Cobalt structural data

Interpreting these results on a detailed molecular basis is difficult because we have at present no direct structural data proving the nature of the split Co(IIl/lI) voltammetry (which seems critical to the electrocatalytic efficacy). Experiments on the dissolved monomeric porphyrin, in CH-C solvent, reveal a strong tendency for association, especially for the tetra(o-aminophenyl)porphyrin. From this observation, we have speculated (3) that the split Co(III/II) wave may represent reactivity of non-associated (dimer ) and associated forms of the cobalt tetra(o-aminophenyl)porphyrins, and that these states play different roles in the dioxygen reduction chemistry. That dimeric cobalt porphyrins in particular can yield more efficient four electron dioxygen reduction pathways is well known (24). Our results suggest that efforts to incorporate more structurally well defined dimeric porphyrins into polymer films may be a worthwhile line of future research. 

The second sulfidocarbido cobalt cluster, SCo6C2(CO)14 (72), has a much more open structure (Fig. 37), and may be seen as two pyramidal Co3C units joined by two metal-metal bonds and a carbon-carbon bond, with a capping sulfur atom over the Co face. Detailed structural data have not yet been published. 

Table 78 Structural Data for Cobalt(lI)-Ether Complexes...

Both sulfide and disulfide are more commonly encountered as bridging ligands in cobalt clusters. There are few systematic syntheses. For example, [Co2(CO)g] reacts at room temperature with CS2 either neat or in the presence of hydrocarbon solvents to form [Co3(S)(CO)c,], [Co6(C)(S)2(CO)12] and at least three other sulfur-containing derivatives in addition to sulfur-free species such as [Co3(CXCO)9].979 Similarly, [Co2(CO)g] with elemental sulfur in hydrocarbon solvent gives [Co3(S)(CO)9], [Co4(S)2(CO)l0], [Co6(S)3(CO)6] and [Co6(S)4(CO) 4],980 with the product distribution dependent on the reaction conditions. Details of several cluster preparations are given in Table 79 and structural data in Table 80. 

A number of other mechanistic sequences are thought to occur in alkyne trimerizations mediated by other metal systems. Catalysts derived from Co2(CO)s follow a characteristic sequence of steps that involves exclusively dinuclear complexes (Scheme 26). The nature of the final (alkyne)3C02(CO)4 intermediate, a so-called flyover complex, is supported by both X-ray crystal structure data as well as its involvement in forming other products besides benzenes. These dinuclear cobalt systems are note-... 

The trans-tram forms occur in the crystals of cesium hexasulfide (5) and of (rans-dichloro-dien-cobalt(III) hexathionate monohydrate (107), and the ds-ds forms in the crystals of potassium barium hexathionate (102), these being the only compounds containing tetrasulfide groups for which structural data are available. 

The Cambridge Structural Database contains X-ray crystallographic data for all reported compounds and complexes of cobalt that contain carbon (see X-ray Crystallography. The November 2002 version of this database lists 10 403 structures containing cobalt, with the earliest, the Co(II) complex of the phthalocyaninate dianion, dating back to 1936. The Inorganic Crystal Structure Database" contains structural data for cobalt compounds... 

Selected structural data for /i-peroxo cobalt(III) complexes are included in Table 57. Orbital diagrams constructed for Co—O—O bonds in N4Co(02)CoN4 species show that irons bent bonds are the most stable and this is what is observed for the monobridged complexes. Dibridging forces the /i-peroxo group to adopt a skewed cis geometry except in cases (e.g. [(tren)Co(/i-tren,02)Co-... 

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