The manganese is a chemical element that consists of a transition metal, represented by the symbol Mn, and whose atomic number is 25. Its name is due to black magnesia, nowadays the mineral pyrolusite, which was studied in Magnesia, a region of Greece.
It is the twelfth most abundant element in the earth's crust, found in a variety of minerals as ions with different oxidation states. Of all the chemical elements, manganese is distinguished by being present in its compounds with many oxidation states, of which +2 and +7 are the most common..
In its pure and metallic form it does not have many applications. However, it can be added to steel as one of the main additives to make it stainless. Thus, its history is closely related to that of iron; even though its compounds have been present in cave paintings and ancient glass.
Its compounds find applications within batteries, analytical methods, catalysts, organic oxidations, fertilizers, staining of glasses and ceramics, dryers and nutritional supplements to meet the biological demand for manganese in our bodies..
Also, manganese compounds are very colorful; regardless of whether there are interactions with inorganic or organic species (organomanganese). Their colors depend on the number or state of oxidation, being the +7 most representative in the oxidizing and antimicrobial agent KMnO4.
In addition to the above environmental uses of manganese, its nanoparticles and organic metal frameworks are options for developing catalysts, adsorbent solids, and electronic device materials..
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The beginnings of manganese, like that of many other metals, are associated with those of its most abundant mineral; in this case, pyrolusite, MnOtwo, which they called black magnesia, for its color and because it was collected in Magnesia, Greece. Its black color was even used in French cave paintings.
Its first name was Manganese, given by Michele Mercati, and then it changed to Manganese. The MnOtwo It was also used to discolor glass and, according to certain investigations, it has been found in the swords of the Spartans, who by then were already making their own steels.
Manganese was admired for the colors of its compounds, but it was not until 1771 that the Swiss chemist Carl Wilhelm proposed its existence as a chemical element.
Later, in 1774, Johan Gottlieb Gahn succeeded in reducing the MnOtwo to metallic manganese using mineral coal; currently reduced with aluminum or transformed to its sulfate salt, MgSO4, which ends up being electrolyzed.
In the 19th century, manganese acquired its enormous commercial value when it was shown that it improved the strength of steel without altering its malleability, producing ferromanganese. Likewise, the MnOtwo found use as a cathode material in zinc-carbon and alkaline batteries.
Metallic silver color.
54,938 u
25
1,246 ºC
2,061 ºC
-At room temperature: 7.21 g / mL.
-At melting point (liquid): 5.95 g / mL
12.91 kJ / mol
221 kJ / mol
26.32 J / (mol K)
1.55 on the Pauling scale
First level: 717.3 kJ / mol.
Second level: 2,150.9 kJ / mol.
Third level: 3,348 kJ / mol.
Empirical 127 pm
7.81 W / (m K)
1.44 µΩ · m at 20 ºC
Paramagnetic, it is weakly attracted by an electric field.
6.0 on the Mohs scale
Manganese is less electronegative than its closest neighbors on the periodic table, making it less reactive. However, it can burn in air in the presence of oxygen:
3 Mn (s) + 2 Otwo (g) => Mn3OR4 (s)
It can also react with nitrogen at a temperature of approximately 1,200 ° C, to form manganese nitride:
3 Mn (s) + Ntwo (s) => Mn3Ntwo
It also combines directly with boron, carbon, sulfur, silicon, and phosphorus; but not with hydrogen.
Manganese dissolves rapidly in acids, causing salts with the manganese ion (Mntwo+) and releasing hydrogen gas. It reacts equally with halogens, but requires high temperatures:
Mn (s) + Brtwo (g) => MnBrtwo (s)
Manganese can form bonds with carbon atoms, Mn-C, allowing it to originate a series of organic compounds called organomanganese.
In organomanganese the interactions are due either to the Mn-C or Mn-X bonds, where X is a halogen, or to the positioning of the positive center of manganese with the electronic clouds of the conjugated π systems of aromatic compounds.
Examples of the above are the compounds phenylmanganese iodide, PhMnI, and methylcyclopentadienyl manganese tricarbonyl, (C5H4CH3) -Mn- (CO)3.
This last organomanganese forms a Mn-C bond with CO, but at the same time interacts with the aromatic cloud of the C ring5H4CH3, forming a sandwich-like structure in the middle:
Has a single stable isotope 55Mn with 100% abundance. The other isotopes are radioactive: 51Mn, 52Mn, 53Mn, 54Mn, 56Mn and 57Mn.
The structure of manganese at room temperature is complex. Although it is considered body-centered cubic (bcc), experimentally its unit cell has been shown to be a distorted cube.
This first phase or allotrope (in the case of metal as a chemical element), called α-Mn, is stable up to 725 ° C; Once this temperature is reached, a transition occurs to another equally "rare" allotrope, β-Mn. Then, the allotrope β predominates until 1095 ° C when it again becomes a third allotrope: the γ-Mn.
Γ-Mn has two differentiable crystal structures. One face-centered cubic (fcc), and the other face-centered tetragonal (fct) face-centered tetragonal) at room temperature. And finally, at 1134 ° C the γ-Mn is transformed into the allotrope δ-Mn, which does crystallize in an ordinary bcc structure.
Thus, manganese has up to four allotropic forms, all dependent on temperature; and regarding those dependent on pressure, there are not too many bibliographic references to consult them.
In these structures the Mn atoms are linked by a metallic bond governed by their valence electrons, according to their electronic configuration:
[Ar] 3d5 4stwo
The electronic configuration of manganese allows us to observe that it has seven valence electrons; five in the 3d orbital, and two in the 4s orbital. By losing all these electrons during the formation of its compounds, assuming the existence of the cation Mn7+, it is said to acquire an oxidation number of +7 or Mn (VII).
The KMnO4 (K+Mn7+ORtwo-4) is an example of a compound with Mn (VII), and it is easy to recognize by its bright purple colors:
Manganese can gradually lose each of its electrons. Thus, their oxidation numbers can also be +1, +2 (Mntwo+, the most stable of all), +3 (Mn3+), and so on until +7, already mentioned.
The more positive the oxidation numbers, the greater their tendency to gain electrons; that is to say, their oxidizing power will be greater, since they will "steal" electrons from other species to reduce themselves and supply the electronic demand. That is why the KMnO4 it is a great oxidizing agent.
All manganese compounds are characterized by being colorful, and the reason is due to the electronic d-d transitions, different for each oxidation state and their chemical environments. Thus, the compounds of Mn (VII) are usually purple in color, while those of Mn (VI) and Mn (V), for example, are green and blue, respectively..
Mn (II) compounds look a bit washed out, in contrast to KMnO4. For example, the MnSO4 and MnCltwo are pale pinkish, almost white solids.
This difference is due to the stability of the Mntwo+, whose electronic transitions require more energy and, therefore, barely absorb visible light radiation, reflecting almost all of them.
Manganese constitutes 0.1% of the earth's crust and occupies the twelfth place among the elements present in it. Its main deposits are in Australia, South Africa, China, Gabon and Brazil.
Among the main manganese minerals are the following:
-Pyrolusite (MnOtwo) with 63% Mn
-Ramsdelite (MnOtwo) with 62% of Mn
-Manganite (MntwoOR3HtwoO) with 62% Mn
-Cryptomelane (KMn8OR16) with 45 - 60% Mn
-Hausmanite (MnMntwoOR4) with 72% Mn
-Braunite (3MntwoOR3·MnSiO3) with 50 - 60% Mn and the (MnCO3) with 48% of Mn.
Only minerals containing more than 35% manganese are considered commercially exploitable.
Although there is very little manganese in seawater (10 ppm), on the seabed floor there are long areas covered with manganese nodules; also called polymetallic nodules. In these there are accumulations of manganese and some iron, aluminum and silicon.
The manganese reserve of the nodules is estimated to be much greater than the reserve of the metal on the earth's surface..
High-grade nodules contain 10-20% manganese, with some copper, cobalt, and nickel. However, there are doubts about the commercial profitability of mining the nodules..
Manganese is an essential element in the diet of man, since it intervenes in the development of bone tissue; as well as in its formation and in the synthesis of proteoglycans, cartilage formers.
For all this, an adequate manganese diet is necessary, selecting the foods that contain the element.
The following is a list of foods that contain manganese, with the values expressed in mg of manganese / 100 g of the food:
-Pineapple 1.58mg / 100g
-Raspberry and strawberry 0.71 mg / 100g
-Fresh banana 0.27 mg / 100g
-Cooked spinach 0.90 mg / 100g
-Sweet potato 0.45mg / 100g
-Soybean 0.5 mg / 100g
-Cooked kale 0.22mg / 100g
-Cooked broccoli 0.22 mg / 100g
-Chickpea canned 0.54 m / 100g
-Cooked quinoa 0.61 mg / 100g
-Whole wheat flour 4.0 mg / 100g
-Cooked brown rice 0.85 mg / 100g
-Cereals type All Brand 7.33 mg / 100g
-Chia seeds 2.33 mg / 100g
-Toasted almonds 2.14 mg / 100g
With these foods it is easy to meet the manganese requirements, which have been estimated in men at 2.3 mg / day; while women need to ingest 1.8 mg / day of manganese.
Manganese is involved in the metabolism of carbohydrates, proteins and lipids, as well as in bone formation and in the defense mechanism against free radicals.
Manganese is a cofactor for the activity of numerous enzymes, including: superoxide reductase, ligases, hydrolases, kinases, and decarboxylases. Manganese deficiency has been linked to weight loss, nausea, vomiting, dermatitis, growth retardation, and skeletal abnormalities..
Manganese is involved in photosynthesis, specifically in the operation of Photosystem II, related to the dissociation of water to form oxygen. The interaction between Photosystems I and II is necessary for the synthesis of ATP.
Manganese is considered necessary for the fixation of nitrate by plants, a source of nitrogen and a primary nutritional component of plants.
Manganese alone is a metal with insufficient properties for industrial applications. However, when mixed in small proportions with cast iron, the resulting steels. This alloy, called ferromanganese, is also added to other steels, being an essential component to make it stainless.
Not only does it increase its wear resistance and strength, but it also desulfurizes, deoxygenates and dephosphorylates it, removing undesirable S, O and P atoms in steel production. The material formed is so strong that it is used for the creation of railway tracks, prison cage bars, helmets, safes, wheels, etc..
Manganese can also be alloyed with copper, zinc and nickel; i.e. to produce non-ferrous alloys.
Manganese is also used for the production of aluminum alloys, which are normally used for the manufacture of soda or beer cans. These Al-Mn alloys are resistant to corrosion.
Because manganese is beneficial to plants, as MnOtwo or MgSO4 finds use in the formulation of fertilizers, in such a way that the soils are enriched with this metal.
The Mn (VII), expressly as KMnO4, it is a powerful oxidizing agent. Its action is such that it helps to disinfect the waters, with the disappearance of its violet color indicating that it neutralized the microbes present.
It also serves as a titrant in analytical redox reactions; for example, in the determination of ferrous iron, sulphites and hydrogen peroxides. And in addition, it is a reagent to carry out certain organic oxidations, most of the time being synthesis of carboxylic acids; among them, benzoic acid.
Glass naturally has a green color due to its content of ferric oxide or ferrous silicates. If a compound is added that can somehow react with iron and isolate it from the material, then the glass will discolor or lose its characteristic green color..
When manganese is added as MnOtwo with this purpose, and nothing else, the transparent glass ends up taking pink, violet or bluish hues; reason why other metal ions are always added to counteract this effect and keep the glass colorless, if that is the desire.
On the other hand, if there is an excess of MnOtwo, a glass with brown or even black shades is obtained.
Manganese salts, especially MnOtwo, MntwoOR3, MnSO4, MnCtwoOR4 (oxalate), and others, are used to dry flaxseeds or oils at low or high temperatures.
Like other metals, its crystals or aggregates can be as small as nanometric scales; these are manganese nanoparticles (NPs-Mn), reserved for applications other than steels.
NPs-Mn provide greater reactivity when dealing with chemical reactions where metallic manganese can intervene. As long as your synthesis method is green, using plant extracts or microorganisms, the friendlier your potential applications will be with the environment..
Some of its uses are:
-They purify wastewater
-Meet nutritional demands for manganese
-Serve as an antimicrobial and antifungal agent
-Degrade colorants
-They are part of supercapacitors and lithium-ion batteries
-They catalyze the epoxidation of olefins
-Purify DNA extracts
Among these applications, the nanoparticles of their oxides (NPs MnO) can also participate or even replace the metallic ones..
Manganese ions can interact with an organic matrix to establish an organic metal framework (MOF: Metal Organic Framework). Within the porosities or interstices of this type of solid, with directional bonds and well-defined structures, chemical reactions can be produced and catalyzed heterogeneously..
For example, starting from MnCltwo4HtwoO, benzenetricarboxylic acid and N, N-dimethylformamide, these two organic molecules coordinate with Mntwo+ to form a MOF.
This MOF-Mn is capable of catalyzing the oxidation of alkanes and alkenes, such as: cyclohexene, styrene, cyclooctene, adamantane and ethylbenzene, transforming them into epoxides, alcohols or ketones. Oxidations occur within the solid and its intricate crystalline (or amorphous) lattices.
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