Cobalt complexes, organic derivatives

The second structural type found for organometallic cobalt porphyrins contains an organic fragment bridged between the cobalt and one pyrrolic nitrogen. Cobalt complexes of N-alkyl- or N-arylporphyrins arc well established (but will not be specifically addressed here). The bridged complexes are derivatives of these where the N-alkyl group also forms a cr-bond to cobalt. They are also related to the axially... 

D. Gatteschi, C. Zanchini Spectral-Structural Correlations in High-Spin Cobalt (II) Complexes. - A. Tressaud, J.-M. Dance Relationships Between Structure and Low-Dimensional Magnetism in Fluorides. - V.KJain, R.Bohra, R.C.Mehrotra Structure and Bonding in Organic Derivatives of Antimony (V). 

Now, returning to the structure of the cobalt complex, we have derived the rankings as shown in Figure 7. One might agree that these are highly stylized and schematic procedures and the formalism leads to some results not intuitively anticipated. However, at Chemical Abstracts Service, we have accumulated a vast amount of experience with the CIP system with hundreds of thousands of compounds, both organic and coordination, and we find very few cases in which the CIP formalism completely breaks down. 

Until recently all known tr-organic derivatives of trivalent cobalt included either a planar tetradentate (or bis-bidentate) ligand or several specific monodentate or bidentate strong-field ligands, such as cyanide ion and 2,2 -bipyridine. The new type of organocobalt(III) complexes at issue, [1]+X, were reported1 in 1981. They contain as ligands,... 

Table 8 shows cobalt complexes derived from organic isothiocyanates. 

Most living organisms depend on catalysis by the transition element cobalt (1). The biological relevance of cobalt is due, mainly, to vitamin B12 derivatives (2,3), also known as cobalt corrinoids (4). In exceptional cases, enzymes may contain natural noncorrinoid cobalt ions (5), and structural Zn centers have been reconstituted with Co (and other divalent metal) ions, without significant loss of activity (1,4). Only some microorganisms are able to produce B12 derivatives naturally (6,7). Cobalt complexes similar to vitamin B12 (1) may have had fundamental roles in early forms of life on earth (1,8). 

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