Manganese(II) chloride is the di
chloride
The term chloride refers to a compound or molecule that contains either a chlorine anion (), which is a negatively charged chlorine atom, or a non-charged chlorine atom covalently bonded to the rest of the molecule by a single bond (). The pr ...
salt of
manganese
Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...
, MnCl
2. This
inorganic chemical exists in the
anhydrous
A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achie ...
form, as well as the di
hydrate
In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...
(MnCl
2·2H
2O) and tetrahydrate (MnCl
2·4H
2O), with the tetrahydrate being the most common form. Like many Mn(II) species, these salts are pink, with the paleness of the color being characteristic of transition metal complexes with
high spin d
5 configurations.
Preparation
Manganese chloride is produced by treating
manganese(IV) oxide with concentrated hydrochloric acid.
:MnO
2 + 4 HCl → MnCl
2 + 2 H
2O + Cl
2
In the 19th century this reaction
was used for the manufacture of
chlorine
Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...
. By carefully neutralizing the resulting solution with MnCO
3, one can selectively precipitate iron salts, which are common impurities in manganese dioxide.
[.]
In the laboratory, manganese chloride can be prepared by treating
manganese
Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...
metal or
manganese(II) carbonate with
hydrochloric acid
Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...
:
:Mn + 2 HCl + 4 H
2O → MnCl
2(H
2O)
4 + H
2
:MnCO
3 + 2 HCl + 3 H
2O → MnCl
2(H
2O)
4 + CO
2
Structures
Anhydrous MnCl
2 adopts a layered
cadmium chloride-like structure. The tetrahydrate consists of octahedral ''
cis''-Mn(H
2O)
4Cl
2 molecules. The trans isomer, which is metastable, is also known. The dihydrate MnCl
2(H
2O)
2 is a
coordination polymer. Each Mn center is coordinated to four doubly
bridging chloride ligands. The octahedron is completed by a pair of mutually trans
aquo ligands.
Chemical properties
The hydrates dissolve in water to give mildly acidic solutions with a
pH of around 4. These solutions consist of the
metal aquo complex
In chemistry, metal aquo complexes are coordination compounds containing metal ions with only water as a ligand. These complexes are the predominant species in aqueous solutions of many metal salts, such as metal nitrates, sulfates, and perchlo ...
n(H2O)6sup>2+.
It is a weak
Lewis acid
A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any ...
, reacting with
chloride
The term chloride refers to a compound or molecule that contains either a chlorine anion (), which is a negatively charged chlorine atom, or a non-charged chlorine atom covalently bonded to the rest of the molecule by a single bond (). The pr ...
ions to produce a series of salts containing the following ions
nCl3sup>
−,
nCl4sup>2
−, and
nCl6sup>4
−.
Upon treatment with typical organic ligands, manganese(II) undergoes oxidation by air to give Mn(III)
complexes. Examples include
n(EDTA)">EDTA.html" ;"title="n(EDTA">n(EDTA)sup>
−, [Mn(cyanide">CN)
6">EDTA">n(EDTA)">EDTA.html" ;"title="n(EDTA">n(EDTA)sup>
−, [Mn(cyanide">CN)
6sup>3
−, and [Mn(acetylacetonate)
3]. Triphenylphosphine forms a labile 2:1 adduct:
:MnCl
2 + 2 triphenylphosphine, Ph
3P → [MnCl
2(Ph
3P)
2]
Anhydrous manganese(II) chloride serves as a starting point for the synthesis of a variety of
organomanganese compounds. For example,
manganocene is prepared by reaction of MnCl
2 with a solution of
sodium cyclopentadienide
Sodium cyclopentadienide is an organosodium compound with the formula C5H5Na. The compound is often abbreviated as NaCp, where Cp− is the cyclopentadienide anion. Sodium cyclopentadienide is a colorless solid, although samples often are pin ...
in
tetrahydrofuran
Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water- miscible organic liquid with low viscosity. It is ...
(THF).
:MnCl
2 + 2 NaC
5H
5 → Mn(C
5H
5)
2 + 2 NaCl
Similar reactions are used in the preparation of the antiknock compound
methylcyclopentadienyl manganese tricarbonyl.
[
Manganese chloride is a precursor to organomanganese reagents in organic chemistry.
Manganese chloride is mainly used in the production of dry cell batteries.
]
Magnetism
Manganese(II) salts are paramagnetic. As such the presence of such salts profoundly affect NMR spectra.
Natural occurrence
Scacchite is the natural, anhydrous form of manganese(II) chloride.
Precautions
Manganism, or manganese poisoning, can be caused by long-term exposure to manganese dust or fumes.
References
External links
National Pollutant Inventory: Manganese and compounds Fact Sheet
{{Chlorides
Chlorides
Manganese(II) compounds
Metal halides