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Cobalt III Complexes


Since vitamin B12 was isolated in the year 1948 and its anti-pernicious anaemia factor interests in the vitamin especially the model complexes as far as sustaining them is concerned, the phase that occurred second from the year 1948 to 1955 involved the development of methods was all about the development of methods that were used for the process of large scale production of vitamin B12 by techniques of fermentation that were passed through the processes of screening as well as the selection of micro-organisms. The third phase that occurred between the year 1950 and 1962 involved the recognition pertaining vitamin B12 as belonging to corrinoid group that is found in nature as well as finding out the answer to the question is why corrinoids occur in nature. The latter is as so following the pioneer works of on vitamin b12 by Bernhauer and the co-workers in the establishment of what they so called the "co enzymes" form of the corrinoid possessed organ ligands. Different ligands that are chelating come to an emergence whereby the properties as well as the reactions were now able to be investigated as well as employed to the model of vitamin B12.

A ligand can be described as an ion or a molecule whose purposes is to bind to a central metal on so as to form a co-ordination complex. The latter involves the donation of one or even more of the ligands electron pairs. The ligands can bind through one or two or even more atoms so as to form linkages that are isomer like thiocyanate. Some ligands have been found out to be better than others by having rates o equilibrium that is relatively faster than the others.


Different existent studies on the chemistry that surrounds the electron transfer reaction of the cobalt (III) complexes have received levels of attention that are high from the scientific community for many decades due to the relevance that they play when it comes to the red ox processes that are existent in the biological process and are day in day out promising to be agents for anti-tumours, anti-parasitic, anti-microbial activities as well as Aanthelmintics.

The surfactants are often used in the process of formulation of pesticides as well as herbicides. They have also found wide ranges of applications when it comes to their properties such as solubilisation and detergency. The Cobalt (III) ion comes to form many stable complexes due to the fact that it is inert in nature which therefore means that it is capable of exhibiting different or various types of isomerism. Cobalt complexes are less susceptible to the process of hydrolysis despite the fact that limited hydrolysis may occur so as to lead to poly nuclear Cobaltamminnes that have the bridging OH- groups.

Cobalt (III) non-organ metallicmodel comprises of complexes of the vitamin b12 that posse's diphenylglyoxime (H2dpg) has been prepared with various axial nitrogen or even phosphorous bases as halides and ligands as well as pseudo halides as anions. The complexes are characterized by microanalyses, room temperature, infrared spectra as well as thermal gravimetric analysis. All the complexes are found out to be diamagnetic which therefore means that they are octahedral d6 Co (III) complexes. All the complexes that are decomposed below 400 degrees Celsius mark and show one major TGA profile below the 400 degree Celsius mark by corresponding to the loss that occurs which is of one major component which can either be the base or the diphenylglyoxime. The profile that exists between the 400 and 800 degrees Celsius is poorly defining making the percentage residue not be able to be calculated. The Co (II) /Co (I) couples were found out to be reversible for most parts of the complexes whereas Co (III) /Co (II) appeared to be either quasi reversible or irreversible which means that they had to be considered to be possible models of vitamin B12.

The NMR spectroscopy was used in the process of determining isomerism of other related products. The symmetrical Cis isomer was first reported to be of the colour purple whereas the Trans isomer was reported to be of the colour green. The second legend as studied was found out to only be adopting the Trans configuration. The complexes were furthermore found out to be preferential in the form of unsymmetrical cis isomer when they were isolated just as the din trite and the oxalate species. The proton NMR did in fact help in the establishment of the 3 isomers was found out to be helping in the identification of the 3 isomers. Just as a symmetrical cis or a Tran's isomer would, the methyl groups the methyl groups have been equivalent and have also contributed to single signals. Despite the later fats, the two distinct signals have been observed for the purposes of the din trite as well as the oxalate species indicate the formation of isomers that are unsymmetrical.

Complexes of the third ligand that are red in colour were established as nitro salts and therefore the results that occurred of the NMR measurements indicated that the ligand coordinated so as to form the only unsymmetrical is isomers. The effect of placing the methyl groups upon stereochemistry was clearly illustrated by these studies. The placement of the methyl groups in the 2 and 9 portions yielded little effect upon the isomers that were preferred whereas when the isomers were placed in the 3,8 as well as 5.,6 positions, they were found out to be yielding isomers that were unsymmetrical.

Cobaloximes were synthesized as well as characterized by elemental analysis whereby the melting points as well as the elemental analysis, solubility, melting points, room temperature and the magnetic susceptibility measurements as well as the cyclic volumes showed that the complexes melted then decomposed at 220 degrees Celsius with the exception of a few, many of them happened to dissolve in the coordinating organic complexes through the n atom of the oxime group each and every ligand. The complexes also happen to be non-electrolytes in organic solvents. The spectra of the IR indicted that the complexes are low -spin d6 octahedral. The electro chemical on some of the existing complexes showed that some of the complexes underwent reversible oxidation reductions therefore making them viable models for the vitamin B12. Many varieties of the structures have ended up being proposed or the complexes.

The synthesis as well as the characterization of the organ metallic and the inorganic cobalt (III) compounds is reported where the dpgH represents the diphenylglyoximate mono anion. Their structure as well as the stereoscopic properties are studied as well as compared with those of the previously reported analogous compounds that contain g dimethylglioximato(-1) or the N2,N2'-propanediylbis(2,3-butanedione, 2-imine-3-oxime) as equatorial ligands. The 1H- NMR chemical tends to shift of the axial R group in diphenylglyoximato compounds that can be estimated accurately room those of the glyoximatoor the dimethylglyoximato analogous with the allowance of the detecting of the electro cis-effects. The first x ray crystal structure as reported on organometallic bis cobalt (III) compound is reported. The cobalt carbon length in the latter type o complex seems not to be able to be sensitive when it comes to the changes in the equatorial ligands.

Some certain Schiff base complexes that have been proposed as models are also seen to be reported by Johnson and Dolphin. The cobalt polyphyrin could however not be reduced to the form of Co (II) under the conditions whereby we see that B12s was obtained. In all the models of complexes we see that the in plane ligands, do not get displaced and the variations that occur involving the changes in the axial ligands (Dolphin, 495).

As of recent times, the demonstration that the inorganic models that involved the dimethylglyoxime23 as well as cyclohexanedioneglyoxime24 could indeed undergo some of the reversible re- dox process and that they were therefore established as the models that were viable for vitamin B12. In this hypothesis, we can report that the results that were concluded as per our studies on the synthesis of as well as the characterization of numbers of new Co(III) diphenylglyoximato complexes makes us able to examine whether the placement of the methyl group in Hdmg or the C6H12 which is in the Hyclodmg group with the phenyl ring would come to show any influence that was measurable on the stereo chemical as well as the re -dox properties of the complexes which is with the incorporation of the bases that were bulky in the axial positions with one anticipating the changes that were possible when it comes to possible changes in the establishment of the stochiometry changes of the complexes (Ndahi, 6).

Since the time when the isolation of vitamin B12 in the year 1948 along the establishment of the "anti-pernicious anaemia factor", the interests in the vitamin especially the model complexes have been sustained since the second phase from 1948 to 1955 involved the development of the methods that are used in the large scale production of vitamin B12 through the techniques of fermentation which involve the process of screening and selection of micro-organism. The third phase establishes the answer to the question which corrinoids are found in nature whereby we see the answer is established which corrinoids are found in nature.

The process of oxidation of cobalt (II) to cobalt (III) in the series comes to be more difficult than in the cyclohexanedioneglyoximato24 and dimethylglyoximato23 complexes. The complete oxidation was found out to be requiring bubbling oxygen through the reaction mixture for a minimum of 12 to 24 hours with 1-3 hours being for the Hdmg and Hcyclodmg and some cases leaving the reaction mixtures complexes for days before the process of filtering.


A conclusion can be arrived at that the complexes are octahedral as well as diamagnetic and non-electrolytes with the evidence being based on the reversible Co (II)/Co(I) couples as well as the pseudo-irreversible as well as reversible couples that support our propositions on some of the complexes that could be established as vitamin b12 mimics. The irreversible nature of the couples of Co (III) /Co (II) could have been of an origin that was chemical whereas the halides are oxidized by Co (III) ion. The identity of the species of the PF4 appears to be dependent on the donor atoms of the axial bases. The bases that are bi dentate and contain the donor N atoms have the appearance of facilitating the reduction of P (V) to P (IV) in the PF-6 with such devocalizations not been favoured in the Phospine axial bases

Some of the things that I have learnt on the topic include the importance's that arise from the organ metallic's and the role that they play in the developing of the vitamin B12 molecule which is vital in the many enzymatic transformations based on the remarkable properties of these classes of compounds which lead to a new area of medical research.

Works Cited

Dolphin D. and Johnson A.W. (1965). Alkyl-cobalt (III) complexes of etioporphyrin

Ndahi N.P. and Kolawole G.A. (2004). Cobalt (III) complexes of cyclohexanedionedioxime

Models for vitamin B12. Ultra Sci. Phys. Sci

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