of people who smoke The cyanide is... 

In addition to the Kirchmayr-Poldy review, additional information concerning the magnetic behaviors of rare earth compounds are found in the reviews by Buschow (1977, 1979), Nesbitt and Wernick (1973), Taylor and Darby (1972) and Wallace (1973). The review by Nesbitt and Wernick is exclusively on rare-earth-cobalt permanent magnets, while the others generally cover a wide range of compounds. 

Interestingly, a case of allergic contact dermatitis due to cobalt-2-ethylhexoate in a Finnish offset printer has been reported (Kanerva et al. 1996). It is used as a paint and ink drier, whitener and catalyst. Although isolated cobalt allergy is rare, cobalt salts are well-known sensitisers, and this has long been recognised in painters. Dermatitis patients in contact with inks, paints or varnishes need to be patch tested with cobalt, which is routine, as cobalt chloride is a member of the standard series however its potential occupational relevance may well be overlooked. Ethoxylated phenol and its phosphate salt have been described as sensitisers (Ashworth 1991) these compounds are used as surfactants in plate developers. 

Magnetic properties of rare earth-cobalt compounds and their hydrides. 

R2M12P7. The unit-cell plot of R2M12P7 compounds (table 80 fig. 91) probably indicates a different valence state fi-om R " for cerium (in compounds with Fe, Co, Ni, Rh), europium (with Ni) and ytterbium (with Rh and Ni) atoms. The magnetic moment on the transition-metal atoms is observed only in cobalt compounds, magnetic properties of all other R2M12P7 compounds are caused by rare-earth atoms. 

Naturally occurring compounds with carbon-metal bonds are very rare The best example of such an organometallic compound is coenzyme Bi2 which has a carbon-cobalt ct bond (Figure 14 4) Pernicious anemia results from a coenzyme B12 deficiency and can be treated by adding sources of cobalt to the diet One source of cobalt IS vitamin B12 a compound structurally related to but not identical with coen zyme B12... 

Despite the above similarities, many differences between the members of this triad are also to be noted. Reduction of a trivalent compound, which yields a divalent compound in the case of cobalt, rarely does so for the heavier elements where the metal, univalent compounds, or hydrido complexes are the more usual products. Rhodium forms the quite stable, yellow [Rh(H20)6] " ion when hydrous Rh203 is dissolved in mineral acid, and it occurs in the solid state in salts such as the perchlorate, sulfate and alums. [Ir(H20)6] + is less readily obtained but has been shown to occur in solutions of in cone HCIO4. 

Cobalt(II) alkoxides are known and monomeric forms are part of a wider review.413 The interest in these compounds pertains to a potential role in catalysis. For example, a discrete cobalt(II) alkoxide is believed to form in situ from a chloro precursor during reaction and performs the catalytic role in the decomposition of dialkyl pyrocarbonates to dialkyl carbonates and carbon dioxide.414 A number of mononuclear alkoxide complexes of cobalt(II) have been characterized by crystal structures, as exemplified by [CoCl(OC(t-Bu)3)2 Li(THF)].415 The Co ion in this structure and close relatives has a rare distorted trigonal-planar coordination geometry due to the extreme steric crowding around the metal. 

Metal-Carbon Compounds. Clear examples of olefin insertions into transition metal-carbon groups are rare. The obvious reaction of olefins with alkyl- or acyl-cobalt tetracarbonyls are slow, complicated, and incomplete under the usual laboratory conditions. Under high pressure at elevated temperatures, in the... 

Compounds with Metal—Metal Bonds. Additions of compounds with metal-metal bonds to acetylenes are rare. Perhaps the addition of acetylenes to cobalt octacarbonyl (29) should be considered an insertion reaction even though the metal-metal bond is not broken since the acetylene finally is bonded to both metal atoms. 

Thermodynamics and Kinetics of Hydrogen Absorption in Rare Earth-Cobalt (R2C07 and RC03) and Rare Earth-Iron (RFes) Compounds... 

GOUDY ET al. Rare Earth-Cobalt and -Iron Compounds... 

The intermetallic compounds were prepared from the best grade of metals commercially obtainable. The rare earth metals, obtained from Research Chemicals, Inc., were 99.9% pure, and cobalt and nickel, obtained from the United Mineral Corp., were 99.999% pure. After each element was weighed to obtain the correct stoichiometric amounts, the compounds were formed by induction melting in a water-cooled copper boat under an argon atmosphere, purified by passage through a titanium-gettering furnace. 

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