Other properties of cobalt.
This chapter aims to collect and summarize the chemical properties of cobalt and some new cobalt compounds. It deals with the progress of cobalt chemistry. Cobalt has been substantial in both chemical reactions and within many compounds. Some of them are heterocyclic reactions, cobalt-based catalyst and cobalamin. Also, it discusses variety of applications of cobalt in a wide range of areas and toxicity of cobalt. The studies carried out in this area so far have enabled and will be continued to be responsible for producing unknown and difficult reactions. This survey of the recent literature illustrates the fact that many different approaches on cobalt and new cobalt compounds are being used in many different areas.
- cobalt compounds
- areas of usage
The word cobalt is derived from the sixteenth century German term kobold. Glass, glazes and blue dyes for pottery were the oldest known uses of cobalt. For instance, cobalt compounds were used to dyeing pottery by Egyptians and Babylonians in 1450BC. Cobalt was set apart from copper ore by Swedish chemist Georg Brandt in 1735. After 1900, a new corrosion resistant alloy was invented, which is referred to as Stellite. Furthermore, aluminum-nickel-cobalt (
By 2000, scientists had carried out lots of experiments related to the synthesis of new cobalt compounds, examination of antibacterial properties of cobalt compounds and cobalt-catalysed reactions. For example, Kumar and Garg synthesized cobalt(II) complexes of tetradentate Schiff bases of the type .
Nowadays, cobalt and cobalt compounds possess a variety of applications from industry to medicine. This is because of its unique properties such as a high-melting point (1493°C) and retaining its strength to a higher temperature, being ferromagnetic with high thermostability and multivalent. Cobalt is one of the abundant metals in the Earth. Global reserves of cobalt are approximately around 7 million tons .
This chapter aims to collect and summarize the chemical properties of cobalt and some new cobalt compounds. The studies carried out in this area so far have enabled and will be continued to be responsible for producing unknown and difficult reactions. This survey of the recent literature illustrates the fact that many different approaches on cobalt and new cobalt compounds are being used in many different areas.
In order to briefly discuss about cobalt chemistry in this section, we begin with cobalt electron configuration. Cobalt has the chemical configuration [
|Atomic number||27||Atomic mass||58.93|
|Electron Distribution||[Ar]3d7 4s2||Oxidation Number||+2,+3|
|Melting Point||1495°C||Boiling Point||2870°C|
|Density||8.9 g/cm3||Atomic Volume||6.7|
|Ionization Energy||757.6 kJ/mol|
Cobalt has some inorganic compounds and complexes. Some chemical and physical properties of cobalt and several inorganic cobalt compounds are mentioned in the following statements.
Dilute sulphuric or hydrochloric acid dissolves slowly, but nitric acid rapidly dissolves and produces the cobalt-II ions 
Cobalt gives cobalt(II) chloride by dissolving in dilute hydrochloric acid .
It is insoluble because it acquires passivity in concentrated nitrate and sulphuric acid .
Another oxidation number of cobalt is +3. But this ion can only be found in the complex. Bare cobalt releases oxygen from acidic and neutral environment. All cobalt oxides dissolve in hydrochloric acid .
Cobalt generally forms cobalt(II) and cobalt(III) compounds, but there are cobalt compounds, which have 4 +, 1 +, 0, 1− oxidation states . It is more stable than those compounds which consist of cobalt-III ions. In general, cobalt-II compounds dissolve in water; however,
It is known that all common cobalt compounds have octahedrally coordinated to nitrogen or oxygen ions, all of which include three cobalt ions, two of which are 3+ and one of which is 2+, similar to the title compound.
Cobalt is found together with iron, copper, nickel, silver and arsenic in nature. Cobalt closely resembles nickel so that they are being identified as “twins.” Although cobalt is used in practice to plate iron, doing alloy is the most significant practice of cobalt. Important cobalt alloys and its uses are summarized in Table 2.
|Alloy name||Percentage composition||Features||Places used|
|Stellite||50–60 Co, 30 Cr,20 W,Mn, C||Hard and pourable||Cutting and drilling tools and mould|
|Vitallium||65 Co, 25 Cr, 5Mo||Resistant to wear and tear||Gas turbine wings|
|Magnet steel||35–60 Co, 10–25 Ni,Fe||Can be magnetized||Magnet|
The most known minerals are linnaeite,
Cobalt compounds which give blue color to glasses can also be made radioactive and can be used for treatment of some cancers. Further, it is used for the treatment of deep-rooted tumors. This shows that radioactive cobalt can be used as a tracer .
It is commonly known that salts and complexes of cobalt are catalysts for the selective oxidation of alkanes and selective epoxidation of alkenes. Scientists have performed several experiments on these catalysts. Several of them are discussed in this chapter .
In order to make liquid fuel, cobalt catalyst is used in the Fischer-Tropsch process. Also, cobalt and molybdenum are utilized as a catalyst in hydrodesulphurization of petroleum. These processes make use of refining of liquid fuels .
The chemistry of cobalt complexes has attracted a lot of attention in recent years on account of their applications, among others, in biological systems such as antimicrobial agents and antibacterial agents.
To design novel drugs, medicinal chemistry has benefited from the properties of metal ions. Hence, this has caused to have clinical application of chemotherapeutic agents for cancer treatment, such as cisplatin .
Some of these works were mentioned as follows. In 1952, the first biological activity of cobalt compounds was acquainted where cobalt(III) compounds of bidentate mustard move as if it were hypoxia selective agents .
Bauer and Drinkard prepared and identified several new cobalt(III) complex compounds of easily oxidized ligands. These were salts of cobalt amines, inner charge complexes, and a variety of cobaltates. The structural formula was
It is commonly known that salts and complexes of cobalt are catalysts for the selective oxidation of alkanes and selective epoxidation of alkenes. Scientists have carried out lots of examination on these catalysts. Several of them are
Cobalt studies are still continued due to the fact that they have a wide variety of functions and many applications, especially in pharmaceutical technology.
2. Used places
Cobalt has many applications in a wide range of areas. A solution of
It is commonly known that salts and complexes of cobalt are catalysts for the selective oxidation of alkanes and selective epoxidation of alkenes. Scientists have carried out lot of on these catalysts. Several of them are
Exciting results have been obtained from these studies over the last two decades. For example, it was found that there was redox activity of quinone ligands and potential for forming compounds. These formed compounds may involve in a number of electronic states due to the combined electrochemical activity of the cobalt ion and one or more quinone ligands .
Cobalt compounds can be made use of treatment of some cancers .
Magnetic, wear-resistant, and high-strength alloys are chiefly made by cobalt metal. It is suitable for applications such as desulphurization of hydrocarbons, the removal of nitrous oxide, and the emerging technology of converting natural gas to liquid hydrocarbons due to its unique catalytic properties. Because of allowing manufacture of highly effective cutting tools, it is also suitable for base industry application. It is used in both gas turbines and aggressive working setting owing to high-temperature resistance, hardness and wear characteristics of cobalt while alloyed with other metals. It may be also contributed to improve the operating efficiency by means of durability and wear capacity .
Besides, cobalt is generated a significant part of vitamin B12 in biochemistry. Vitamin B12 is a
Cobalt catalysts are practiced in many reactions, which are the synthesis of heterocycles. One of them was cobalt-catalyzed oxidative free-radical cyclization of alkyl bromides in 1986 .
Another example of these reactions is 3,
In order to make liquid fuel, cobalt catalyst is used in the Fischer-Tropsch process. Also, cobalt and molybdenum are utilized as a catalyst in hydrodesulphurization of petroleum. The process made use of refining of liquid fuels .
In biochemistry, Vitamin B12 ranked sixth coordination position of Co(III) that is included cyanide ion and so it has another name, cyanocobalamin. Cobalamin complex is joined to 5′
Vitamin B12 is indispensable for advanced creatures, but it is not vital for plants. It can only be synthesized by certain bacteria. The living creatures obtain it through the food. Vitamin B12 is digested in the ileum by a mucopolysaccharide, which is present in the gastric juice. If vitamin B12 is lacking or not digested, various diseases come into play. One of them is pernicious anemia. There is no absorption of cobalamin in patients with parenteral anemia. This is shown that it is vital for synthesis of hemoglobin. Besides, all of these indicate the biochemical significance of cobalt .
3. Some common cobalt compounds
Cobalt II salts are red in the case of complex-ion, that is, solvated with water, and it is dark blue when dehydrated. Invisible ink is made using this feature. If the diluted
Besides, it is used to say how much moisture present in air. When there is humidity in weather, paper becomes pink .
3.1. Cobalt II sulfate,
CoSO4.7 H2 O
It is dark red that gives double salts with alkali sulfates and is a form of monoclinic prisms .
3.2. Cobalt nitrate,
Co( NO3).6 H2 O
It is separated from water in the form of red monochlorine crystals. If
Co2( SO4)3.18 H2 O
It is obtained by anodic oxidation of
4. Synthesized new cobalt compounds
Cobalt was investigated by many scientists over years. These works ended up with many cobalt compounds. For example, Kumar and Garg synthesized cobalt(II) complexes of tetradentate Schiff bases of the type
The chemistry of cobalt complexes has attracted a lot of attention in recent years on account of their applications, among others, in biological systems such as antimicrobial agents and antibacterial agents (DNA studies and cytotoxicity studies) .
Some of this works were mentioned as follows. In 1952, the first biological activity of cobalt compounds was acquainted where cobalt(III) compounds of bidentate mustard move as if it were hypoxia selective agents. Then, some compounds demonstrated significant activity against bacterial strains and against leukemia and lymphoma cell lines . Afterward, lots of studies were carried out on anti-microbial, anti-fungal and anti-oxidant activities of cobalt compounds .
By 1960, several new cobalt(III) complex compounds of easily oxidized ligands were prepared and identified. These were salts of cobalt amines, inner charge complexes and a variety of cobaltates. The structural formula was
It was reported that
It was demonstrated that a complex form of cobalt(III) was an active catalyst for the selective oxidation of alkylaromatics using air. The air was used as the source of oxygen in the absence of solvent .
Park et al. reported the synthesis of “solid solution” and “core-shell” types of well-defined
When pure metals like Fe, Co and Ni and their metal alloys utilized in magnetism, it is difficult to use them because of their oxidation in air. Moreover, this difficulty increases when the particle size gets smaller. So, the stability of particle enhances with a variety of methods. One of them is deposition of insulating shells on the nanoparticles surface. A procedure that leads to air-stable Co nanoparticles was carried out by Gedanken et al. . They pretended that the formation of a carbon shell on the nanoparticle surface increases stability. But, acquired particles were not uniform .
Kobayashi et al. informed that it was a procedure, which allows the preparation of Co nanoparticles of various sizes in aqueous solution and their coating with well-defined silica shells. They found an easy chemical method for the synthesis and stabilization of magnetic and amorphous Co nanoparticles. These Co nanoparticles were surrounded by homogeneous shells of silica. This novel type of composite magnetic nanoparticles has potential applications, both in the field of ferrofluids and in magnetic storage media. The controlled assembly of
The formation mechanism of the tubular structure of
In vitro antimicrobial activity of cobalt(II) complexes was studied. These ligands were [
It was reported that synthesis of cobalt nanoparticles using a polymeric microfluidic reactor by the reduction of
Ingersoll et al. carried out nickel-cobalt-boride (
By 2008, cobalt nanoparticles using thermal decomposition of [
Bruijnincx and Sadler investigated the design of modernist metal-based anticancer drugs that include recent literature. Many novel chances for anti-cancer drugs were gained low systemic toxicity and ability of coming from the top of the drug resistance. In their work was been presented with different examples of promising offer. These studies caused expansion toolbox of medical inorganic chemistry .
It had been studied with three species of bacteria, in order to found the activity of the schiff base and their complexes. In this work, it was found best results with diameters (30 mm), due to the inclusion of Co(II) ion. This was shown that the complexes have more antibacterial activities than the free Schiff bases .
Kumar and Chandra synthesized cobalt compounds that exhibit significant antifungal activity .
Pannu et al. synthesized [
The research was carried out in cobalt catalysis and they obtained cost-effective catalysts and milder conditions for existing C−H functionalization. Their studies also paved the way for unrivaled chemical transformations. They found two answers for two questions in this study. First, low-valent cobalt catalysts may imitate the reactivity of noble transition metal catalysts to C−H activation. Second, in C − H functionalization, cobalt catalysts may present matchless reactivity and selectivity and these properties provide a way for undergoing mysterious and hard synthesis transformations, up to now. Given examples were branched-selective hydroarylation of styrenes, ortho-alkylation of aryl imines with secondary alkyl halides and migratory arylzincation of alkynes. Their work brought out novel difficulties and possibilities. It was necessary to fully understand the reaction mechanism and the nature of the catalyst due to further growth in this area .
Gaëlle et al. synthesized and investigated two complexes, a cobalt(II) complex [
|Co(NO3)26H20||O-Phen||||Complex 1||Complex 2||Gentamycin||Nystatin|
Both of them may stand for decent nominees as an antibacterial (1) and antifungal agent (2). However, Gaëlle et al. continued the relevant works .
Three new cobalt(II) coordination compounds were reported (i.e.,
In 2016, three homospin compounds of chain structures that were linked to pentagonal bipyramidal Co(II) units were synthesized (Figure 3). Moreover, this work demonstrated the preparation of higher dimensional coordination polymers .
Cody et al. synthesized two new metal thiophosphate anions, [
Two new mono- and dinuclear Co(II) complexes namely
Also, cobalt is used as a catalyst in some reactions. For instance, cobalt-based catalysts are essential in reactions involving heterocycle synthesis. Adam et al. carried out catalytic hydrogenation of nitriles to primary amines. They used
Ko et al. carried out the preparation of hollow cobalt oxide and cobalt selenide microspheres and their Na-ion storage properties. Hollow cobalt selenide microspheres were classed with the hollow cobalt oxide microspheres. Hence, it was applied as an anode material for NIBs. Selenide microspheres showed high initial discharge capacity and high initial Coulombic efficiency as well as good cycling and rate performances for Na-ion storage. Also, they had structures that improve electrochemical properties by means of optimizing the electrolyte system used for Na-ion storage. On the other hand, hollow cobalt oxide microspheres were favorable from the point of their high initial capacity and low voltages for Na-ion storage as anode material for NIBs. They had leveragable cycling and rate performances. So, both of these microspheres were act as a promising anode material for NIBs .
Mondal et al. prepared mixed
It was made with fabrication of Ni NWs decorated with Co NPs by using two-step etching and deposition technique in 2016. This study showed that nanoparticles dispersed on the surface of nanoparticles as shown in Figure 6. They declared in this study that this technique has been used for the first time in order to manufacture nickel nanowires which are adorned with cobalt nanoparticles .
Montazerozohori et al. synthesized a new nanostructured cobalt(II) bromide complex with a bidentate Schiff base ligand. Particles’ size of complex in nanodimension size by XRD and SEM analyses is shown in Figures 7 and 8 .
It was shown, in another work in 2017, a novel dry coating technology for Co/Al2O3 catalyst synthesis without solvents and heating treatment. The dry-coated catalysts were presented as comparable to conventional chemical impregnated catalysts. Figure 9 shows a spherical shape of Co/Al2O3 .
Przyojski et al. synthesized two new complexes of cobalt(II) with 7-azaindole. They have Co(II) in a distorted tetrahedral environment. Asymmetric units of complexes are shown in Figures 10 and 11 .
Four novel complexes [
Hassanzadeh et al. investigated the cobalt Schiff base complex-modified CPE containing cationic surfactant. This complex could increase resolution and selectivity of voltammetric responses of DA and AA. Also, it was challenging to distinguish the voltammetric peaks of DA and AA. It obtained the better of resolution than previous reported works. This makes it suitable for simultaneous detection of these compounds. Moreover, it was simple preparation, acceptable selectivity and sensitivity, had low-detection limit and reproducibility. All of them made the prepared system very effective in manufacturing .
Studies on cobalt are continuing due to the fact that they have a wide variety of functions and many applications, especially in health sector. Unfortunately, cobalt derivatives have not been studied as pharmaceutical, yet. Up to now, the only cobalt-based drug is Doxovir that is Co(III) Schiff base complex and its mechanism is not also completely understood .
5. Toxicity of cobalt
Physical contact with cobalt is not the only way to expose to a substance. You may be exposed by lot of routes such as breathing, eating or drinking the substance, or by skin contact. Metal poisonings occur because of different reasons. For example, cobalt toxicity depends on oral intake and inhalation. Cobalt exposure related to using vitamin B12 is considered as there is low toxicity due to fast rate of renal excretion and limited oral intake. Mostly, absorbed cobalt (50–88%) eliminated by renal excretion rest by feces.
Just as other metals, cobalt is also a multiple organ poison.
It is brought to attention that cobalt may inhibit aerobic metabolism with increasing glycolysis while
Cobalt poisoning causes gastrointestinal distress and heart failure. Chelating agents are used in the treatment of those poisonings .
Cobalt also prevents Krebs cycle by generating reduced α-lipoic acid. Besides, cobalt salts inhibit dihydrolipoic acid by forming complex with dihydrolipoic acid sulfhydryl groups.
Result of this reaction, it is not enough pyruvate convert to acetyl co-A and α-ketoglutarate convert to succinyl-coA.
Moreover, CoCl2 inhibit tryrosineiodinase enzyme. This causes the reduction of triiodothyronine (T3) and thyroxine (T4) .
In this chapter, chemical properties of cobalt and some new cobalt compounds were discussed. It deals with the progress of cobalt chemistry. Cobalt is substantial in both chemical reactions and within many compounds. Some of them are heterocycle reactions, cobalt-based catalyst and cobalamin. Cobalt studies are continuing due to the fact that they have a wide variety of functions and many applications, especially in pharmaceutical technology. These studies caused appearance of medicinal bioorganometallic chemistry and expanding of medical inorganic chemistry. The studies so far in this area carried out have enabled producing unknown and difficult reactions and they will be continued to be responsible for them. This survey of the recent literature illustrates the fact that many different approaches on cobalt and new cobalt compounds are being used in many different areas. For example, one of them is that many different new creative approaches are being taken toward the design of innovative metal-based anticancer drugs.