Co compounds

Other 5-coordinate Co compounds which have been characterized include [CoBr- N(C2H4NMe2)3 ]+, which is high-spin with 3 unpaired electrons and is trigonal bipyra-midal (imposed by the tripod ligand), and... 

The structures are shown in Fig. 26.8c and d and differ in that, whereas the Ir compound consists of a tetrahedron of metal atoms held together solely by M-M bonds, the Rh and Co compounds each incorporate 3 bridging carbonyls. A similar difference was noted in the case of the trinuclear carbonyls of Fe, Ru and Os (p. 1104) and can be explained in a similar way. The M4 tetrahedra of Co and Rh are small enough to be accommodated in an icosahedral array of CO ligands whereas the larger Ir4 tetrahedron forces the adoption of the less dense cube octahedral array of ligands. 

A range of bis-quaternary salts from various bases and a-co compounds is described by Libman et while the reactions of 4-amino-... 

Co 2p3/2 binding energies for CoOx/Ti02 catalysts and reference Co compounds... 

It is appropriate to identify our approach to developing the present review in the context of the Co chapter in CCC(1987). The first-edition chapter on Co featured a focused discussion and tabulation of synthetic methods, and many of these basic methods are still employed in synthesis today. Consequently, to avoid repetition, there will be diminished description here where prior appropriate methods have been provided, and only newer developments featured. The last two decades feature the development of many mixed-donor and sophisticated multidentate and macrocyclic ligands, which found limited coverage in the previous edition, and these will be discussed in more detail herein. Reaction kinetics and mechanism were also described thoroughly in the previous edition. We shall not reiterate this material, since the core mechanisms of many reactions involving Co compounds are now adequately defined. 

Dioxygen and its ions can bind in mononuclear and dinuclear structures in a number of ways,962 as illustrated in Scheme 1. The typical reaction of dioxygen with Co compounds involves a number of these binding forms, outlined in Scheme 2. Mononuclear Co111—peroxo complexes are relatively rare, but yellow trigonal bipyramidal complexes [Co(02)L2]+ (L = chelating phosphines dppe or dppp) have been characterized structurally where the 022 is bonded to the Co in the side-on r]2 form (Co—O 1.858(7) 1.881(4) A), with O—O stretching frequencies ( 870 cm-1) consistent with Coin-peroxo speciation.963... 

Even better results were obtained by Johnson et al. [24] with the Co compounds shown as Fig. 10. These were dissolved in appropriate solvents and immobilized into standard microporous membranes composed of nylon or PTFE. Oxygen permeabilities were as high as 3 x 10 8 sec-cm/(cm2-s-cmHg) with selectivity over nitrogen up to 20, leading to product purity up to 85%. 

In the fifth paper of this chapter on cathodes, an investigation of thin-film oxide-hydroxide electrodes containing Cr, Ni, and Co compounds was authored by N. Vlasenko et al. The thin-films were produced by electrochemical deposition from transition metal aqueous fluorine-containing electrolytes onto steel substrates. These thin-films were tested in Li coin cells. Electrochemical activity appears to scale with the amount of fluoride used in the deposition the larger concentration of fluoride in the bath, the greater the capacity. One Ni oxide-hydroxide film electrode showed greater than 175 mAh/g reversible capacity on the 50th cycle with excellent coulombic efficiency. 

Figure 4.101 Metal-carbon bond lengths Rmc for dative

Indirect Oxidation with Nickel (Ni) and Cobalt (Co) Compounds. .. 509... 

The properties of sulfur-rich, mononuclear Fe(CO) compounds as described by the group of Sellmann (Sellmann et al. 1996) alerted the hydrogenase workers that the protonation of a thiol ligand to Fe shifts the v(CO) in such compounds by about 40cm to higher frequency, whereas the redox potential of the Fe ion increases by 500-600 mV. 

Stabilizing the Support Oxide. Promoter elements can be added to the support oxide resulting in a decreased Co compound formation with the support oxide. This is illustrated in Figure 3A. More specifically, strategies should be followed to avoid the formation of either cobalt titanate, cobalt silicate or cobalt aluminate as a result of Co solid-state diffusion under reducing or regeneration conditions in the subsurface of these support oxides. Some transition metals, for example Zr or La, could act in such a way. 

Figure 3 The different modes of action of structural promoters in Co-based Fischer-Tropsch catalysis (a) structural promoter elements can lead to a decreased Co compound formation with the support oxide (b) structural promoter elements can act as an oxidic interface between the supported Co ...

A discussion of molecular orbital theory applied lo noble gas compounds wSI be found in Chapter 17, t GUespie. R. 1. In Noble Cos Compounds Hyman. H. H.. Ed. University of Chicago Chicago. 1963 p 333. 

On photolysis of the reduced or mixed valence enzyme, the 590 nm band of the a3-CO species disappears and a new band appears at 612 nm, due to the generation of five-coordinate cytochrome a2+. If dioxygen is present, and at a temperature higher than about —100 °C, then a new species (A) is formed, which cannot be photolyzed, and which is spectrally similar to the a3 -CO compound. It is probable that this involves 02 bound to the cytochrome a3, and does not involve bridging a3 and CuB. This species would approximate to oxyhemoglobin, and would involve some charge transfer to bound dioxygen. 

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