Transition metal cobalt

The cobalamins (7) are the chemically most complex form of coenzyme. They also represent the only natural substances that contain the transition metal cobalt (Co) as an essential component. Higher organisms are unable to synthesize cobalamins themselves, and are therefore dependent on a supply of vitamin Bi2 synthesized by bacteria (see p. 368). 

The transition metal cobalt has its own artistic history it is used to give a deep blue or sometimes green color to pottery and glass. Anyone who has played with a toy chemistry set has probably made invisible ink, another unusual cobalt product. Invisible ink is made from a compound of cobalt and chlorine. Dissolved in a mixture of water and a common liquid called glycerine, the ink becomes colorless. When a message written in the ink is heated, the water and glycerine break away from the... 

The reactions are catalyzed by transition metals (cobalt, iron, and ruthenium) on high-surface-area silica, alumina, or zeolite supports. However, the exact chemical identity of the catalysts is unknown, and their characterization presents challenges as these transformations are carried out under very harsh reaction conditions. Typically, the Fischer-Tropsch process is operated in the temperature range of 150°C-300°C and in the pressure range of one to several tens of atmospheres [66], Thus, the entire process is costly and inefficient and even produces waste [67]. Hence, development of more economical and sustainable strategies for the gas-to-liquid conversion of methane is highly desirable. 

The unusual nature of the red cobalt complex (I) induced considerable activity in the field of coordination chemistry vitamin B12 derivatives were found to represent unique examples of kinetically labile Co complexes, the analysis of whose model type coordination chemistry itself proved to be of particular value.Interestingly, for the transition metal cobalt, no other cofactor function has been clearly established, except for that in the B -derivatives. ... 

A new type of octaazamacrobicyclic Schiff bases was synthesized in high yields via a template condensation on Group 2 metal ions in ethanol at 40-50°C (Scheme 92) [196], The resultant kinetically labile complexes readily transmetallize when reacted with transition metal (cobalt, nickel, iron, copper(II)) salts to form the corresponding mononuclear [M(imBT)]X2 complexes (where X is BF4 and C104 ). 

Many normal oxides are formed on burning the element in air or oxygen. This is true not only of the non-metals boron, carbon, sulphur and phosphorus, but also for the volatile zinc, cadmium, indium and thallium, the transition metals cobalt and iron, in finely divided condition, and the noble metals osmium, ruthenium and rhodium. With some elements, limiting the supply of oxygen produces the lower oxide (e,g, P40g in place of P4O40 (p. 332)). 

Modem hydroformylation research is almost exclusively focused on four transition metals cobalt, rhodium, platinum and to considerable extent mthenium [13], The generally accepted order of hydroformylation activity for unmodified monometallic catalysts clarifies this picture [14] ... 

With a single-line source, two photochemically active components can be separated in solution by irradiation and subsequent reaction of one of the components. This technique has been applied to the separation of the transition metals cobalt and iron (10) and of europium from the other lanthanides (H). Although no separation of this type has been reported for the actinides, there is nothing in principle that prevents it. This method could prove particularly useful in separating actinides from lanthanides, where thermal chemical methods are particularly difficult. 

A variety of catalysts can be used for the Fischer-Tropsch process, but the most common are the transition metals cobalt, iron, and ruthenium. Nickel can also be used but tends to favor methane formation (methanation). 

Trace elements or microelements Occurring in even lower concentrations (tens of mg/kg or less) important trace elements are transition metals cobalt (Co), chromium (Cr), copper (Cu), Fe (sometimes), manganese (Mn), molybdenum (Mo), nickel (Ni) and sometimes zinc (Zn), post-transition metal aluminium (Al), the halogen iodine (1) and non-metal selenium (Se). 

Adipose tissue has been found to suffer chronic hypoxia during the development of obesity (Brook et al., 1972 Helmlinger et al., 1997), and these conditions may lead to metabolic disorders. Hypoxic conditions can be induced by the addition of certain chemicals called hypoxia mimetics, such as the carcinogenic transition metal cobalt (Vincent et al., 1996). It... 

In addition to the two crystal structures obtained in this study, six other coordination compounds have been synthesized and characterized [73, 84]. A complete spectroscopic study was performed involving squaraines 1,3- and 1,2-disubstituted with dicyanomethylene groups and four different transition metals cobalt, manganese, zinc, and nickel. The Raman and infrared spectra of all these complexes with both ligands reveal that the ligands exhibit an inverted symmetry element, meaning that the bands which are seen with one technique are not seen with the other, and vice versa. The complexation did not affect the molecular symmetry (in the case of the trans dianion) or the solid-state structure (in the case of the cis dianion). 

For trivalent cobalt, data are only available for the formation of the first monomeric hydrolysis species. The formation reaction for this species is described by Eq. (2.5) (M = Co, p=l, q=l)- It is possible that, like other trivalent first series transition metals, cobalt(III) forms higher monomeric species as well as dimeric and trimeric polymer species. However, no data are available for these species. 

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