Cobalt synthetic structures

Calligaris, M., Nardin, G., Randaccio, L., and Ripamonti, A. (1970) Structural aspects of the synthetic oxygen-carrier N,N -ethylenebis (salicylideneiminato)cobalt(Il) Structure of the addition compound with oxygen containing dimethylformamide", J. Chem. Soc. A, 1069-1074. 

Alexopoulou KI, et al. Mononuclear anionic octahedral cobalt(III) complexes based on A/-salicylidene-o-aminophenol and its derivatives synthetic, structural and spectroscopic studies. Spectrochim Acta Mol Biomol Spectrosc 2015 136(Part A) 122-30. 

With sp bond angles calculated to be around 162°, macrocycle 131 would be highly strained and was therefore expected to be quite reactive [79]. The octa-cobalt complex 132, on the other hand, should be readily isolable. Indeed, 132 was prepared easily from 133 in five steps, and was isolated as stable, deep maroon crystals (Scheme 30). All spectroscopic data supported formation of the strain-free dimeric structure. Unfortunately, all attempts to liberate 132 from the cobalt units led only to insoluble materials. Diederich et al. observed similar problems when trying to prepare the cyclocarbons [5c]. Whether the failure to prepare these two classes of macrocycles is due to the extreme reactivity of the distorted polyyne moiety or to the lack of a viable synthetic route is not certain. Thus, isolation and characterization of smaller bent hexatriyne- and octatetrayne-containing systems is an important goal that should help answer these questions. 

In a different approach three different structurally defined aza-crown ethers were treated with 10 different metal salts in a spatially addressable format in a 96-well microtiter plate, producing 40 catalysts, which were tested in the hydrolysis of /xnitrophenol esters.32 A plate reader was used to assess catalyst activity. A cobalt complex turned out to be the best catalyst. Higher diversity is potentially possible, but this would require an efficient synthetic strategy. This research was extended to include lanthanide-based catalysts in the hydrolysis of phospho-esters of DNA.33... 

At present, synthetic routes to more than 40 metal complexes other than the copper complex are known. Apart from a cobalt phthalocyanine pigment (P.B.75) which was introduced to the market just recently, none of the resulting products, however, has stimulated commercial interest as a pigment. Nickel complexes, however, are found in reactive dyes, while cobalt complexes of this basic structure are employed as developing dyes. 

The resulting heterocycles can be structurally manipulated, e.g., reduced or desilylated either during complexation or after demetallation. Another possibility consists in using the primary products, obtained by the cobalt-mediated cycloaddition, as synthetic intermediates for further catalytic transformations. Indole derivatives have been cocyclized at cpCo to give 4a,9a-dihydro-9 f-carbazoles or, after oxidation, precursors for strychnine (63T247 86JA2091 87MI7) [Eq.(36)]. 

Table 1 shows the properties of smectite-type materials prepared. Smectite materials prepared at lower pH had fewer sodium ions, higher surface areas, and larger pore volumes for a series of samples containing the same divalent cation species (nickel and cobalt) in the octahedral sheet. The adsorption of methylene blue on all the synthetic smectites shows that the smectite fragments are negatively charged. The Si M ratios of synthetic smectites were about 8 6, indicating that most of divalent cations exist in octahedral layers and small amount of divalent cations would exist as hydroxide or oxide cluster in smectite materials. However, the amounts of the hydroxide or oxide cluster were small, because only smectite structures were observed in XRD patterns and EXAFS Fourier transforms of synthetic smectites calcined at 873 K. 

It is apparent from most of the examples previously described that the most common formal oxidation state found for the Group 14 element is E(IV) (E = Ge, Sn, Pb). Relatively few examples of divalent germanium, tin, or lead complexes have been described, and of these, many are not well characterized. Cobalt-containing compounds are no exception in this regard and there appears to be only one report in the literature that describes a species of this type, viz. [Ge Co(CO)4 2], 67, although the precise structure of this complex is unknown (77). Two main synthetic routes are described, Eqs. (4) and (S), the starting complex in the latter reaction being... 

In the simplest case, reaction of a primary monoamine via a two-fold Michael reaction with acrylonitrile (bis-cyanoethylation) led to the dinitrile (Fig. 1.1). Subsequent reduction of the two nitrile functions - by hydrogenation with sodium borohydride in the presence of cobalt(II) ions - afforded the corresponding terminal diamine. Repetition (iteration) of this synthetic sequence, consisting in Michael addition followed by reduction, provided the first - structurally variable - access to regularly branched, many-armed molecules. 

The X-ray structure refinement of a synthetic Mg-Co2+ olivine (Ghose and Wan, 1974 Ghose et al., 1975) show that Co2+ ions also favour the Ml sites. The Xddata plotted in fig. 6.3 indicate that cobalt is less strongly enriched than Ni2+ ions in the Ml sites. The X-ray structure refinements (Ghose et al., 1975) and Kd data plotted in fig. 6.3 show that Zn2+ ions also favour the olivine Ml sites. 

The coordination chemistry of cobalt can be summed up in three words synthesis, structure and reactivity, with synthesis being the most important because it comes first. This chapter concentrates on synthetic aspects and its aim is to provide the reader with starting points to the preparation of cobalt complexes in addition to surveying their chemistry. 

Cobalt(III)-carbonato complexes provide a very useful starting point for the preparation of other cobalt(III) complexes so that high yield synthetic methods are of great practical importance. Table 67 lists preparations for the major structural types (241 >-(244) and variations for substituted or related ligand systems are based on these. Recent reviews covering the wider aspects of transition metal carbonates are available.872 874... 

The unmatched complex structure of the low-molecular weight natural product vitamin Bn posed a challenge to synthetic chemistry, which was met in the early 1970s by Eschemnoser and by Woodward and their coworkers. The biosynthesis of the structure of natural cobalt-corrins is no less intricate and facets of its pathways still remain to be uncovered (see section 2.3). 

Additionally, the L. innocua ferritin-like protein served as a template for the controlled mineralization of two cobalt oxide phases Co(0)OH and C03O4 under two reaction temperatures of 23° and 65 °C, respectively. Substantial differences in crystallinity of the cobalt mineral core was observed between the two synthetic routes. The mineralization reaction carried out at higher temperatures yielded more crystalline nanomaterials, while the low-temperature synthesis tended toward amorphous material. The high crystallinity obtained at higher temperatures is most likely due to removal of structural waters present in the protein cavity and the surpassed energy barrier of nucleation at 65 °C. ... 

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