Structures cobalt

In contrast with the role of cofactor B12 in methionine synthase (methyl group transfer to a thiol), functional Bi2 model complexes have provided a formidable challenge. Several oxime alkyl-cobalt (structural) B12 models when reacted with arene- and alkanethiolates lead only to... 

The molecular structure of the manganese dimer clearly reveals that there is an Mn—Mn bond (Fig. I5.la. b). In the cobalt structure, two of the CO ligands are bridging, i.e.. they are simultaneously bound to both Co atoms (Fig. IS.Ic, d). This does not affect the electron count, however, because CO and other neutral ligands donate two electrons to a complex whether they are terminal or bridging (Table IS. I) ... 

Cobali [[) oxide, CoO. Olive green solid (heat on Co(OH)2 or cobalt(Il) oxyacid salt in absence of air) with NaCl structure. 

Parks E K, Winter B J, Klots T D and Riley S J 1992 Evidence for polyicosahedral structure in ammoniated iron, cobalt and nickel clusters J. Chem. Rhys. 96 8267... 

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... 

Analogously, pyrazolyl-aluminate and -indate ligands have been prepared <75JCS(D)749) and their chelating properties evaluated with cobalt, nickel, copper and zinc. Gallyl derivatives of pyrazoles and indazoles have been extensively studied by Storr and Trotter e.g. 75CJC2944) who determined several X-ray structures of these compounds. These derivatives exist in the solid state as dimers, such as (212) and (288). A NMR study in acetone solution showed the existence of a slow equilibrium between the dimer (212) and two identical tautomers (289) and (290) (Section 4.04.1.5.1) (81JOM(215)157). 

Good results are obtained with oxide-coated valve metals as anode materials. These electrically conducting ceramic coatings of p-conducting spinel-ferrite (e.g., cobalt, nickel and lithium ferrites) have very low consumption rates. Lithium ferrite has proved particularly effective because it possesses excellent adhesion on titanium and niobium [26]. In addition, doping the perovskite structure with monovalent lithium ions provides good electrical conductivity for anodic reactions. Anodes produced in this way are distributed under the trade name Lida [27]. The consumption rate in seawater is given as 10 g A ar and in fresh water is... 

Polymers containing 90-98% of a c 5-1,4-structure can be produced using Ziegler-Natta catalyst systems based on titanium, cobalt or nickel compounds in conjuction with reducing agents such as aluminium alkyls or alkyl halides. Useful rubbers may also be obtained by using lithium alkyl catalysts but in which the cis content is as low as 44%. 

Carbon monoxide has been found to poison cobalt molybdate catalysts. It causes not only instantaneous deactivation but a cumulative deactivation as well. It should be removed from treat gas entirely or at least reduced to a very low value. Carbon dioxide also must be removed since it is converted to CO in the reducing atmosphere employed in Hydrofining. Liquid water can damage the structural integrity of the catalyst. Water, in the form of steam does not necessarily hurt the catalyst. In fact 30 psig steam/air mixtures are used to regenerate the catalyst. Also, steam appears to enhance the catalyst activity in... 

C.-H. Kiang e o/.[33] reported that the singlelayered coiled lubes were obtained by co-vaporizing cobalt with carbon in an arc fullerene generator. A single-layered helical structure with radii of curvature as small as 20 nm was seen. These helically coiled forms lend to bundle together. In the soot obtained with sulfur-containing anodes, they also found the 1.3-nm diameter lube coil around the 3.6 nm tube (see Fig. 14). This kind of structure was theoretically proposed in ref. [14]. 

Quite recently, Ciampolini and coworkers have reported the synthesis of two isomeric mked oxygen-phosphorus macrocycles and the crystal structures of their cobalt complexes. Synthesis of macrocycle 27 was accomplished by condensation of 1,2-bis-(phenylphosphino)ethane dianion with 2,2 -dichlorodiethyl ether in THE. The two isomers of 27 were isolated in 1.5% and 2% yield. The synthesis is formulated in Eq. (6.17), below. 

FIGURE 18.28 The structure of cyanocobalamin (top) and simplified structures showing several coenzyme forms of vitamin Bi2- The Co—C bond of 5 -deoxyadenosylcobalamin is predominantly covalent (note the short bond length of 0.205 nm) but with some ionic character. Note that the convention of writing the cobalt atom as Co" " attributes the electrons of the Co—C and Co—N bonds to carbon and nitrogen, respectively. 

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